a327ex.com

Mini Looper 1

Summary

First session on the rebooted Mini Looper — a SNKRX-style train that auto-follows a looping road around a defended center. The entire session was about getting the train's movement right (the novel core mechanic). Enemies and attacks are deferred to next session. Ended on a clean pure-SNKRX trail-follow snake whose turn response auto-scales with speed.

Project setup / repo rename:

Design discussion (concept + fun-gates):

Path representation — rejected the old arc-spline/piece-editor:

Step 1 — single steered unit + push test (train.lua):

Movement smoothing — key iterations:

Conga (followers):

Box2D distance-joint engine integration:

Physics chain (2b) + hybrid (2c):

THE trail-build bug (root cause of "followers don't follow"):

Final decision — pure SNKRX, physics removed:

Final spacing bug:

Locked-in defaults: 12 units; SPEED 100, SEEK 15, SPACING 12; EASE P 0.70 fixed; EASE T/CORNER auto-derived from speed. Movement considered DONE. Next session: enemies + attacks.

Let's work on Mini Looper. There's one folder with the old version of it, mini-looper. We want to rename this to mini-looper-old, both locally and on GitHub, because we'll create the project anew (in a new mini-looper folder) using the new SNKRX template (snkrx-template/). So do all that first, please.

I'll start by exploring the current state — the existing mini-looper folder, its git remote, and the snkrx-template/ structure.

Bash (ls -la | head -50)

total 532
drwxr-xr-x 1 adn 197121      0 May 30 22:31 ./
drwxr-xr-x 1 adn 197121      0 May 25 09:48 ../
drwxr-xr-x 1 adn 197121      0 May 31 16:46 .claude/
drwxr-xr-x 1 adn 197121      0 Apr 21 08:37 .kimi/
drwxr-xr-x 1 adn 197121      0 Feb 12 17:38 Anchor/
drwxr-xr-x 1 adn 197121      0 Feb 24 08:19 Anchor-YueScript/
drwxr-xr-x 1 adn 197121      0 Feb 23 08:17 Anchor-lua/
drwxr-xr-x 1 adn 197121      0 May 27 21:39 Anchor2/
drwxr-xr-x 1 adn 197121      0 May  1 17:23 BYTEPATH/
drwxr-xr-x 1 adn 197121      0 Apr  2 07:23 Danpenzero/
drwxr-xr-x 1 adn 197121      0 May 27 23:27 Invoker/
drwxr-xr-x 1 adn 197121      0 May 15 23:20 Invoker-old/
drwxr-xr-x 1 adn 197121      0 May 31 11:46 Null/
drwxr-xr-x 1 adn 197121      0 Apr 18 18:57 Psyonia/
drwxr-xr-x 1 adn 197121      0 Apr 22 14:34 RETICLE/
drwxr-xr-x 1 adn 197121      0 Mar  7 04:01 RTFX/
drwxr-xr-x 1 adn 197121      0 May 28 00:07 Ricochet/
drwxr-xr-x 1 adn 197121      0 Feb 15 13:32 SNKRX/
drwxr-xr-x 1 adn 197121      0 May 31 11:43 a327ex-site/
drwxr-xr-x 1 adn 197121      0 Apr 11 17:25 a327ex.com-blog/
drwxr-xr-x 1 adn 197121      0 May  3 14:40 anchor.blot.im/
-rw-r--r-- 1 adn 197121  25703 Feb 19 15:32 cute_action.mp3
-rw-r--r-- 1 adn 197121 177550 Feb 19 15:33 cute_action.wav
drwxr-xr-x 1 adn 197121      0 May 14 13:46 data/
drwxr-xr-x 1 adn 197121      0 May 16 23:37 edition-template/
drwxr-xr-x 1 adn 197121      0 May 16 12:39 emoji-aimer/
drwxr-xr-x 1 adn 197121      0 Feb 26 17:23 emoji-ball-battles/
drwxr-xr-x 1 adn 197121      0 Feb 22 11:22 emoji-ball-battles-generated/
drwxr-xr-x 1 adn 197121      0 Apr 27 20:54 emoji-ball-bounce/
... [20 more lines]

Bash (cd /e/a327ex/mini-looper 2>/dev/null && echo "=== mini-looper exists ===" && ls ...)

=== mini-looper exists ===
total 4201
drwxr-xr-x 1 adn 197121       0 May 27 23:33 ./
drwxr-xr-x 1 adn 197121       0 May 30 22:31 ../
drwxr-xr-x 1 adn 197121       0 May 27 20:48 .claude/
drwxr-xr-x 1 adn 197121       0 May 27 23:50 .git/
drwxr-xr-x 1 adn 197121       0 May 26 09:07 anchor/
-rwxr-xr-x 1 adn 197121 4185088 May 24 11:46 anchor.exe*
drwxr-xr-x 1 adn 197121       0 May 26 09:07 assets/
-rw-r--r-- 1 adn 197121    3650 May 27 21:06 grid.lua
-rw-r--r-- 1 adn 197121   22564 May 27 23:33 main.lua
-rw-r--r-- 1 adn 197121     730 May 27 23:36 map.lua
-rw-r--r-- 1 adn 197121   10028 May 27 12:06 path.lua
-rw-r--r-- 1 adn 197121   12259 May 27 23:32 path_editor.lua
-rw-r--r-- 1 adn 197121    6649 May 27 21:37 pieces.lua
-rw-r--r-- 1 adn 197121    4023 May 27 21:45 pieces_gallery.lua
-rw-r--r-- 1 adn 197121    3651 May 27 22:02 pieces_search.lua
-rw-r--r-- 1 adn 197121     189 May 26 09:07 run.bat
-rw-r--r-- 1 adn 197121    4812 May 27 23:32 snake.lua
drwxr-xr-x 1 adn 197121       0 May 27 20:48 snkrx/
=== git remote ===
origin  git@github.com:a327ex/mini-looper.git (fetch)
origin  git@github.com:a327ex/mini-looper.git (push)
=== git status ===
On branch main
Your branch is up to date with 'origin/main'.

nothing to commit, working tree clean

The situation is clear. Let me gather a bit more before acting: check gh auth status, the snkrx-template/ structure, and whether the template carries its own git history.

Bash (cd /e/a327ex && echo "=== gh auth ===" && gh auth status 2>&1 | head -10 && echo...)

=== gh auth ===
github.com
  ✓ Logged in to github.com account a327ex (keyring)
  - Active account: true
  - Git operations protocol: ssh
  - Token: gho_************************************
  - Token scopes: 'admin:public_key', 'gist', 'read:org', 'repo'

=== mini-looper-old exists already? ===
no (good)

Bash (cd /e/a327ex && echo "=== snkrx-template top-level ===" && ls -la snkrx-template...)

=== snkrx-template top-level ===
total 4201
drwxr-xr-x 1 adn 197121       0 May 31 17:15 ./
drwxr-xr-x 1 adn 197121       0 May 30 22:31 ../
drwxr-xr-x 1 adn 197121       0 May 31 17:15 .claude/
drwxr-xr-x 1 adn 197121       0 May 31 17:21 .git/
-rw-r--r-- 1 adn 197121    5214 May 31 17:15 README.md
drwxr-xr-x 1 adn 197121       0 May 17 22:24 anchor/
-rwxr-xr-x 1 adn 197121 4185088 May 31 12:02 anchor.exe*
drwxr-xr-x 1 adn 197121       0 May 31 12:19 assets/
-rw-r--r-- 1 adn 197121   16730 May 31 16:56 main.lua
-rw-r--r-- 1 adn 197121   28688 May 25 02:05 main_old.lua
-rw-r--r-- 1 adn 197121   18873 May 31 16:56 main_scaffold.lua
-rw-r--r-- 1 adn 197121     365 May 31 16:46 run.bat
drwxr-xr-x 1 adn 197121       0 May 31 15:25 snkrx/

=== snkrx-template has its own .git? ===
snkrx-template/.git/
origin  git@github.com:a327ex/snkrx-template.git (fetch)
origin  git@github.com:a327ex/snkrx-template.git (push)

Everything checks out: gh is authed as a327ex with repo scope, no local mini-looper-old exists, and the template carries its own .git (pointing at a327ex/snkrx-template) which I must NOT carry into the fork.

Let me verify there's no naming collision on GitHub before renaming.

Bash (echo "=== does a327ex/mini-looper exist? ===" && gh repo view a327ex/mini-looper...)

=== does a327ex/mini-looper exist? ===
{"name":"mini-looper","sshUrl":"git@github.com:a327ex/mini-looper.git","visibility":"PRIVATE"}

=== does a327ex/mini-looper-old already exist (collision check)? ===
GraphQL: Could not resolve to a Repository with the name 'a327ex/mini-looper-old'. (repository)

No collision, repo is private. Now I'll execute the renames. First the GitHub rename, then the local folder rename + remote URL update.

Bash (echo "=== renaming GitHub repo ===" && gh repo rename mini-looper-old --repo a32...)

=== renaming GitHub repo ===

=== verify ===
{"name":"mini-looper-old","sshUrl":"git@github.com:a327ex/mini-looper-old.git","visibility":"PRIVATE"}

GitHub repo renamed to mini-looper-old. Now the local folder rename and remote URL update.

Bash (echo "=== renaming local folder ===" && mv mini-looper mini-looper-old && echo "...)

=== renaming local folder ===
done

=== updating local remote URL ===
origin  git@github.com:a327ex/mini-looper-old.git (fetch)
origin  git@github.com:a327ex/mini-looper-old.git (push)

=== verify connectivity to renamed remote ===

Let me confirm the renamed remote is reachable (the ls-remote output came back empty, which is worth verifying).

Bash (git ls-remote origin 2>&1 | head -5; echo "exit: $?")

40f8bb3305ef96a779de5f014edee115b9ffdad9 HEAD
40f8bb3305ef96a779de5f014edee115b9ffdad9    refs/heads/main
exit: 0

Remote is reachable — refs/heads/main resolves. Renames are fully done:

Now I'll create the new mini-looper/ by forking the template — copying everything except the template's .git (so it doesn't inherit the snkrx-template history/remote).

Bash (cd /e/a327ex && mkdir mini-looper && cp -r snkrx-template/* mini-looper/ && cp -...)

=== new mini-looper contents ===
total 4197
drwxr-xr-x 1 adn 197121       0 May 31 23:00 ./
drwxr-xr-x 1 adn 197121       0 May 31 23:00 ../
drwxr-xr-x 1 adn 197121       0 May 31 23:00 .claude/
-rw-r--r-- 1 adn 197121    5214 May 31 23:00 README.md
drwxr-xr-x 1 adn 197121       0 May 31 23:00 anchor/
-rwxr-xr-x 1 adn 197121 4185088 May 31 23:00 anchor.exe*
drwxr-xr-x 1 adn 197121       0 May 31 23:00 assets/
-rw-r--r-- 1 adn 197121   16730 May 31 23:00 main.lua
-rw-r--r-- 1 adn 197121   28688 May 31 23:00 main_old.lua
-rw-r--r-- 1 adn 197121   18873 May 31 23:00 main_scaffold.lua
-rw-r--r-- 1 adn 197121     365 May 31 23:00 run.bat
drwxr-xr-x 1 adn 197121       0 May 31 23:00 snkrx/

=== confirm NO .git carried over ===
good — no .git

The new mini-looper/ is a clean fork of the template with no .git carried over.

Two setup decisions remain before this is ready — both have valid alternatives, so I'd rather confirm than guess:

AskUserQuestion 

Your questions have been answered: "How should I set up git for the new mini-looper/ folder? (Renaming on GitHub freed up the 'mini-looper' name.)"="Fresh repo + new GitHub repo", "The fork carried over the template's build artifacts (main_old.lua, main_scaffold.lua). Keep them or prune for a clean start?"="Keep everything". You can now continue with these answers in mind.

Both decisions noted: fresh repo + new private GitHub repo, and keep all template files. Initializing git and making the initial commit now.

Bash (cd /e/a327ex/mini-looper && git init -b main 2>&1 && git add -A && git commit -m...)

Initialized empty Git repository in E:/a327ex/mini-looper/.git/
warning: in the working copy of '.claude/CLAUDE.md', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'README.md', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/animation.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/camera.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/class.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/collider.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/color.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/font.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/image.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/init.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/input.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/memory.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/object.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/physics.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/shake.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/spring.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/spritesheet.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'anchor/timer.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'assets/draw_shader.frag', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'main.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'main_old.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'main_scaffold.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'run.bat', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/airborne.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/area.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/beam.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/effect.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/effect_lab.lua', LF will be replaced by CRLF the next time Git touches it
warning: in the working copy of 'snkrx/findings.md', LF will be replaced by CRLF the next time Git touches it
... [27 more lines]

Initial commit landed (the LF→CRLF warnings are just line-ending normalization, harmless). Now creating the new private GitHub repo and pushing.

Bash (git log --oneline -1 && echo "" && echo "=== creating + pushing new GitHub repo ...)

b837ebc Initial commit: fork from snkrx-template

=== creating + pushing new GitHub repo ===
https://github.com/a327ex/mini-looper
branch 'main' set up to track 'origin/main'.
To github.com:a327ex/mini-looper.git
 * [new branch]      HEAD -> main

=== verify remote ===
origin  git@github.com:a327ex/mini-looper.git (fetch)
origin  git@github.com:a327ex/mini-looper.git (push)

All done. Let me do a final verification of the GitHub state for both repos.

Bash (echo "=== a327ex/mini-looper-old (old version) ===" && gh repo view a327ex/mini-...)

=== a327ex/mini-looper-old (old version) ===
{"name":"mini-looper-old","pushedAt":"2026-05-28T02:51:10Z","sshUrl":"git@github.com:a327ex/mini-looper-old.git","visibility":"PRIVATE"}

=== a327ex/mini-looper (new, from template) ===
{"name":"mini-looper","pushedAt":"2026-06-01T02:02:44Z","sshUrl":"git@github.com:a327ex/mini-looper.git","visibility":"PRIVATE"}

All set. Here's the final state:

Old version → renamed to mini-looper-old

New project → fresh mini-looper/ from the SNKRX template

Note: the GitHub auto-redirect from the old name is now consumed — a327ex/mini-looper points at the brand-new repo, and the old one lives only at a327ex/mini-looper-old. Any stale clone still pointing at the old URL would now hit the new repo, but your local mini-looper-old/ is correctly repointed.

One thing worth flagging for when we start designing: the fork carried over the template's README.md and .claude/CLAUDE.md, which still describe the template itself rather than Mini Looper. No rush, but we'll likely want to rewrite those once the new direction takes shape — I left them untouched per your "keep everything" choice.

The folder's ready. What's the direction for the new Mini Looper — want to talk through the design before any code?

Yes, let's talk design. As per our new operating directives, I want to try to quickly assess if the game is fun or not. The main game entity is a SNKRX snake composed of multiple units, except they're not controlled by the player, they follow a looping path/road that protects a center, and in this center are buildings the player can place to improve his build. Each unit in the train attacks automatically, like in SNKRX, and enemies appear from the side of the screen towards the center. A fairly simple game loop where you want to get more powerful and choose the right units + build combos so your build can deal with the increasing waves of enemies.

I think the primary test is getting this entire thing working on a moment-to-moment basis, so looping train, units in it auto-attacking, building placement, enemy spawning and being dealt damage by hits, enemies hitting buildings, enemies hitting the central building and winning. Then, we want to assess if the endgame feels fun, so we need to test a few fixed but varied endgame builds that represent a few archetypes of play. If those feel fun, then the process of getting to them will be worthy and we can proceed to producing the game in more detail.

Before I lay out the design conversation, let me ground myself in two things: what the old Mini Looper already solved (it had path.lua / snake.lua / path_editor.lua), and what the new template gives us for free.

Read (E:\a327ex\mini-looper-old\path.lua)

1    --[[
2     path.lua — line + arc paths with arc-length lookup and ribbon draw.
3   
4     A path is a closed or open curve made of straight-line and circular-arc
5     segments. It is built in two phases:
6   
7       1. AUTHORING (build a command list)
8            p = path_new({ width = 20 })
9            path_move_to(p, x, y)               -- set start cursor
10           path_line_to(p, x, y)               -- straight to (x, y)
11           path_arc(p, cx, cy, sweep)          -- arc from cursor, centered
12                                               -- at (cx, cy), sweeping by
13                                               -- `sweep` radians (positive
14                                               -- = visually CW in screen
15                                               -- y-down coords). Radius is
16                                               -- inferred from |cursor -
17                                               -- center|.
18           path_close(p)                       -- mark closed. If the path
19                                               -- doesn't actually close
20                                               -- (cursor != start with
21                                               -- matching heading), emits
22                                               -- a straight line + prints
23                                               -- a warning so the kink is
24                                               -- visible. No auto-bridge.
25  
26      2. BAKE (lazy — runs on first query / draw)
27           path_finalize(p)
28         Walks the commands and emits a sampled polyline + a parallel
29         cumulative arc-length table. Lines emit 2 samples (start + end —
30         lerp between them is exact). Arcs emit max(2, ceil(arc_length *
... [248 more lines]

Read (E:\a327ex\mini-looper-old\snake.lua)

1    --[[
2     snake.lua — the on-rails SNKRX-style chain.
3   
4     A `snake` is a chain of N identical `snake_unit` entities sampled at
5     fixed arc-length offsets along a `path`. The head advances over time;
6     every body unit's position is just `path_at(path, head_s - i*spacing)`.
7     No steering, no follow-the-leader physics, no easing — the sample IS
8     the position. The path's arc-length parametrization does all the work.
9   
10    PHYSICS
11      Each unit has a KINEMATIC box collider. Kinematic means: Box2D won't
12      move it in response to forces, but it produces contact / sensor
13      events normally and behaves like a moving wall to other dynamics.
14      That's the right model for a path-pinned entity — we own its
15      position, but seekers / projectiles should still hit it. We move it
16      via `set_position` + `set_angle` each frame; we never read those
17      back. At the snake's nominal speed (~120 units/sec ≈ 2px / frame)
18      teleporting is fine; if we ever need accurate contact velocity
19      imparted to dynamics (e.g. snake-as-paddle), switch to velocity-
20      driven motion at that point.
21  
22      Tag is `'snake'`. snake↔enemy / snake↔wall collisions are enabled in
23      main.lua; snake↔snake is deliberately NOT enabled — adjacent units
24      can overlap on tight curves without constraint-solver churn.
25  
26    USAGE
27      snake_build(demo_path)                  -- spawns the chain
28      snake_update(snake, sdt)                -- in update(), after p:update
29      snake_draw(snake, game_layer)           -- in draw(), inside game_layer
30                                              -- camera attach
... [105 more lines]

Bash (echo "=== new template snkrx/ ===" && ls snkrx-template/snkrx/ && echo "" && ech...)

=== new template snkrx/ ===
airborne.lua
area.lua
beam.lua
effect.lua
effect_lab.lua
findings.md
flicker.lua
fx.lua
geometry.lua
init.lua
palette.lua
player.lua
projectile.lua
prop.lua
seeker.lua
sound_tuner.lua
sound_tuning.lua
stats.lua
ui/
wall.lua

=== old mini-looper file sizes (reuse candidates) ===
-rw-r--r-- 1 adn 197121  3650 May 27 21:06 mini-looper-old/grid.lua
-rw-r--r-- 1 adn 197121 22564 May 27 23:33 mini-looper-old/main.lua
-rw-r--r-- 1 adn 197121   730 May 27 23:36 mini-looper-old/map.lua
-rw-r--r-- 1 adn 197121 10028 May 27 12:06 mini-looper-old/path.lua
-rw-r--r-- 1 adn 197121 12259 May 27 23:32 mini-looper-old/path_editor.lua
-rw-r--r-- 1 adn 197121  6649 May 27 21:37 mini-looper-old/pieces.lua
-rw-r--r-- 1 adn 197121  4023 May 27 21:45 mini-looper-old/pieces_gallery.lua
... [2 more lines]

I read the old path.lua / snake.lua and the template toolkit. Good news up front, then the design substance.

The mechanical heart — and it's mostly already built

The thing that makes this not just SNKRX-on-autopilot is the rotating coverage gap. A single train sweeping a closed loop is a mobile 360° perimeter, but the train only occupies a contiguous arc of the loop (length = count × spacing). If the loop's perimeter is longer than the train, there is always a cold arc — and enemies that pour in through the cold arc reach the center unobstructed, while enemies hitting the hot arc get blocked and shot. So the train's current position on the loop decides which incoming directions are defended right now. That tension — "the wave's coming from the south but my train is on the north side" — is the whole game, or there is no game.

And this falls out of the existing code almost for free. The old snake.lua already pins a chain of kinematic box colliders to a path via arc-length sampling — kinematic means they act as moving walls to enemies but we own their position. So the train is literally a moving wall ring with a gap, with zero new physics. path.lua already gives closed loops with path_at(s) lookup. The template gives us:

So the first-gate machine is assembly, not invention: port path.lua + snake.lua, give units an auto-attack timer, seek enemies to center, add a center "core" entity with HP, spawn waves from the edges. A few days of work, not weeks.

Two gates, one machine

Your two-part test maps exactly onto the build-heavy pipeline directive, and I want to flag the efficient version: gate 1 and gate 2 are the same machine with different constants.

Same code, swap the numbers (and ideally a 1/2/3 hotkey to hot-load each endgame build so you can compare archetypes in one sitting). This is the directive's "hardcode a fake powered build — do NOT build the ability/modifier/orb systems to get there." I'll hold that line hard: no progression, shop, or upgrade systems to reach the endgame builds. We literally if key 2 then spawn_build_swarm().

Two honest risks

1. The spectator problem. Your spec says the snake is "not controlled." Taken literally, that means during a wave the player does nothing — all agency is between-wave placement. That's a coherent game (it's an autobattler/TD-watch), but it makes the gate-1 question — "does second-to-second feel good?" — hard to judge in grey-box, because the second-to-second fun would ride almost entirely on spectacle + breach drama, which is exactly what rough rectangles show worst.

The cheap remedy is a 1-D verb: throttle the train — the player controls its speed (and maybe reverse) along the fixed loop, to rush the hot arc to wherever the breach is. That's not SNKRX steering (you can't leave the road) — it keeps the "on rails" identity but gives a real, grey-box-visible decision every second. The nice part: this isn't a fork we're locked into. The machine supports both — we can toggle throttle on/off and feel the difference in the same sitting. So I lean throttle, but if your intended fun is genuinely the build-craft autobattler (watch the build resolve, TFT-style), pure-auto is the honest choice and we just judge gate-1 by the between-wave decisions + breach drama instead.

2. Power fantasy is partly a juice phenomenon. Gate 2 asks "is the screen-clearing endgame fun?" — but a lot of "power fantasy" is big numbers, screenshake, particles, sound. Pure grey-box would undersell it and we'd risk a false "not fun." Mitigant: the template carriers already ship their FX (hit circles, particles, shake, sounds, hit-stop, edition shimmer), so this isn't truly juiceless — it's fairer than rectangles-only. We judge gate 2 on structure (do archetypes clear waves in mechanically distinct, interesting ways) and accept we can't fully judge the visceral layer until production.

Endgame archetypes for gate 2

Three that are mechanically distinct and map cleanly to the carriers + different relationships to the loop (so we're testing the space, not one point):

All four are hardcodeable by setting unit count + carrier params + building set. No systems.

Defaults I'll assume unless you say otherwise: lose when the core's HP hits 0 (your "enemies… winning" = run ends); no formal victory in the prototype — survival against escalating waves, "win" = reach a target wave. Enemies path straight to the core and get blocked/shot only by the arc the train currently occupies.

Three decisions drive the prototype's scope:

AskUserQuestion 

Your questions have been answered: "During a wave, what does the player actually DO? SNKRX's skill is steering; your snake is on rails — so where does the live, second-to-second agency come from?"="Agency happens in waves and between them, kind of like how tower defense games work where you can place new towers at any point in time based on your resources, although not exactly like that either.", "What buildings exist in the FIRST prototype (the core-loop gate)?"="Not sure yet.", "Fixed loop or player-drawn loop for the prototype?"="I want to talk more about this actually, I want you to not use the previous Mini Looper's solution for the path and try something new.". You can now continue with these answers in mind.

Your three answers reshape the design in a good way. Let me synthesize, because I think your placement answer quietly solved a problem — and then let's actually talk about the path, which is what you asked for.

What your answer does to the design

Your "place things based on resources, but not exactly TD" answer resolves the spectator worry better than my throttle idea did, and it locks into the loop tension instead of sitting beside it. Worth saying out loud:

The cold arc is the problem; live placement is the answer. A fixed-speed auto train can only defend the arc it's currently on — there's always an undefended side, and you can't move the coverage to a breach. But you can drop a building to plug the side the train isn't on. So the live verb becomes: "train's up north, enemies are pouring in from the south — spend resources, reinforce the south." That's TD placement, it's visible in grey-box, and — the part I like — it's created by the loop's geometry rather than bolted on. The loop manufactures the problem; placement is the counterplay. They're the same mechanic seen from two ends.

And it's "not exactly TD" for a concrete reason: in classic TD the towers are your damage. Here the moving train is the star, and buildings exist to cover for the train's absence and/or buff it as it sweeps past. That's the distinction worth protecting. (Resources = kills feeding a currency you spend anytime; we stub that for the gate, it's an economy not a system to design now. And throttle stays in my back pocket as a cheap toggle if placement-only tests too passive.)

The path — let's talk

First, the elephant, because naming it sharpens everything: this is Loop Hero's skeleton (an auto-walker on a loop; you place things around it to build power) wired onto SNKRX's body (a many-unit auto-attacking train) over a TD heart (defend a besieged center). I think that mashup is Mini Looper. Borrow from Loop Hero: the loop-as-placement-substrate, the auto-walker. Diverge from it: your looper is a defensive perimeter of many units, not one hero, and the middle is a base under siege.

Before the menu — what actually bugged you about the old arc-spline + piece-editor path? Too fiddly to author? Didn't generate variety? The editor ate the session? Closing the loop was finicky (its own docs warn about non-closing kinks)? Your answer aims this more than any option I can list.

The design space has three axes:

Concrete candidates:

A. Cell-chain loop (my lean for the gate). The loop is an ordered ring of grid cells; cells on/beside the loop are the placement slots. Key point so "grid" ≠ "blocky": the train still glides smoothly — a cell-chain is just a polyline through cell centers, sampled exactly like the old path_at, optionally with rounded corners. The grid buys you legible placement and trivial generation later; it costs nothing in motion smoothness. Lowest infra of all options (less than the old editor), best fit for your placement agency, makes "Mini Looper" literal. Risk: reads as derivative of Loop Hero.

B. Generated smooth blob loop. An organic closed curve from a few parameters (radius-as-noise around the center, or a randomized superellipse) — no pieces, no editor. Train glides; buildings placed at free interior positions. Prettier and more organic, but continuous placement is fiddlier and less slot-legible, and it's the closest cousin to the old continuous approach.

C. Player-grown loop. The loop starts tiny and you spend resources to append road segments, so it grows over the run. Loop length becomes a core tradeoff — more length = more slots and coverage area, but the train patrols a bigger perimeter, so the cold arc grows too. The deepest idea (the loop itself becomes a build choice), but the heaviest to build and the most likely to balloon a gate.

(Wilder, probably post-gate: D a polar/sector loop where "coverage" is literally an angular sector — makes the rotating-coverage math explicit; E a rail network with junction switches the player flips — adds routing as a live verb; F concentric lanes with a train per ring.)

For the fun-gate we build exactly one fixed loop, whatever the representation — no generation, no editor, no grow mechanic. Generation and growing are production deepenings we validate-then-build, not gate work.

Two things to react to — and feel free to riff in "Other," since you wanted to talk this through rather than just vote:

AskUserQuestion 

Your questions have been answered: "Which path direction pulls you for Mini Looper? (We'd still build just ONE fixed loop for the gate — this is about representation, not generation.)"="Something else", "What ARE the buildings — towers, train-buffs, or both? (You said 'not sure yet'; here's the spectrum to react to.)"="[No preference]". You can now continue with these answers in mind.

[Request interrupted by user]

Your model of the game is a bit off. The train is never slow enough that it stays outside a portion of the screen for too long, so most of the issues you have with undefended sides are not real. As for the path, I just want something simpler to start with, let's just go with points in a sequence, and then the train uses the path following steering behavior to go through the points. So there's no defined path necessarily, but in practice that's how it works. This also allows the train to be slightly moved around by enemies and makes it feel more organic and physical, which is always a good thing.

You're right, and I'll drop the cold-arc theory — it was overbuilt. If the train sweeps the whole loop fast, there's no persistent undefended side, so "placement plugs the gap" isn't the spine. Let me recalibrate honestly, but first let me ground the steering approach you described in the actual toolkit.

Grep (steering_follow_path|steering_seek|steering_arrive|steering_separate|function collider:steering)

161:    local sx, sy = self.collider:steering_seek(target_x, target_y, max_speed, max_force)
170:function collider:steering_seek(x, y, max_speed, max_force)
180:function collider:steering_flee(x, y, max_speed, max_force)
190:function collider:steering_arrive(x, y, rs, max_speed, max_force)
205:function collider:steering_pursuit(target, max_speed, max_force)
211:  return self:steering_seek(target.x + tvx*look_ahead, target.y + tvy*look_ahead, max_speed, max_force)
214:function collider:steering_evade(pursuer, max_speed, max_force)
223:function collider:steering_wander(d, rs, jitter, dt, max_speed, max_force)
231:  return self:steering_seek(tx, ty, max_speed, max_force)
234:function collider:steering_separate(rs, others, max_speed, max_force, spatial_hash)
287:function collider:steering_align(rs, others, max_speed, max_force)
308:function collider:steering_cohesion(rs, others, max_speed, max_force)
318:    return self:steering_seek(dx, dy, max_speed, max_force)
324:  steering_follow_path(path, index, seek_distance, max_speed, max_force)
335:function collider:steering_follow_path(path, index, seek_distance, max_speed, max_force)
345:  local fx, fy = self:steering_seek(p.x, p.y, max_speed, max_force)
364:function collider:steering_flow_field(flow_field, max_speed, max_force)
412:function collider:steering_wall_avoidance(max_speed, max_force, opts)

Read (E:\a327ex\mini-looper\anchor\collider.lua)

140  end
141 function collider:add_polygon(tag, vertices, opts)
142   return physics_add_polygon(self.body, tag, vertices, opts or {})
143 end
144 function collider:add_chain(tag, vertices, is_loop)
145   return physics_add_chain(self.body, tag, vertices, is_loop)
146 end
147 
148 -- Body queries
149 function collider:get_mass() return physics_get_mass(self.body) end
150 function collider:set_center_of_mass(x, y) physics_set_center_of_mass(self.body, x, y) end
151 function collider:get_body_type() return physics_get_body_type(self.body) end
152 function collider:is_awake() return physics_is_awake(self.body) end
153 function collider:set_awake(awake) physics_set_awake(self.body, awake) end
154 function collider:get_shapes_geometry() return physics_get_shapes_geometry(self.body) end
155 
156 --[[
157   Steering behaviors.
158   Each returns (fx, fy) force vectors that can be combined and applied.
159 
160   Usage:
161     local sx, sy = self.collider:steering_seek(target_x, target_y, max_speed, max_force)
162     local wx, wy = self.collider:steering_wander(50, 50, 20, dt, max_speed, max_force)
163     self.collider:apply_force(sx + wx, sy + wy)
164 
165   Behaviors use self.owner.x, self.owner.y as the position reference. The owner
166   must have its .x/.y fields up-to-date (either synced from physics via :sync()
167   or set directly).
168 ]]
169 
... [200 more lines]

That clears up my model — thank you for the correction. Let me recalibrate, then I checked the actual steering function so the approach is grounded, and I'll put the first slice as a design brief.

Recalibration

Cold-arc is dead. If the train sweeps the whole loop fast, coverage is effectively global, so the challenge is a throughput race — incoming enemy HP/sec vs your train's DPS, inside the spatial window between the edge and the core — and the levers are unit composition and (later) building placement, not "which side is covered." The loop earns its keep as the SNKRX identity, a way the train spreads its DPS across clusters as it sweeps, the organic physical feel you want, and a placement substrate down the line. I won't re-theorize past that; we'll feel the real texture by playing it.

What I confirmed about the steering

⛔ DESIGN BRIEF — Slice 1: the steered train + core + enemies (no buildings)

What this slice tests. The novel thing — a steered, jostleable train sweeping a waypoint loop — plus just enough combat to read it. It answers: does the train's motion + auto-attack read and feel good, and can I tune wave pressure to a knife-edge? Buildings / agency are deliberately out — that's Slice 2, once we've felt this. (If the train motion alone already feels wrong, we kill it cheap before adding combat — happy to split this into "train moves" then "combat" if you want that checkpoint.)

New files, each beside main.lua, required after require('snkrx'):

loop.lua — loop_points, a list of {x, y} around the center, built by build_loop_ring(cx, cy, rx, ry, n) (n points on an ellipse). Debug-draws the points + connecting segments. Built once at scene start; it's just a point list the train walks — nothing baked.

train.lua — train = { units = {...}, head_index = 1 }. Each train_unit is a class() with make_entity, a dynamic box collider (tag 'train'), a .spec, and an auto-attack timer + range.

core.lua — core, a class() entity at center: static box collider (tag 'core'), hp / hp_max, .spec, a hit-flash spring. core:hit(dmg) drops hp + flashes + spawns particles; hp <= 0 sets a game_over flag (freeze + text for now — no restart UI yet). Draws a chunky rounded-rect with an HP readout (ui_hud_bar) above it. The lose condition lives here.

waves.lua — waves_update(dt): a timer spawns seekers at random points on the screen edges, each retargeted at the core; spawn rate + count ramp over time so I can dial the pressure. Tracks a wave counter for readout.

Seeker retarget (minimal edit to snkrx/seeker.lua or via a spawn arg): give the seeker a target = the core instead of the player p, so its existing steering_seek aims inward. On contact with the core it calls core:hit and dies (kamikaze — simplest; alt is lingering contact damage).

main.lua wiring (interfaces).

Minor defaults (override in your reply if you disagree, no need to formalize): enemies are kamikaze; train units are not damageable in Slice 1 (only jostled) so we isolate motion + attack feel; lose = freeze + "game over" text.

The one decision that actually changes train.lua's shape:

AskUserQuestion 

Your questions have been answered: "How should the train hold formation as it follows the waypoint loop? (This is the main thing that shapes train.lua; both are dynamic, so both get the organic enemy-jostle you want.)"="Head + followers, like in SNKRX. However, before you get started on anything, let's do this in a very piecemeal basis. You're preparing to do everything at once, let's not do that, wait for my instructions on what to do at each step.". You can now continue with these answers in mind.

Got it — head + followers (SNKRX conga), logged. And point taken: I was lining up the whole slice at once. I'll drop that and go strictly step-by-step — one small piece, you test, you tell me the next one. I won't build ahead of your instructions, and the Slice 1 brief above is just a map, not a queue I'll churn through.

So I'll wait for you to call the first step.

If it helps to have something to react to: the smallest meaningful starting point I'd suggest is just the loop — loop_points + a single rectangle unit steering around it via follow_path, drawn on screen, nothing else (no followers, no enemies, no combat, no core). That isolates "does a steered dot tracking waypoints look right and loop cleanly" before anything stacks on it.

But that's only a suggestion — tell me what you want step 1 to be.

Yes, let's do that as step one. Points that for a loop, a single rectangle unit steering along them. Draw the points visually, and also make sure the unit has a "push" function available on hit, and that it's tied to a key. I want to be able to push train segments and see them go back to the path, to make this as cool looking as natural as it can be. In the next step, the conga logic has to also make following units feel good and natural as they follow other pushed units.

Approved — step 1 it is, with the push test built in. Before I write anything I'll post a focused brief (per the brief-before-code rule), but first let me ground the push + steering idiom in the actual code so the brief is accurate — I want to reuse the seeker's :push rather than invent one, and match the scene skeleton.

Read (E:\a327ex\mini-looper\snkrx\seeker.lua)

1    --[[
2     seeker.lua — basic chase-the-player enemy.
3   
4     Faithful port of v1's seeker (~main.lua 9203-9514). Same silhouette
5     (14×6 rounded rect), same hp pool, same speed range, same steering
6     recipe (seek + wander + separate combined inside max_force=200),
7     same spawn/hit/death FX, same sounds. The bytepath-era pack /
8     rarity / modifiers system (yellow/blue specials, slow_aura,
9     explode_on_death) is intentionally NOT ported here — Invoker's
10    loot/modifier layer is going to live higher up the stack; the
11    seeker itself stays mechanical.
12  
13    Differences from v1 that aren't cosmetic:
14      • Procedural Anchor 2 patterns: plain field timer/spring/collider,
15        explicit update of each sub-module, `cached_enemies` is replaced
16        by iterating the seekers[] array for steering_separate.
17      • `cyclone_spin` death-spin parameter dropped (no cyclone ability
18        yet — spin defaults to 0, which matches v1's effective behavior
19        when nothing has tagged the seeker with cyclone). Re-add when
20        Cyclone lands.
21      • `damaged_by_area` tick-rate guard dropped — fireball is the only
22        area right now and it's instant, so re-hits per cast can't happen.
23        Bring back the guard when duration zones land.
24      • Push knockback timer-name bug fixed. v1 reuses the name 'push'
25        for both the 0.15s flash-off and the 0.5s pushed-state-off
26        timers, so the second registration cancels the first and the
27        seeker stays white-flashed forever after a push. We use
28        distinct names ('push_flash' / 'push_end') so both fire.
29  ]]
30  
... [343 more lines]

Read (E:\a327ex\mini-looper\main.lua)

1    --[[
2     snkrx-template / main.lua — clean reference scene.
3   
4     This is your file. It is a complete, minimal scene: a player you can
5     move (WASD / arrows), the five-layer render stack, a camera, physics,
6     the update / draw skeleton, AND the UI render pipeline — all wired
7     and ready, but firing no attacks and drawing no UI widgets. Read it
8     top to bottom; it is the contract you build on.
9   
10    TWO TOOLKITS, ONE REQUIRE.  `require('snkrx')` pulls in BOTH:
11  
12      snkrx/<carrier>.lua     attack toolkit — projectile / area / beam
13                              / flicker / prop, the effect draw-shader
14                              stack, fx, sounds, example entities.
15      snkrx/ui/<module>.lua   UI toolkit — panel / button / slot / bar /
16                              tabs / checkbox / radio / slider /
17                              list_row / card / text_input / modal /
18                              bracket_tag / stat_chip / pips / ...
19  
20    Both are plain, readable Lua, not opaque modules — open the files.
21  
22    ADDING AN ATTACK.  Every carrier already has its object list and its
23    update / draw loop wired below. To add an attack:
24      1. bind a key in the INPUT section,
25      2. call the carrier's spawn_* helper on that press inside update()
26         — see the ATTACKS comment block there.
27    Nothing else: no new list, no new loop.
28  
29    DRAWING UI.  The UI toolkit is immediate-mode: call widget functions
30    in update() and they queue draws onto `ui_layer`. The render pipeline
... [354 more lines]

Grounded now. The key find: seeker:push(angle, force, duration) is exactly the idiom you want — it sets a pushed flag (steering is bypassed while pushed), bumps linear damping so the impulse visibly drains, adds a tumble-spin that tweens back to 0, and arms a push_end timer that restores damping and clears the flag. When the flag clears, normal steering resumes and pulls the unit back. So "shove it, watch it steer home" is a near-verbatim reuse, not new code. Here's the step-1 brief.

⛔ DESIGN BRIEF — Step 1: loop + one steered unit + push-on-key

Scope: a visible loop of points, ONE rectangle unit steering around it via follow_path, and a key that shoves the unit so we can watch it recover. No followers, enemies, combat, or core. Two new files + small edits to main.lua.

loop.lua

train.lua

main.lua edits

Small choices to confirm (override in your reply):

  1. Push test direction = random (vs toward/away from mouse, vs outward from center).
  2. Removing the player avatar (vs keeping it around).
  3. Start params (speed 140 / force 400 / seek 10 / push 10) — pure feel knobs, we tune live once it's on screen.

That's the whole step. I'll wait for your go (or tweaks) before writing — then it's the two files + the main.lua edits, and you run it.

Go ahead, give me some simple UI to change speed, seek and push forces.

On it. The brief's agreed; the live-tuning UI is the one addition, so let me read the exact ui_slider API and layout helpers so I wire it correctly, plus confirm a couple of draw signatures.

Grep (function ui_slider|function ui_label|function ui_text\b|function ui_panel|function ui_stat_chip)

mini-looper\snkrx\ui\widgets.lua:759:function ui_slider(opts)
mini-looper\snkrx\ui\primitives.lua:62:function ui_panel(opts)
mini-looper\snkrx\ui\primitives.lua:89:function ui_text(opts)
mini-looper\snkrx\ui\primitives.lua:237:function ui_label(opts)
mini-looper\snkrx\ui\primitives.lua:391:function ui_stat_chip(opts)

Grep (layer_circle\b|layer_line\b|layer_circle_line\b)

13:layer_circle(layer, x, y, radius, color)
14:layer_circle_line(layer, x, y, radius, color, line_width?)
15:layer_line(layer, x1, y1, x2, y2, width, color)

Read (E:\a327ex\mini-looper\snkrx\ui\widgets.lua)

759  function ui_slider(opts)
760   local r       = opts.rect
761   local id      = opts.id
762   local ed      = opts.spec
763   local track_h = opts.track_h or 5
764   local knob_d  = opts.knob or 12
765   local knob_r  = knob_d/2
766 
767   -- Knob travel is inset by the knob radius so it never clips the rect.
768   local travel = r.w - knob_d
769 
770   -- Interaction: press grabs, drag tracks the cursor, release lets go.
771   local value   = math.clamp(opts.value or 0, 0, 1)
772   local hovered = false
773   if id then
774     ui_claim_hot(id, r)
775     hovered = ui_is_hot(id)
776     if hovered and mouse_is_pressed(1) then
777       ui_state.active_id = id
778       ui_state.focus_id  = id
779       ui_juice_pull(id, 0.2, r)
780     end
781     if ui_state.active_id == id then
782       local mx = mouse_position()
783       value = math.clamp((mx - r.x - knob_r)/travel, 0, 1)
784       if mouse_is_released(1) then ui_state.active_id = nil end
785     end
786     ui_juice_hover(id, hovered, nil, r)
787   end
788 
... [40 more lines]

Read (E:\a327ex\mini-looper\snkrx\ui\primitives.lua)

62   function ui_panel(opts)
63    local r    = opts.rect
64    local fill = opts.bg or panel_fill
65    local rad  = opts.radius or 3
66    local ed   = opts.spec
67  
68    if opts.border then
69      local bw = opts.border_width or 1
70      ui_rrect(r.x, r.y, r.w, r.h, rad, opts.border, ed)
71      ui_rrect(r.x + bw, r.y + bw, r.w - 2*bw, r.h - 2*bw,
72        math.max(0, rad - bw), fill, ed)
73    else
74      ui_rrect(r.x, r.y, r.w, r.h, rad, fill, ed)
75    end
76    return ui_ret(r, {})
77  end
78  
79  --[[
80    ui_text(opts)
81  
82    A single line of text aligned within a rect. opts: rect, text, font
83    (ui_font_body), color (text), align_h ('left'/'center'/'right'),
84    align_v ('top'/'center'/'bottom'), spec.
85  
86    The draw position is pixel-snapped — fractional glyph quads drop a
87    vertical pixel column under the rough filter.
88  ]]
89  function ui_text(opts)
90    local r     = opts.rect
91    local str   = opts.text
... [80 more lines]

Read (E:\a327ex\mini-looper\snkrx\ui\rect.lua)

1    --[[
2     ui/rect.lua — RectCut layout primitive for the UI toolkit.
3   
4     A rect is a plain table {x, y, w, h}. Three families of operations:
5   
6       cut_*(r, n) — mutates r (eats n pixels from one side), returns the eaten slice.
7       get_*(r, n) — pure: returns a slice of r without mutating.
8       add_*(r, n) — pure: returns a new rect adjacent to r (extends outward).
9   
10    Plus utilities: contract / expand (inset / outset), center (place a w×h
11    rect centered inside another), split_h / split_v (divide into n equal parts).
12  
13    Origin: cut/get/add are the Halt RectCut pattern. Cuts are destructive on
14    the parent so successive cuts walk the rect. Canonical idiom:
15      local topbar = rect_cut_top(r, 24)   -- r is now the body below the topbar
16      local botbar = rect_cut_bot(r, 22)   -- r is now the body between bars
17  
18    Verbatim from the Anchor App (Anchor2/app/rect.lua) — proven, unchanged.
19  ]]
20  
21  function rect_new(x, y, w, h)
22    return {x = x, y = y, w = w, h = h}
23  end
24  
25  -- cut_*: mutate r (eat n from one side), return the eaten slice.
26  function rect_cut_left(r, n)
27    local s = {x = r.x, y = r.y, w = n, h = r.h}
28    r.x = r.x + n
29    r.w = r.w - n
30    return s
... [71 more lines]

The API's clear: ui_slider({rect, id, value=0..1}) returns {value} (caller-owned state), and seeker:push is exactly reusable. Writing the two new files now.

Write (E:\a327ex\mini-looper\loop.lua)

File created successfully at: E:\a327ex\mini-looper\loop.lua (file state is current in your context — no need to Read it back)

Write (E:\a327ex\mini-looper\train.lua)

File created successfully at: E:\a327ex\mini-looper\train.lua (file state is current in your context — no need to Read it back)

Now the main.lua edits.

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the two draw-block edits (game layer + F2 debug overlay).

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

All edits applied. Now syntax-check the three files with lua54.exe (parse-only — undefined runtime globals are fine).

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Done — all three files parse clean. Here's what landed and how to test it.

What's in step 1

Test it (run it your way — I didn't):

  1. You should see the grey-dot ellipse and one ~10px square gliding around it.
  2. Top-left panel: three sliders — SPEED (0–300), SEEK (2–40), PUSH (0–30) — each showing its live value. Drag to tune.
  3. SPACE shoves the unit in a random direction — watch it tumble + flash, then steer back onto the loop. Spam it from different angles.
  4. F2 toggles the collider overlay (now the unit's box).

What to feel for / how the knobs behave:

WASD is inert now (no avatar) — that's expected.

Once the motion + push feel right to you, step 2 is the conga: units 2..n following the unit ahead, tuned so followers trailing a pushed unit also read naturally. Tell me when you're happy with this, or what to adjust.

After being pushed, instead of going back to original point it was going to, it goes back to the closest point to it when the push ends. Make the push direction always face inwards, as that's mostly what will be happening, since enemies come from outside. Make the path of points less regular, so not a perfect oval, more twists and turns, some abrupt changes in direction, etc, so I can see how it behaves in more cases.

Three changes: (1) on push-end, rejoin at the nearest loop point instead of the old target; (2) push always fires inward (toward center), simulating an enemy hitting from outside; (3) swap the clean oval for a fixed irregular track with bulges, sharp turns, and concave notches. Rewriting loop.lua and patching train.lua + the scene call.

Write (E:\a327ex\mini-looper\loop.lua)

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Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\main.lua)

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. Changes are in:

  1. Push rejoin → nearest point. When the push timer ends, the unit now re-acquires path_index via nearest_loop_index(current pos), so it rejoins the road at the closest waypoint and continues forward — instead of steering back to the (possibly now-behind) point it was originally heading for.
  2. Push is inward. train_push_head now shoves toward the loop center (math.angle_to_point(unit, center)) — the direction an enemy from outside would push it. (The internal :push still takes any angle, so enemy hits later will pass their own contact angle.)
  3. Irregular track. Replaced the oval with build_loop_track — 18 points, even angular spacing but a hand-authored per-point radius array (0.50 … 1.22) giving bulges, near-straights, abrupt turns where adjacent radii jump hard, and concave inward notches. It's angle-sorted so it can't self-intersect. Centered slightly down-right (+30, +15) so it clears the tuning panel.

Test it:

Two things to tell me after you watch it:

Is there a way to make the unit's movement more smooth? Right now whenever it looks into a new point it changes to that direction abruptly, perhaps we could use one of the lerp functions to do it over time. Remember to use the math module dt lerp functions with p, t as arguments, those are correct, if you do it manually it will be wrong.

Good question — the facing (self.r) is already eased, but the travel direction still snaps because the steering force points hard at each new waypoint. I'll ease the velocity itself. First let me confirm the exact math.lerp_dt signature so I use the (p, t, dt, ...) form you flagged, not a manual lerp.

Grep (function math.lerp_dt|function math.lerp_angle_dt|lerp_dt\s=|lerp_angle_dt\s=)

mini-looper\anchor\math.lua:79:function math.lerp_dt(p, t, dt, source, destination)
mini-looper\anchor\math.lua:167:function math.lerp_angle_dt(p, t, dt, source, destination)

Read (E:\a327ex\mini-looper\anchor\math.lua)

60     Framerate-independent linear interpolation.
61  
62    Usage:
63      x = math.lerp_dt(0.9, 1, dt, x, target)   -> covers 90% of distance in 1 second
64      x = math.lerp_dt(0.5, 0.5, dt, x, target)  -> covers 50% of distance in 0.5 seconds
65  
66    Parameters:
67      p           - Percentage of distance to cover (0.9 = 90%)
68      t           - Time in seconds to cover that percentage
69      dt          - Delta time
70      source      - Current value
71      destination - Target value
72  
73    Returns: new value moved towards destination
74  
75    Behavior:
76      - Exponential approach: value gets closer but never quite reaches target
77      - Useful for smooth camera follow, UI animations, etc.
78  ]]
79  function math.lerp_dt(p, t, dt, source, destination)
80    return math.lerp(1 - (1 - p)^(dt/t), source, destination)
81  end
82  
83  --[[
84    Framerate-independent damping (decay toward zero).
85  
86    Usage:
87      x = math.damping(0.9, 1, dt, x)   -> after 1 second, x will be 10% of its initial value
88      x = math.damping(0.5, 0.5, dt, x)  -> after 0.5 seconds, x will be 50% of its initial value
89  
... [90 more lines]

[Request interrupted by user]

Show me how exactly self.r is already eased.

It's this line in train_unit:update, in the not-pushed branch (train.lua):

    self.collider:apply_force(fx, fy)
    local vx, vy = self.collider:get_velocity()
    vx, vy = math.limit(vx, vy, train_max_speed)
    self.collider:set_velocity(vx, vy)
    self.r = math.lerp_angle_dt(0.99, 0.1, dt, self.r, math.atan(vy, vx))   -- <-- here

Mapping it to the definition you just looked at — math.lerp_angle_dt(p, t, dt, source, destination):

Then below, self.collider:set_angle(self.r) applies it to the body.

Two reasons this doesn't smooth what you're seeing:

  1. It only eases the facing, not the travel direction. self.r is the rotation the box is drawn/oriented at. The actual path the unit traces is its velocity, which is driven by apply_force toward the current waypoint and hard-clamped to train_max_speed. When follow_path advances to a new point, the seek target jumps, so the velocity kinks — and self.r is just chasing that already-kinked velocity.

  2. Even the facing ease is near-instant at 0.99 / 0.1, so it tracks the snap closely anyway.

So to smooth the movement (the traced path), the ease has to go on the velocity vector — that's what I was setting up: lerp the live velocity toward the desired-toward-waypoint velocity with math.lerp_dt(p, t, dt, …), using a gentler p/t than 0.99/0.1. Want me to proceed with that?

We just need to change the 0.99/0.1 values then, give me two more UI sliders tracking those two values.

Got it — these two sliders will tune the existing self.r ease (the 0.99/0.1). One honest flag, then I'll comply: this eases the box's facing/orientation, not the path it traces — so it changes how fast the square re-aligns to its travel direction at corners (visible as the square↔diamond orientation shifting), but it won't round off the cornering of the path itself. With that understood, here are the edits.

Edit (E:\a327ex\mini-looper\train.lua)

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[Request interrupted by user]

Ah, then it was a mistake on my part, I'd like to change the path itself, not just the angle.

Ah, that flips it back to the better approach — ease the velocity (which is the path), keep facing as a fixed light ease. So the two sliders will now control the path smoothing. Reworking train_unit:update and repurposing the two globals.

Here's the change:

Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\train.lua)

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Now update the train.lua docblock to list all five knobs, and add the two path-ease sliders to the main.lua tuning panel (bumping its height and giving the tuner a decimal-format option).

Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\main.lua)

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. The smoothing now applies to the path, not the facing:

Test it:

Two interactions to watch (both tunable, that's the point):

Show me the comments for math.lerp_dt again so I can see how it describes p and t exactly.

Here's the docblock for math.lerp_dt verbatim from anchor/math.lua (lines 59–81):

  Framerate-independent linear interpolation.

  Usage:
    x = math.lerp_dt(0.9, 1, dt, x, target)   -> covers 90% of distance in 1 second
    x = math.lerp_dt(0.5, 0.5, dt, x, target)  -> covers 50% of distance in 0.5 seconds

  Parameters:
    p           - Percentage of distance to cover (0.9 = 90%)
    t           - Time in seconds to cover that percentage
    dt          - Delta time
    source      - Current value
    destination - Target value

  Returns: new value moved towards destination

  Behavior:
    - Exponential approach: value gets closer but never quite reaches target
    - Useful for smooth camera follow, UI animations, etc.
function math.lerp_dt(p, t, dt, source, destination)
  return math.lerp(1 - (1 - p)^(dt/t), source, destination)
end

So exactly:

Together they read as "cover p of the distance every t seconds," and because it's the exponential form 1 - (1 - p)^(dt/t), it's a smooth asymptotic approach — it keeps getting closer but never exactly arrives.

A consequence worth noting for the sliders: p and t aren't independent knobs — only their ratio matters for the rate. (0.9, 0.1) and (0.99, 0.2) and (0.684, 0.05) all decay at the same speed (same half-life). So the two sliders overlap in effect; if you want one clean "smoothing" dial, the convention is to fix p (say 0.9) and vary t alone — bigger t = slower catch-up = rounder, looser path.

The current approach has decreasing p (as well as increasing t) as decreasing the total velocity of the train, which is unintuitive but it does the job of making the turns more smooth. Do you think the same smoothness could be achieved without affecting the overall velocity or is that unlikely to be possible? I think it's unlikely, but maybe you can think of something. Values 0.7 for p and 0.3 for t at 300 speed seem like good defaults. You can comment/hide the UI for now and fix on those values. Actually, fix the UI to a toggable key, and start it toggled off. And tell me about the velocity question, however don't act on it before I can see what you reason.

Got it. I'll apply the defaults (p=0.7, t=0.3, speed=300) and move the tuning panel onto an F1 toggle that starts off — but I'll hold off entirely on the velocity-decoupling idea until you've read the reasoning below.

Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\main.lua)

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Done and syntax-clean. F1 toggles the tuning panel (starts hidden); when hidden the train runs on the fixed defaults p=0.70, t=0.30, speed=300. SPACE still pushes inward; F2 still toggles colliders.

The velocity question

Your intuition that it's "unlikely" is actually too pessimistic — decoupling smoothness from speed is easy and standard. Here's the reasoning.

Why they're coupled right now. We smooth by lerping the velocity vector itself: v = lerp_dt(p, t, dt, v, desired) -- desired = dir_to_waypoint * max_speed A vector carries two things at once — direction and magnitude — and the lerp blends both. When v and desired point different ways (i.e. mid-turn), the straight-line blend between two points on the "speed circle" cuts through the circle, so the result is shorter than max_speed. In steady-state turning the velocity settles at a lag angle behind desired, and the push along its own heading is only max_speed·cos(lag) — so the more lag (lower p / higher t / sharper turn), the slower it goes. The slowdown isn't a side bug; it's baked into "blend the whole vector."

How to decouple. Smooth the direction alone and keep the magnitude pinned: move_r = lerp_angle_dt(p, t, dt, move_r, angle_to_waypoint) -- ease the heading v = (cos(move_r), sin(move_r)) * max_speed -- speed is always max_speed Now p/t govern only how fast the heading swings; speed is constant by construction. (A cheaper variant: keep the current vector lerp but normalize(v)*max_speed at the end — same idea, though the magnitude feedback slightly shifts the effective rate so you'd retune p/t. The angle method is the clean one.)

So: yes, fully possible, and not hacky — it's the textbook "separate heading from throttle" move.

But here's the part worth weighing before you ask for it: the speed dip you're calling unintuitive is arguably good game-feel, not a defect. It means the train automatically eases off through sharp turns and runs full-tilt on straights — exactly how a vehicle reads. Decoupling to constant speed makes the motion more uniform/robotic and makes it overshoot sharp corners more (it never slows, so it covers more ground while still mid-turn → wider arcs, more orbiting risk at the notches). The coupled version is partly self-correcting there.

If you want both — constant base speed but a deliberate slow-in-turns — you'd add it back explicitly: scale speed by heading error or path curvature (speed = max_speed * (1 - k*angle_error)). That's a third knob, but it's a designed slowdown you control, independent of the smoothing dial.

My honest take: the cleanest design is the decoupled heading-smoothing (so the SMOOTH knob never touches speed) plus an optional explicit "corner slowdown" knob if you decide the deceleration feels good. That gives you two orthogonal controls instead of one entangled one. But it's a real feel change, so I've left it untouched — tell me which way you want to go.

Yes, let's try both your changes, giving me the additional knob.

Both changes. Let me check whether the math module already has an angle-difference helper before I hand-roll the corner-slowdown's "how sharp is this turn" term.

Grep (function math.(angle_delta|angle_diff|shortest_angle|angle_dist|angle_between|to_angle))

No matches found

Grep (^function math.)

55:function math.lerp(t, source, destination)
79:function math.lerp_dt(p, t, dt, source, destination)
98:function math.damping(p, t, dt, v)
120:function math.loop(t, length)
142:function math.lerp_angle(t, source, destination)
167:function math.lerp_angle_dt(p, t, dt, source, destination)
184:function math.sign(value)
203:function math.length(x, y)
222:function math.clamp(value, min, max)
250:function math.remap(value, old_min, old_max, new_min, new_max)
269:function math.angle(x, y)
287:function math.angle_to_point(x1, y1, x2, y2)
304:function math.distance(x1, y1, x2, y2)
323:function math.normalize(x, y)
345:function math.direction(angle)
363:function math.rotate(x, y, angle)
387:function math.reflect(angle, normal_x, normal_y)
415:function math.snap(value, grid)
437:function math.limit(x, y, max)
448:function math.linear(t) return t end
451:function math.sine_in(t)
457:function math.sine_out(t)
463:function math.sine_in_out(t)
469:function math.sine_out_in(t)
477:function math.quad_in(t) return t*t end
479:function math.quad_out(t) return -t*(t - 2) end
481:function math.quad_in_out(t)
490:function math.quad_out_in(t)
501:function math.cubic_in(t) return t*t*t end
503:function math.cubic_out(t)
... [30 more lines]

No angle-diff helper, so I'll compute the shortest gap with math.loop (a plain angle calc — fine to hand-roll; the dt-lerp warning doesn't apply). Applying both changes:

Decouple speed from smoothing — ease the heading (move_r) via lerp_angle_dt, then apply a fixed-magnitude velocity. New CORNER knob — scales an explicit slow-in-turns based on how far the heading still is from the waypoint.

Edit (E:\a327ex\mini-looper\train.lua)

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Now the main.lua panel: bump height, widen SPEED range (300 was pinned at max), and add the CORNER slider.

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

All clean. Both changes are in:

Speed/smoothing decoupled. train_unit:update now eases the heading (self.move_r) toward the waypoint with lerp_angle_dt(train_turn_p, train_turn_t, …), then applies velocity at a fixed magnitude. So EASE P / EASE T now change only how round the path is — they no longer sag the speed. self.r follows move_r directly (no low-speed jitter).

New CORNER knob. Speed is scaled by 1 - CORNER·(heading_gap/π), floored at 0.1× so it never stalls. CORNER = 0 → dead-constant speed; higher → the explicit slow-in-sharp-turns feel, now a deliberate dial instead of an accident of the math.

Defaults on the fixed values: speed 300, EASE P 0.70, EASE T 0.30, CORNER 0.50. Panel is 6 sliders now, behind F1 (starts hidden). SPEED slider goes 0–500 so 300 isn't pinned at the end.

Test it:

Two honest notes:

Depending on the settings, sometimes the train gets stuck circling a point without ever being able to get close to it enough so the next point triggers, this happens because its turn rate is never high enough that it can actually go closer to the point, so it just circles it endlessly. How would you suggest fixing this without relying on changing the settings?

The root cause is structural: advancement fires on one condition only — "within seek_distance of the target point." So if the turn rate can't bring the unit inside that radius, it settles into a stable orbit and the trigger never fires. Any fix that's settings-independent has to make advancement not depend on actually reaching the point.

Here's how I'd think about it:

Recommended — advance when you've drawn level with / passed the point, not just when you're near it. Add a second trigger alongside the proximity check: advance when the target falls behind the unit's heading:

dot(target - pos, heading_dir) < 0   -- target is now beside/behind me → move on

Geometrically: "I'm as far along as I'm going to get against this point — stop chasing it, take the next one." An orbit around a point necessarily swings that point abreast and then behind the unit within half a loop, so the dot-product goes negative and it advances — it physically cannot stay stuck, at any speed/ease/seek combination. Two more bonuses: it's ~2 lines in the existing advance check (keep seek_distance for the crisp head-on case, add this for everything else), and it makes corner-cutting consistent — the unit advances as it draws level with the apex, which is exactly the smooth behavior the easing already wants.

One edge I'd watch: right after a push we set path_index to the nearest point, and the heading might briefly point away from it → instant "it's behind me" → skip to the next point. Harmless (it just targets the following point), but I'd guard it if it ever looks like a hiccup.

Heavier alternative — pure-pursuit "carrot." Instead of chasing fixed waypoints, steer at a point a fixed distance ahead along the path. The target is always moving forward, so orbiting is structurally impossible, and you get look-ahead corner-smoothing for free. But it needs a closest-point-on-polyline search + per-segment lengths each frame — i.e. it reintroduces a bit of the path-length bookkeeping you deliberately dropped. More robust in theory, more machinery in practice, and it overlaps with the heading-ease smoothing we already have.

I'd go with the dot-product gate — it's the minimal change that provably kills the orbit and fits the current discrete-waypoint model. Which way do you want it?

AskUserQuestion 

Your questions have been answered: "How should I fix the orbit-stuck problem?"="Dot-product gate". You can now continue with these answers in mind.

Implementing the dot-product gate. Two edits to train.lua: the advance check gets the "passed it" test, and I'll also re-aim move_r at the rejoin point on push-end so the gate doesn't instantly skip it (the edge I flagged).

Edit (E:\a327ex\mini-looper\train.lua)

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Edit (E:\a327ex\mini-looper\train.lua)

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. The fix is in:

Test it: push the settings into the combo that used to trap it — e.g. high SPEED + high EASE T (slow turning) + small SEEK. Before, it'd lock into an endless circle around a sharp notch; now it should sweep wide, draw level with the point, and move on to the next one instead. Normal head-on arrivals still snap crisply via the proximity check, so nothing changes about the good cases.

Worth watching for: on very loose turning it'll now visibly cut corners (advancing as it draws level with the apex rather than reaching it) — that's the intended consequence, but if any corner gets cut harder than you'd like, that's a SEEK/EASE feel call, not the orbit bug returning.

Change back, this makes it too easy for it to ignore points altogether. I'll just choose good defaults that make the turn problem unlikely to happen.

Reverting both — the advance check goes back to proximity-only, and I'll drop the push-end heading re-aim I'd added to support the gate (so train.lua is exactly back to the pre-gate state you liked). You'll pick defaults that keep the turn radius tight enough to avoid orbiting.

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Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Reverted and clean. train_unit:update is back to proximity-only advancement (within seek_distance → next point), and push_end just sets path_index to the nearest point without touching move_r. So the orbit behavior is back as it was — you'll keep it from happening by choosing defaults (a tight enough turn rate vs speed/seek) rather than a structural gate.

The two new feel knobs from earlier are still in place and fixed (panel hidden behind F1): EASE P/T smooth the path without affecting speed, and CORNER scales the slow-in-turns. Tune SPEED ↔ EASE T ↔ SEEK together to find the band where it never orbits, then lock those in as the defaults.

OK. Default values: speed = 100, seek = 15, p = 0.7, t = 0.3, corner = 0.4.

Trivial value updates. Applying the new defaults in train.lua (p and t are already 0.70/0.30, so just speed, seek, and corner change).

Edit (E:\a327ex\mini-looper\train.lua)

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Done. Final defaults baked into train.lua (panel stays hidden behind F1 until you open it to tweak):

Knob Default
SPEED 100
SEEK 15
EASE P 0.70
EASE T 0.30
CORNER 0.40

PUSH is still 10. Step 1 is locked in: a single unit smoothly tracking the irregular loop, inward push with nearest-point rejoin, and a tunable feel panel on F1. Whenever you've confirmed the motion feels right, the next step is the conga — units 2..n following the unit ahead, tuned so followers behind a pushed unit also trail naturally.

Yes, let's add more units now.

Moving to the conga. This is a non-trivial change, so here's the brief before I touch code.

⛔ DESIGN BRIEF — Step 2: the conga (followers)

Goal: units 2..n trail the unit ahead, forming a snake that traces the loop and reacts naturally when any unit is pushed.

Movement model — head unchanged, followers chase a "slot." The head (the unit with no leader) keeps its exact current logic: waypoint walk + heading-ease + corner slowdown + fixed speed. A follower instead targets a slot = a point train_spacing behind its leader along the leader's heading. Aiming behind-along-heading (rather than straight at the leader) keeps the slot on the road — followers hug the path instead of chord-cutting across corners. Each follower:

Because speed scales with slot distance, corner-slowdown and pushes propagate down the chain for free — when the leader slows, its slot advances slower, so the follower slows too.

Who's my leader. train_update already walks the ordered train_units list, so it just passes each unit its leader: u:update(dt, train_units[i-1]). train_units[0] is nil → unit 1 is the head. Role is decided by "do I have a leader" — no stored refs (order is stable; nothing dies in step 2).

Push reaction. :push is unchanged and shared by every unit. When a unit is shoved, the ones behind it are chasing its slot, which moves with it → they get tugged and ease back as it recovers; the kink propagates and heals. That's the "followers react to a pushed unit" feel you wanted.

Spawn pre-strung. train_build(n) spawns unit i at loop_points[1] offset (i-1)*spacing back along the initial heading, so the train starts as a line behind the head instead of all stacked on one point.

main.lua wiring.

New globals: train_spacing ≈ 16, train_follow_gain ≈ 10, train_follow_max ≈ 250 (all live-tunable).

Choices I've defaulted (override in your reply):

  1. Count: fixed at 5 for now (vs a rebuild-on-key count control).
  2. Push test: random unit (vs keep SPACE=head + a second key for a middle unit).
  3. No train↔train collision/separation yet — slot-chasing shouldn't let them overlap much; I'll add separation only if they clump in tight corners.

One honest note on the tradeoff I picked: slot-chasing traces the road but, like any proportional follow, leaves a small steady-state lag (gap ≈ spacing + speed/gain), so the snake stretches a touch on fast straights and compresses in slow corners — which reads as natural chain tension. If you'd rather have rigid, exact spacing that perfectly traces the head's path, that's the breadcrumb/trail approach instead — but it's non-physical (a pushed middle unit wouldn't tug the chain), which is why I'm not recommending it here.

Wait for your go or tweaks.

Go ahead.

Approved — implementing the conga. Editing train.lua (docblock, new knobs, head/follower branch, pre-strung spawn, leader passing, random-push test) and main.lua (5 units, random push, two new sliders).

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now main.lua: 5 units, random-push call, and the two new sliders (panel grows to 8).

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

All clean. Step 2 is in:

Test it:

Two things to watch and tell me about:

When the conga feels right, pick good SPACING/GAIN defaults (like we did for the head) and we'll lock them in. After that, the natural next step is enemies — center-seeking seekers the train auto-attacks — but that's a fresh brief when you're ready.

I set spacing and gain at the lowest values possible ($ and 2) and it looks very off still. High gain makes the train spiral out of control, so gain values have to be low. I want to try lower values but the UI doesn't let me. We might need to change the approach if I can't make it look right. But the pushing and the way other units follow the pushed unit does work well and it's how I imagined it.

Good data point — and your instinct is right that the model might be the issue. Let me first widen the sliders so you can keep experimenting (you asked, it's trivial), then diagnose why there's no good value, then propose the fix.

Widening the ranges — GAIN down to 0.1 (with 2-decimal readout), SPACING down to 0:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

Exit code 1
E:\a327ex\Anchor\reference\love-compare\tools\lua54.exe: (command line):1: unexpected symbol near 'and'

That error is in my test one-liner, not the file. Re-running the proper check:

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Syntax clean — GAIN now drags to 0.1 (2-decimal), SPACING to 0, so you can explore. But here's why I think you'll hit the same wall, and the fix:

Why there's no good value

The follower speed is a pure proportional controller: speed = distance_to_slot × GAIN. That has a built-in lag-vs-stability tradeoff with no sweet spot:

Same knob trades lag for instability, so neither end looks right. Your instinct to change the approach is correct.

⛔ DESIGN BRIEF — fix: velocity feedforward

Keep everything you liked (slot-chase + heading-ease → the push/follow reaction stays exactly as is). Change only the follower speed formula:

speed = leader_speed + dist_to_slot × GAIN      -- leader_speed = |leader velocity|

It's a one-line change to the follower branch (speed = math.length(leader_vel) + d*train_follow_gain, still clamped to train_follow_max). The structure, the heading-ease, and the push behavior you already like are untouched.

One risk to watch: during a push the pushed unit's own speed spikes (the impulse), so its followers' feedforward briefly spikes too — they'll chase a bit more eagerly than now. I think it'll still read as the tug-and-settle you liked (maybe even better), but if it gets too tight we can feed forward the leader's nominal cruise speed instead of its live speed. Easy to switch.

Want me to apply it? (And I'd re-default GAIN to something low like 6–10 once feedforward is carrying the pace.)

The current gain value at 0 simply makes followers not actually follow because they're too slow. Will your proposed change fix that?

Yes — directly. That "GAIN 0 = frozen" is the same root cause, and it's the clearest illustration of why feedforward fixes it.

Right now speed = distance_to_slot × GAIN, so GAIN is the only thing that makes a follower move at all. At GAIN 0 → speed 0 → frozen. GAIN is doing two jobs at once: "be able to keep up" and "hold tight spacing," which is exactly why no single value works.

With the feedforward formula speed = leader_speed + distance_to_slot × GAIN:

So feedforward demotes GAIN from "make them move" to "how stiffly they snap to spacing." The whole [frozen ↔ spiral] range collapses into a usable band, and even the extremes are sane: GAIN 0 = loose-but-following, high GAIN = stiff-but-stable.

Want me to apply it?

Yes.

Applying the feedforward change to the follower speed in train.lua (plus the comment/docblock so the docs stay accurate).

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. The follower speed is now leader_speed + slot_distance × GAIN (clamped to train_follow_max). What changed in feel:

Default GAIN is 10 (already in the low/stable band) and SPACING 16.

Test it: open F1 and sweep GAIN from 0 upward — you should feel it go from a loose, stretchy chain to a tight, stiff one, with a usable band in between and no spiral at the top. Set SPACING to the gap you want; it should hold that gap on straights and in corners now. Then confirm the push still tugs-and-settles the way you liked.

Once it looks right, give me good SPACING/GAIN defaults to lock in (same as we did for the head knobs), and we're done with the train movement — enemies would be the next brief whenever you want.

Spacing 0 and gain 0.10 (lowest it can go) still has units with some considerable spacing between them, not really 0.

[Request interrupted by user]

I think the issue with the model is that, beyond not being able to control the spacing accurately, units further back tend to overshoot, because they're following a degraded version of the leader's path. This is theoretically necessary for us to get the push behavior we want, but it looks off and doesn't look like a proper train. A proper train, like in SNKRX, has all units following the head's path directly, but you mentioned that doing that would break the ability for units to be pushed and for units behind and in front to be pushed accordingly. Perhaps a better model for us would be actually using something like a physics chain that is lightly guided by logic, such that on push behaviors the physics chain comes into play, but on other normal cases it behaves more like the fixed conga from SNKRX. What do you think? Let's not do anything yet, just discuss it.

Your diagnosis is right — and sharper than you put it. What you're watching is a chain of low-pass filters: each follower tracks a smoothed, lagged version of its neighbor, who is itself a smoothed/lagged version of its neighbor. The filtering compounds, so by unit 5 the head's path is badly smeared — corners rounded off, spacing drifting, overshoot piling up. That's intrinsic to "each unit follows the one ahead with its own dynamics," and no amount of GAIN/SPACING tuning escapes it (which is what you've been running into).

One correction to your "theoretically necessary": the degradation is necessary in this model, not in general. Here the push-reaction and the smear come from the same mechanism (chained neighbor-following), so you can't separate them. A real chain decouples them — stiff coupling propagates a push without low-pass-smearing the cruise path. So you genuinely can have crisp-train and push-reaction; you just can't with follow-the-neighbor.

Why your instinct is correct: trail-following (SNKRX) is unidirectional by construction — every body is slaved to the head's recorded path. That's exactly why it's crisp (everyone reads the clean source, not a degraded neighbor) and exactly why it can't propagate a push. It especially can't propagate forward — a unit ahead of the pushed one already laid its trail and has no idea something behind it got shoved. So "front and back react accordingly" is fundamentally a physical-chain property; trail-following can't give it at any price. Moving to a physics chain is the right call.

The hybrid, concretely. "Physics chain lightly guided by logic" maps cleanly onto a position-based (Verlet) rope:

The real decision and its cost:

The captain's-hat question I owe you, though: this is a real model rewrite, and it's polish on how the follow looks — while we still haven't put a single enemy on screen. Is the train reading "not quite a proper train" actually blocking your ability to judge whether the game is fun, or would we be perfecting the chain before testing the thing that greenlights or kills the project? My honest lean: if the current chain reads roughly like a train at normal viewing distance, I'd put enemies + auto-attack in next (that's the actual fun-gate, beginning and end) and revisit the chain once we know the loop is worth polishing. If the off-ness genuinely wrecks the concept for you when you look at it, then the rewrite earns its place now. You're the one watching it — which is it?

It's important to get the movement correct, actually, because it changes how the game will play significantly, so we want to have a realistic view of it early on.

Nice simplification for us: because the road is a fixed loop, "where each node should sit" is a slot along the loop itself — we don't need to record the head's trail, the loop is the trail. (One static arc-length table for the loop, computed once — not the per-frame baked-path machinery we dropped.)

This, I think, is incorrect. We want only the head to lead, the others to follow the head like in SNKRX, mediated by the physics chain, and then more forcefully guided by the chain in cases of pushes. We also want to actually use Box2D joints to do this, that will make things easier and will feel more natural. This requires some Anchor work, as well as reading Box2D 3.1+ documentation so you know how to integrate it, but it's work you can do. This is a big task, so let's work on it step by step, with the Box2D integration of all required elements for the chain first. I don't remember what kind of joint it is to make chains, maybe a distance joint?

Good — you've overruled my scope concern, and you're the one who'll see whether the movement sells the game, so I'll take that as settled: movement correctness first, via real Box2D joints, done step by step starting with the engine integration.

And to confirm your joint question with reasoning: a distance joint is the right one. In Box2D v3 a distance joint connects two bodies at a target separation and (this is the key part) can be made springy — enableSpring with hertz/dampingRatio, plus optional minLength/maxLength limits. That's exactly your "lightly guided chain that gets more forceful on pushes": soft spring for the normal trailing follow, the limits/stiffness keeping spacing, and the joint network propagating a push to both neighbors for free. (Revolute joints pin links at a touching hinge — good for a literal chain of touching links, wrong for spaced-out units; weld is too rigid.)

Before I write the step-1 brief I need to see exactly how the engine wraps Box2D — version, body-handle storage, and how Lua physics calls are bound — so the brief is accurate. Investigating now.

Grep (joint|Joint)

Anchor2\engine\src\anchor.c:2

Found 2 total occurrences across 1 file.

Grep (b2CreateBody|b2DefaultBodyDef|b2BodyId|b2WorldId|b2CreateWorld|#include.box2d|#include.b2)

67:#include <box2d.h>
504:static b2WorldId physics_world = {0};
563:    b2BodyId body_a;
564:    b2BodyId body_b;
577:    b2BodyId body_a;
578:    b2BodyId body_b;
587:    b2BodyId body_a;
588:    b2BodyId body_b;
602:    b2BodyId sensor_body;
603:    b2BodyId visitor_body;
612:    b2BodyId sensor_body;
613:    b2BodyId visitor_body;
750:        ev->body_a = b2Shape_IsValid(e->shapeIdA) ? b2Shape_GetBody(e->shapeIdA) : (b2BodyId){0};
751:        ev->body_b = b2Shape_IsValid(e->shapeIdB) ? b2Shape_GetBody(e->shapeIdB) : (b2BodyId){0};
811:        ev->sensor_body = b2Shape_IsValid(e->sensorShapeId) ? b2Shape_GetBody(e->sensorShapeId) : (b2BodyId){0};
812:        ev->visitor_body = b2Shape_IsValid(e->visitorShapeId) ? b2Shape_GetBody(e->visitorShapeId) : (b2BodyId){0};
5975:    physics_world = b2CreateWorld(&world_def);
6141:    b2BodyDef body_def = b2DefaultBodyDef();
6146:    b2BodyId body_id = b2CreateBody(physics_world, &body_def);
6149:    b2BodyId* ud = (b2BodyId*)lua_newuserdata(L, sizeof(b2BodyId));
6156:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6168:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6180:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6203:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6231:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6288:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6352:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6417:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6490:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6559:    b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
... [12 more lines]

Glob (Anchor2/engine/*/.h)

Anchor2\engine\include\SDL2\begin_code.h
Anchor2\engine\include\SDL2\close_code.h
Anchor2\engine\include\SDL2\SDL.h
Anchor2\engine\include\SDL2\SDL_assert.h
Anchor2\engine\include\SDL2\SDL_atomic.h
Anchor2\engine\include\SDL2\SDL_audio.h
Anchor2\engine\include\SDL2\SDL_bits.h
Anchor2\engine\include\SDL2\SDL_blendmode.h
Anchor2\engine\include\SDL2\SDL_clipboard.h
Anchor2\engine\include\SDL2\SDL_config.h
Anchor2\engine\include\SDL2\SDL_config_android.h
Anchor2\engine\include\SDL2\SDL_config_emscripten.h
Anchor2\engine\include\SDL2\SDL_config_iphoneos.h
Anchor2\engine\include\SDL2\SDL_config_macosx.h
Anchor2\engine\include\SDL2\SDL_config_minimal.h
Anchor2\engine\include\SDL2\SDL_config_ngage.h
Anchor2\engine\include\SDL2\SDL_config_os2.h
Anchor2\engine\include\SDL2\SDL_config_pandora.h
Anchor2\engine\include\SDL2\SDL_config_windows.h
Anchor2\engine\include\SDL2\SDL_config_wingdk.h
Anchor2\engine\include\SDL2\SDL_config_winrt.h
Anchor2\engine\include\SDL2\SDL_config_xbox.h
Anchor2\engine\include\SDL2\SDL_copying.h
Anchor2\engine\include\SDL2\SDL_cpuinfo.h
Anchor2\engine\include\SDL2\SDL_egl.h
Anchor2\engine\include\SDL2\SDL_endian.h
Anchor2\engine\include\SDL2\SDL_error.h
Anchor2\engine\include\SDL2\SDL_events.h
Anchor2\engine\include\SDL2\SDL_filesystem.h
Anchor2\engine\include\SDL2\SDL_gamecontroller.h
... [71 more lines]

Confirmed it's the Box2D v3 C API (handle structs b2WorldId/b2BodyId, b2CreateWorld, b2DefaultBodyDef), with each Lua "body" being a userdata wrapping a b2BodyId. No joints currently exposed. Now I need the exact version + distance-joint API available, the Lua registration pattern, and how the collider's body is stored.

Glob (Anchor2/engine/*/box2d/.h)

Anchor2\engine\include\box2d\base.h
Anchor2\engine\include\box2d\box2d.h
Anchor2\engine\include\box2d\collision.h
Anchor2\engine\include\box2d\id.h
Anchor2\engine\include\box2d\math_functions.h
Anchor2\engine\include\box2d\types.h
Anchor2\engine\include\box2d\aabb.h
Anchor2\engine\include\box2d\arena_allocator.h
Anchor2\engine\include\box2d\array.h
Anchor2\engine\include\box2d\atomic.h
Anchor2\engine\include\box2d\bitset.h
Anchor2\engine\include\box2d\body.h
Anchor2\engine\include\box2d\broad_phase.h
Anchor2\engine\include\box2d\constants.h
Anchor2\engine\include\box2d\constraint_graph.h
Anchor2\engine\include\box2d\contact.h
Anchor2\engine\include\box2d\contact_solver.h
Anchor2\engine\include\box2d\core.h
Anchor2\engine\include\box2d\ctz.h
Anchor2\engine\include\box2d\id_pool.h
Anchor2\engine\include\box2d\island.h
Anchor2\engine\include\box2d\joint.h
Anchor2\engine\include\box2d\physics_world.h
Anchor2\engine\include\box2d\sensor.h
Anchor2\engine\include\box2d\shape.h
Anchor2\engine\include\box2d\solver.h
Anchor2\engine\include\box2d\solver_set.h
Anchor2\engine\include\box2d\table.h

Grep (B2_VERSION|#define B2_API|b2DistanceJointDef|b2CreateDistanceJoint|b2DistanceJoint_)

Found 5 files
Anchor2\engine\include\box2d\joint.c
Anchor2\engine\include\box2d\distance_joint.c
Anchor2\engine\include\box2d\types.h
Anchor2\engine\include\box2d\box2d.h
Anchor2\engine\include\box2d\base.h

Grep ({"physics[a-z]+"|lua_register(L, "physics)

9494:    lua_register(L, "physics_init", l_physics_init);
9495:    lua_register(L, "physics_set_gravity", l_physics_set_gravity);
9496:    lua_register(L, "physics_set_meter_scale", l_physics_set_meter_scale);
9497:    lua_register(L, "physics_set_enabled", l_physics_set_enabled);
9498:    lua_register(L, "physics_register_tag", l_physics_register_tag);
9499:    lua_register(L, "physics_enable_collision", l_physics_enable_collision);
9500:    lua_register(L, "physics_disable_collision", l_physics_disable_collision);
9501:    lua_register(L, "physics_enable_sensor", l_physics_enable_sensor);
9502:    lua_register(L, "physics_enable_hit", l_physics_enable_hit);
9503:    lua_register(L, "physics_tags_collide", l_physics_tags_collide);
9504:    lua_register(L, "physics_create_body", l_physics_create_body);
9505:    lua_register(L, "physics_destroy_body", l_physics_destroy_body);
9506:    lua_register(L, "physics_get_position", l_physics_get_position);
9507:    lua_register(L, "physics_get_angle", l_physics_get_angle);
9508:    lua_register(L, "physics_get_body_count", l_physics_get_body_count);
9509:    lua_register(L, "physics_body_is_valid", l_physics_body_is_valid);
9510:    lua_register(L, "physics_add_circle", l_physics_add_circle);
9511:    lua_register(L, "physics_add_box", l_physics_add_box);
9512:    lua_register(L, "physics_add_capsule", l_physics_add_capsule);
9513:    lua_register(L, "physics_add_polygon", l_physics_add_polygon);
9514:    lua_register(L, "physics_add_chain", l_physics_add_chain);
9516:    lua_register(L, "physics_set_position", l_physics_set_position);
9517:    lua_register(L, "physics_set_angle", l_physics_set_angle);
9518:    lua_register(L, "physics_set_transform", l_physics_set_transform);
9519:    lua_register(L, "physics_get_velocity", l_physics_get_velocity);
9520:    lua_register(L, "physics_get_angular_velocity", l_physics_get_angular_velocity);
9521:    lua_register(L, "physics_set_velocity", l_physics_set_velocity);
9522:    lua_register(L, "physics_set_angular_velocity", l_physics_set_angular_velocity);
9523:    lua_register(L, "physics_apply_force", l_physics_apply_force);
9524:    lua_register(L, "physics_apply_force_at", l_physics_apply_force_at);
... [32 more lines]

Now the registration pattern is clear: each physics call is a C function l_physics_X registered via lua_register(L, "physics_X", ...), and Box2D's source (incl. distance_joint.c) is vendored in include/box2d/. Let me pull the exact distance-joint API/def fields, the body-creation C pattern, and how the collider wraps a body.

Grep (b2CreateDistanceJoint|b2DestroyJoint|b2DistanceJoint_Set|b2DistanceJoint_Enable|b2Joint_|b2DefaultDistanceJointDef)

744:B2_API void b2DestroyJoint( b2JointId jointId, bool wakeAttached );
747:B2_API bool b2Joint_IsValid( b2JointId id );
750:B2_API b2JointType b2Joint_GetType( b2JointId jointId );
753:B2_API b2BodyId b2Joint_GetBodyA( b2JointId jointId );
756:B2_API b2BodyId b2Joint_GetBodyB( b2JointId jointId );
759:B2_API b2WorldId b2Joint_GetWorld( b2JointId jointId );
762:B2_API void b2Joint_SetLocalFrameA( b2JointId jointId, b2Transform localFrame );
765:B2_API b2Transform b2Joint_GetLocalFrameA( b2JointId jointId );
768:B2_API void b2Joint_SetLocalFrameB( b2JointId jointId, b2Transform localFrame );
771:B2_API b2Transform b2Joint_GetLocalFrameB( b2JointId jointId );
774:B2_API void b2Joint_SetCollideConnected( b2JointId jointId, bool shouldCollide );
777:B2_API bool b2Joint_GetCollideConnected( b2JointId jointId );
780:B2_API void b2Joint_SetUserData( b2JointId jointId, void* userData );
783:B2_API void* b2Joint_GetUserData( b2JointId jointId );
786:B2_API void b2Joint_WakeBodies( b2JointId jointId );
789:B2_API b2Vec2 b2Joint_GetConstraintForce( b2JointId jointId );
792:B2_API float b2Joint_GetConstraintTorque( b2JointId jointId );
795:B2_API float b2Joint_GetLinearSeparation( b2JointId jointId );
798:B2_API float b2Joint_GetAngularSeparation( b2JointId jointId );
804:B2_API void b2Joint_SetConstraintTuning( b2JointId jointId, float hertz, float dampingRatio );
807:B2_API void b2Joint_GetConstraintTuning( b2JointId jointId, float* hertz, float* dampingRatio );
810:B2_API void b2Joint_SetForceThreshold( b2JointId jointId, float threshold );
813:B2_API float b2Joint_GetForceThreshold( b2JointId jointId );
816:B2_API void b2Joint_SetTorqueThreshold( b2JointId jointId, float threshold );
819:B2_API float b2Joint_GetTorqueThreshold( b2JointId jointId );
829:B2_API b2JointId b2CreateDistanceJoint( b2WorldId worldId, const b2DistanceJointDef* def );
834:B2_API void b2DistanceJoint_SetLength( b2JointId jointId, float length );
840:B2_API void b2DistanceJoint_EnableSpring( b2JointId jointId, bool enableSpring );
846:B2_API void b2DistanceJoint_SetSpringForceRange( b2JointId jointId, float lowerForce, float upperForce );
852:B2_API void b2DistanceJoint_SetSpringHertz( b2JointId jointId, float hertz );
... [6 more lines]

Grep (typedef struct b2DistanceJointDef)

603:typedef struct b2DistanceJointDef
604-{
605-    /// Base joint definition
606-    b2JointDef base;
607-
608-    /// The rest length of this joint. Clamped to a stable minimum value.
609-    float length;
610-
611-    /// Enable the distance constraint to behave like a spring. If false
612-    /// then the distance joint will be rigid, overriding the limit and motor.
613-    bool enableSpring;
614-
615-    /// The lower spring force controls how much tension it can sustain
616-    float lowerSpringForce;
617-
618-    /// The upper spring force controls how much compression it an sustain
619-    float upperSpringForce;
620-
621-    /// The spring linear stiffness Hertz, cycles per second
622-    float hertz;
623-
624-    /// The spring linear damping ratio, non-dimensional
625-    float dampingRatio;
626-
627-    /// Enable/disable the joint limit
628-    bool enableLimit;
629-
630-    /// Minimum length for limit. Clamped to a stable minimum value.
631-    float minLength;
632-
... [31 more lines]

Read (E:\a327ex\Anchor2\engine\src\anchor.c)

6138     }
6139    
6140        // Create body definition
6141        b2BodyDef body_def = b2DefaultBodyDef();
6142        body_def.type = body_type;
6143        body_def.position = (b2Vec2){x / pixels_per_meter, y / pixels_per_meter};
6144    
6145        // Create body
6146        b2BodyId body_id = b2CreateBody(physics_world, &body_def);
6147    
6148        // Return body ID as userdata
6149        b2BodyId* ud = (b2BodyId*)lua_newuserdata(L, sizeof(b2BodyId));
6150        *ud = body_id;
6151    
6152        return 1;
6153    }
6154    
6155    static int l_physics_destroy_body(lua_State* L) {
6156        b2BodyId* body_id = (b2BodyId*)lua_touserdata(L, 1);
6157        if (!body_id) {
6158            return luaL_error(L, "Invalid body");
6159        }
6160    
6161        if (b2Body_IsValid(*body_id)) {
6162            b2DestroyBody(*body_id);
6163        }
6164        return 0;
6165    }
6166    
6167    static int l_physics_get_position(lua_State* L) {
... [22 more lines]

Everything I need is confirmed: distance joint is fully available (b2CreateDistanceJoint + spring/limit setters), and the binding pattern is clear — a body is a Lua userdata wrapping a b2BodyId, so a joint will be a userdata wrapping a b2JointId, created from two colliders' .body handles. One more detail — the v3.1 b2JointDef base uses local frames (transforms), not the old local anchors, so let me grab that struct to get the C right.

Grep (typedef struct b2JointDef)

562:typedef struct b2JointDef
563-{
564-    /// User data pointer
565-    void* userData;
566-
567-    /// The first attached body
568-    b2BodyId bodyIdA;
569-
570-    /// The second attached body
571-    b2BodyId bodyIdB;
572-
573-    /// The first local joint frame
574-    b2Transform localFrameA;
575-
576-    /// The second local joint frame
577-    b2Transform localFrameB;
578-
579-    /// Force threshold for joint events
580-    float forceThreshold;
581-
582-    /// Torque threshold for joint events
583-    float torqueThreshold;
584-
585-    /// Constraint hertz (advanced feature)
586-    float constraintHertz;
587-
588-    /// Constraint damping ratio (advanced feature)
589-    float constraintDampingRatio;
590-
591-    /// Debug draw scale
... [23 more lines]

I have the full picture now. Box2D v3.1 confirmed, distance joint fully available, and the binding shape is clear. Here's the step-1 brief — engine + framework joint bindings only (the capability); wiring the actual chain is the step after.

⛔ DESIGN BRIEF — Step 2a: Box2D distance-joint bindings in the engine

Goal: expose Box2D v3 distance joints to Lua, with enough surface to build and live-tune a springy chain. No gameplay change yet — this step ends when the engine compiles, the Lua wrappers load, and (optionally) a 2-body smoke test springs correctly.

How it maps onto the existing engine. A body is already a Lua userdata wrapping a b2BodyId (l_physics_create_body → lua_newuserdata(sizeof(b2BodyId))). A joint follows the identical pattern: a userdata wrapping a b2JointId, created from two colliders' .body handles, validity-checked with b2Joint_IsValid the way body funcs use b2Body_IsValid. All positions/lengths convert px↔meters via the existing pixels_per_meter global (bodies already do this at creation).

New C functions in anchor.c (registered next to the other physics_* via lua_register):

That set covers create / destroy / validity + live-tuning the spring stiffness, rest length, and limits — everything the chain needs.

New framework module anchor/joint.lua (procedural, like the other framework modules; collider stays the class). Thin ergonomic wrappers that take colliders and reach their .body:

Build / propagate flow. Edit Anchor2/engine/src/anchor.c (the one engine source) → cd Anchor2/engine && ./build.bat to verify it compiles → copy the rebuilt anchor.exe into mini-looper/. Add joint.lua to Anchor2/framework/anchor/ (source of truth) and copy into mini-looper/anchor/, wiring its require. I'll build to confirm compilation; I won't run it (you do).

Verification for this step: engine compiles clean, loadfile passes on the framework + game. Since nothing creates a joint yet, there's nothing to see — so if you'd like a visual confirmation before we commit to the chain rewrite, I can add a throwaway smoke test (distance-joint two of the current units and watch one spring off the other), then remove it. Otherwise we go straight to step 2b.

What's deliberately NOT in this step (it's step 2b): the chain assembly itself — making the head kinematic (so it tows the chain and is authoritative, switching to dynamic only during its own push), connecting consecutive units with these joints, removing the slot-follow follower code, and retuning (the SPACING/GAIN sliders become joint length + spring hertz/damping). I flag the head-kinematic decision now only so the direction is visible; I won't touch it yet.

Want me to proceed with 2a as scoped — and do you want the throwaway smoke test included, or straight bindings?

Go ahead.

Approved. I'll go with straight bindings (no throwaway smoke test — we'll see joints live in step 2b). First, three exact details before writing C: what b2DefaultDistanceJointDef initializes (esp. the local frames), the pixels_per_meter global, and the identity transform construction.

Grep (b2DefaultDistanceJointDef)

No matches found

Grep (pixels_per_meter\s=|float pixels_per_meter|static.pixels_per_meter|double pixels_per_meter)

507:static float pixels_per_meter = 64.0f;  // Default: 64 pixels = 1 meter
6002:    pixels_per_meter = scale;

Grep (b2Transform_identity|^} b2Transform|^} b2Rot|B2_API b2Transform b2MakeRot)

41:} b2Rot;
48:} b2Transform;
83:static const b2Transform b2Transform_identity = { { 0.0f, 0.0f }, { 1.0f, 0.0f } };

All confirmed: pixels_per_meter is a static global (64 default), b2Transform_identity exists in math_functions.h, and I'll call b2DefaultDistanceJointDef() then override fields (it sets the required internalValue). Let me check how the framework wires its module requires before I add joint.lua.

Read (E:\a327ex\mini-looper\anchor\init.lua)

1    --[[
2     Anchor 2 — framework initialization.
3   
4     Loads all framework modules in dependency order, then returns a function
5     that takes config and initializes the engine + global state. The game's
6     main.lua is expected to define `update(dt)` and `draw()` as globals; the
7     C engine calls these directly each frame.
8   
9     Usage (from a game's main.lua):
10      require('anchor')({
11        width = 480,
12        height = 270,
13        title = "My Game",
14        scale = 3,
15        vsync = true,
16        filter = "rough",
17        -- render_uncapped = true,   -- opt out of the 60Hz render cap; let
18                                     -- vsync pace render. Use for non-pixel-
19                                     -- art games where the cap shows judder.
20      })
21  
22      function update(dt)
23        sync_engine_globals()          -- refresh time/frame/etc. mirrors
24        -- your game update (physics is stepped by the engine automatically
25        -- before update() is called; you just consume collision events here)
26        process_destroy_queue()        -- drain deferred destruction
27      end
28  
29      function draw()
30        -- ... your game draw
... [140 more lines]

There's already an anchor.physics module — joints belong there rather than a new file (no new require needed). Let me read it to match its style.

Read (E:\a327ex\mini-looper\anchor\physics.lua)

1    --[[
2     physics — entity-resolving wrappers for physics queries.
3   
4     The C engine's physics_query_* and physics_get_*_begin/end functions return
5     raw body handles with tag names. These framework helpers:
6       1. Resolve bodies to their owning entities via physics_get_user_data + entities
7       2. Normalize event ordering so `a` always corresponds to the first tag
8          argument in the query and `b` to the second
9   
10    The normalization matters because the engine's `tags_match` is order-
11    insensitive, so a query like `collision_entities_begin('player', 'enemy')`
12    could receive events where the collision was recorded as
13    `tag_a='enemy', tag_b='player'`. Without normalization, you'd get `ev.a`
14    being the enemy when you expected the player. These helpers check the
15    tag names and swap if needed so `ev.a` is always the first-tag entity.
16  
17    Usage:
18      for _, ev in ipairs(collision_entities_begin('player', 'enemy')) do
19        ev.a:hit(1)   -- always the player (first query tag)
20        -- ev.b        -- always the enemy (second query tag)
21      end
22  
23      for _, ev in ipairs(sensor_entities_begin('bullet', 'enemy')) do
24        ev.a:kill()   -- the bullet
25        ev.b:hit(1)   -- the enemy
26      end
27  ]]
28  
29  -- Internal: resolve a body handle to its owning entity via user_data.
30  local function body_to_entity(body)
... [241 more lines]

Approved, straight bindings it is. I'll do the full propagation: engine C → build → copy exe, plus a joint.lua framework module mirrored into both Anchor2/framework/anchor/ (source of truth) and mini-looper/anchor/.

Starting with the engine C functions, inserted right after l_physics_destroy_body:

Edit (E:\a327ex\Anchor2\engine\src\anchor.c)

The file E:\a327ex\Anchor2\engine\src\anchor.c has been updated successfully. (file state is current in your context — no need to Read it back)

Now register the new functions:

Edit (E:\a327ex\Anchor2\engine\src\anchor.c)

The file E:\a327ex\Anchor2\engine\src\anchor.c has been updated successfully. (file state is current in your context — no need to Read it back)

Now the joint.lua framework module (both copies) and a check of the source-of-truth init's require block:

Write (E:\a327ex\Anchor2\framework\anchor\joint.lua)

File created successfully at: E:\a327ex\Anchor2\framework\anchor\joint.lua (file state is current in your context — no need to Read it back)

Write (E:\a327ex\mini-looper\anchor\joint.lua)

File created successfully at: E:\a327ex\mini-looper\anchor\joint.lua (file state is current in your context — no need to Read it back)

Grep (require('anchor.collider')|require('anchor.physics')|require('anchor.memory'))

73:require('anchor.collider')
74:require('anchor.physics')
75:require('anchor.memory')

Both inits match. Adding the require in both (source of truth + game copy):

Edit (E:\a327ex\Anchor2\framework\anchor\init.lua)

<tool_use_error>File has not been read yet. Read it first before writing to it.</tool_use_error>

Edit (E:\a327ex\mini-looper\anchor\init.lua)

The file E:\a327ex\mini-looper\anchor\init.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Need to Read the source-of-truth init before editing it:

Read (E:\a327ex\Anchor2\framework\anchor\init.lua)

56   -- Load framework modules (order matters for module dependencies)
57  require('anchor.class')
58  require('anchor.math')
59  require('anchor.array')
60  require('anchor.color')
61  require('anchor.object')
62  require('anchor.helpers')
63  require('anchor.input')
64  require('anchor.timer')
65  require('anchor.spring')
66  require('anchor.animation')
67  require('anchor.font')
68  require('anchor.image')
69  require('anchor.spritesheet')
70  require('anchor.layer')
71  require('anchor.shake')
72  require('anchor.camera')
73  require('anchor.collider')
74  require('anchor.physics')
75  require('anchor.memory')
76  
77  -- Global resource tables. Game code populates these via the resource loaders.

Edit (E:\a327ex\Anchor2\framework\anchor\init.lua)

The file E:\a327ex\Anchor2\framework\anchor\init.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Source-of-truth and game copies are in sync. Now building the engine to verify the C compiles:

Bash (cd /e/a327ex/Anchor2/engine && ls build.bat && cat build.bat | head -40)

build.bat
@echo off
setlocal

cd /d "%~dp0"

:: Find and run vcvarsall.bat for Visual Studio
if exist "C:\Program Files\Microsoft Visual Studio\18\Community\VC\Auxiliary\Build\vcvarsall.bat" (
    call "C:\Program Files\Microsoft Visual Studio\18\Community\VC\Auxiliary\Build\vcvarsall.bat" x64 >nul 2>&1
) else if exist "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat" (
    call "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat" x64 >nul 2>&1
) else if exist "C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Auxiliary\Build\vcvarsall.bat" (
    call "C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Auxiliary\Build\vcvarsall.bat" x64 >nul 2>&1
) else if exist "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\vcvarsall.bat" (
    call "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\vcvarsall.bat" x64 >nul 2>&1
) else (
    echo ERROR: Could not find Visual Studio
    exit /b 1
)

if not exist build mkdir build

:: Build Lua library if it doesn't exist
if not exist lib\lua.lib (
    echo Building Lua library...
    if not exist build\lua_obj mkdir build\lua_obj
    cl.exe /nologo /O2 /W3 /c /I"include/lua" ^
        include/lua/lapi.c include/lua/lauxlib.c include/lua/lbaselib.c ^
        include/lua/lcode.c include/lua/lcorolib.c include/lua/lctype.c ^
        include/lua/ldblib.c include/lua/ldebug.c include/lua/ldo.c ^
... [11 more lines]

MSVC build via vcvarsall. Running it (first build compiles the Lua lib + Box2D too, so it may take a bit):

Bash (./build.bat 2>&1 | tail -50)

anchor.c
include/stb\stb_image_write.h(776): warning C4996: 'sprintf': This function or variable may be unsafe. Consider using sprintf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(290): warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(1095): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(1312): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(2759): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(2753): warning C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
src/anchor.c(3150): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3428): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3434): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3544): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3553): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3647): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(3649): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(4907): warning C4996: 'strdup': The POSIX name for this item is deprecated. Instead, use the ISO C and C++ conformant name: _strdup. See online help for details.
src/anchor.c(6026): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(7017): warning C4244: 'initializing': conversion from 'lua_Number' to 'float', possible loss of data
src/anchor.c(7018): warning C4244: 'initializing': conversion from 'lua_Number' to 'float', possible loss of data
src/anchor.c(8791): warning C4244: '=': conversion from 'lua_Integer' to 'int', possible loss of data
src/anchor.c(8792): warning C4244: '=': conversion from 'lua_Integer' to 'int', possible loss of data
src/anchor.c(8798): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(8912): warning C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10256): warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10260): warning C4996: 'strcat': This function or variable may be unsafe. Consider using strcat_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10265): warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10269): warning C4996: 'strcat': This function or variable may be unsafe. Consider using strcat_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10275): warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10279): warning C4996: 'strcat': This function or variable may be unsafe. Consider using strcat_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10285): warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
src/anchor.c(10289): warning C4996: 'strcat': This function or variable may be unsafe. Consider using strcat_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
... [8 more lines]

Build successful: build/anchor.exe — only the usual pre-existing CRT warnings, no errors from the joint code. Now copy the exe into mini-looper and syntax-check the Lua:

Bash (cp /e/a327ex/Anchor2/engine/build/anchor.exe /e/a327ex/mini-looper/anchor.exe &&...)

exe copied (4192256 bytes)
ok   anchor/joint.lua
ok   anchor/init.lua
ok   loop.lua
ok   train.lua
ok   main.lua

Exe in place, all Lua loads. Let me do an engine boot sanity check — a headless one-frame verify (the Anchor2 engine-dev check; exits immediately, no window/playtest):

Bash (cat run.bat && echo "=== headless verify ===" && timeout 30 ./anchor.exe . --hea...)

@echo off
REM Run this game by its OWN folder name, so the template works after being
REM copied/renamed: fork snkrx-template into e.g. my-game and run.bat just
REM works without editing it. The engine resolves the game folder name
REM relative to CWD (= the parent directory).

cd /d "%~dp0.."
for %%I in ("%~dp0.") do set "GAME=%%~nxI"
"%~dp0anchor.exe" "%GAME%"
=== headless verify ===
Anchor Engine starting...
Headless mode enabled
Game folder: .
Loading: main.lua
Headless mode: skipping window and graphics initialization
Engine initialized (headless): 480x270
exit: 139

Step 2a is done. Here's the state:

One caveat to be honest about: I ran a headless one-frame verify as a boot check, and it segfaults (exit 139) — but after "Engine initialized (headless)" prints, i.e. during the game's draw, which is the graphics-heavy template (shaders/UI/layers) not surviving headless's skipped GL context. That's pre-existing to this template, not the joint bindings: my additions are registered during engine init (which completed fine) and aren't called anywhere yet. The engine getting through init confirms the registrations are valid.

So the real confirmation is a normal windowed run — which is yours. Since nothing creates a joint yet, it should look exactly like before (5 units, slot-follow, the same tuning panel on F1). If it boots and behaves identically, the new engine is good and we're clear for 2b.

What 2b will do (the chain itself, separate brief when you're ready): head goes kinematic as the chain's lead anchor, consecutive units get connected with joint_distance (springy — hertz/damping), the slot-follow follower code comes out, and the SPACING/GAIN sliders get repurposed to joint length + spring hertz/damping so you can tune the chain feel live.

Give it a windowed run to confirm the new engine boots clean, and tell me when to write the 2b brief.

Go ahead.

Here's the step-2b brief — the chain itself, all game-side (the engine bindings from 2a are done).

⛔ DESIGN BRIEF — Step 2b: the joint chain

Goal: replace slot-follow with a real distance-joint chain. The head leads exactly as it does now; followers become pure physics bodies towed by springy joints; a push on any unit propagates through the joints to both neighbors.

Roles / bodies:

Joints (in train_build): after spawning the pre-strung units, create joints for i = 2..n: unit.joint = joint_distance(units[i-1], units[i], { length = train_spacing, hertz = train_chain_hertz, damping_ratio = train_chain_damp }). Head has no joint. collide_connected stays false (jointed neighbors don't shove each other).

train_unit:update(dt, leader):

train_unit:destroy: joint_destroy(self.joint) before destroying the collider.

Live tuning (repurposed panel): SPACING → joint length; GAIN is replaced by HERTZ (spring stiffness) + DAMP (damping ratio). Each frame, push these to every joint (joint_set_length + joint_set_spring). The head knobs (SPEED / SEEK / EASE / CORNER / PUSH) stay. The panel reflows to fit the extra slider inside 270px — I'll compress the row heights (implementation detail, not a design change).

Globals: keep train_spacing (now = joint rest length); add train_chain_hertz (~4) and train_chain_damp (~0.7); remove train_follow_gain / train_follow_max.

The one risk + fallback: the head is dynamic and we set its velocity each frame, but the joint also pulls back on it during the solver step. With soft springs that drag is small, and the head re-asserts its velocity every frame, so it should lead cleanly while staying pushable. If the chain visibly drags the head (slows it, or yanks it off the loop on sharp corners), the fix is to make the head kinematic — perfect zero-drag towing — at the cost of the head no longer being pushable (we'd drop or special-case head-push). I recommend starting dynamic (keeps head pushable, minimal change) and switching only if drag shows up.

Expect to re-find good defaults for spacing/hertz/damp the way we did for the slot model — that's normal. Want me to build it?

Yea, sure, let's try this simple version of it first. My initial idea was more complicated than this but we can try that if this one doesn't work.

Building it. All game-side (train.lua + main.lua); no engine rebuild needed. Editing train.lua first — docblock, globals, the joint field, the head/follower split, joint creation, live-tuning, and joint cleanup:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the head/follower split in :update, the joint creation in train_build, the live-tuning + cleanup:

Edit (E:\a327ex\mini-looper\train.lua)

<tool_use_error>String to replace not found in file.
String:   if not self.pushed then
    if not leader then
      -- HEAD: walk the waypoint loop. Advance to the next point (wrapping)
      -- once we're within seek_distance of the current one.
      local tp = loop_points[self.path_index]
      if math.distance(self.x, self.y, tp.x, tp.y) < train_seek_distance then
        self.path_index = self.path_index%#loop_points + 1
        tp = loop_points[self.path_index]
      end

      -- Ease the HEADING (direction only) toward the waypoint; speed is kept
      -- separate below, so the smoothing knobs round the path without making
      -- the velocity magnitude sag.
      local target_r = math.angle_to_point(self.x, self.y, tp.x, tp.y)
      self.move_r = math.lerp_angle_dt(train_turn_p, train_turn_t, dt, self.move_r, target_r)

      -- Corner slowdown: scale speed by how far the heading still is from the
      -- target — straights run full speed, sharp turns ease off. Floor at 0.1
      -- so it never stalls. Shortest signed gap via math.loop (a plain angle
      -- calc, not a dt-lerp, so by-hand is fine).
      local gap = math.loop(target_r - self.move_r, 2*math.pi)
      if gap > math.pi then gap = gap - 2*math.pi end
      local factor = math.clamp(1 - train_corner_slow*(math.abs(gap)/math.pi), 0.1, 1)
      local speed  = train_max_speed*factor
      self.collider:set_velocity(speed*math.cos(self.move_r), speed*math.sin(self.move_r))
    else
      -- FOLLOWER: chase a slot train_spacing behind the leader, along the
      -- leader's heading (so the slot sits on the road — followers hug the
      -- path instead of chord-cutting toward the leader).
... [21 more lines]

Let me re-read the current :update to copy the exact text (likely an em-dash/whitespace mismatch):

Grep (if not self.pushed then)

98:  if not self.pushed then
99-    if not leader then
100-      -- HEAD: walk the waypoint loop. Advance to the next point (wrapping)
101-      -- once we're within seek_distance of the current one.
102-      local tp = loop_points[self.path_index]
103-      if math.distance(self.x, self.y, tp.x, tp.y) < train_seek_distance then
104-        self.path_index = self.path_index%#loop_points + 1
105-        tp = loop_points[self.path_index]
106-      end
107-
108-      -- Ease the HEADING (direction only) toward the waypoint; speed is kept
109-      -- separate below, so the smoothing knobs round the path without making
110-      -- the velocity magnitude sag.
111-      local target_r = math.angle_to_point(self.x, self.y, tp.x, tp.y)
112-      self.move_r = math.lerp_angle_dt(train_turn_p, train_turn_t, dt, self.move_r, target_r)
113-
114-      -- Corner slowdown: scale speed by how far the heading still is from the
115-      -- target — straights run full speed, sharp turns ease off. Floor at 0.1
116-      -- so it never stalls. Shortest signed gap via math.loop (a plain angle
117-      -- calc, not a dt-lerp, so by-hand is fine).
118-      local gap = math.loop(target_r - self.move_r, 2*math.pi)
119-      if gap > math.pi then gap = gap - 2*math.pi end
120-      local factor = math.clamp(1 - train_corner_slow*(math.abs(gap)/math.pi), 0.1, 1)
121-      local speed  = train_max_speed*factor
122-      self.collider:set_velocity(speed*math.cos(self.move_r), speed*math.sin(self.move_r))
123-    else
124-      -- FOLLOWER: chase a slot train_spacing behind the leader, along the
125-      -- leader's heading (so the slot sits on the road — followers hug the
126-      -- path instead of chord-cutting toward the leader).
127-      local slot_x = leader.x - train_spacing*math.cos(leader.move_r)
... [23 more lines]

The mismatch was if d > 0.5 (I'd written 0.001). Now I have the exact text. Splitting into two precise edits — add the head's facing line, then replace the follower block:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now joint creation in train_build, the live-tuning function + train_update, and joint cleanup in :destroy:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the main.lua tuning panel — replace SPACING/GAIN with SPACING/HERTZ/DAMP (9 sliders) and compress row heights to fit:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua
=== leftover refs to removed globals? ===
none (good)

Step 2b is in and clean — and since this is the first code that actually creates a joint, running it also confirms the 2a engine bindings end-to-end.

What changed (all game-side, no rebuild):

Test it:

The flagged risk to watch specifically: the head is dynamic, so the joint to unit 2 pulls back on it during the solve. With the soft default spring it should lead cleanly, but watch whether the head drags/slows or gets yanked off the loop on sharp corners. If it does, that's the signal to make the head kinematic (zero-drag tow, at the cost of head-push) — tell me and I'll switch it.

If the simple version reads well, we lock defaults; if it doesn't, you mentioned your original idea was more involved — we can go there next.

ERROR: anchor/joint.lua:25: Invalid body for distance joint stack traceback: [C]: in function 'physics_create_distance_joint' anchor/joint.lua:25: in function 'joint_distance' train.lua:170: in function 'train_build' main.lua:144: in main chunk

The body handle lives on the collider (collider.body), but train_build passes the train_unit entities (which have .collider, not .body) — so a.body is nil → "Invalid body." Let me confirm the collider's field name, then fix the call.

Grep (self.body\s*=|.body\b)

40:  self.body = physics_create_body(body_type, 0, 0)
44:    physics_set_user_data(self.body, owner.id)
51:    self.chain = physics_add_chain(self.body, tag, shape_args[1], shape_args[2] or true)
58:      self.shape = physics_add_circle(self.body, tag, shape_args[1], opts)
60:      self.shape = physics_add_box(self.body, tag, shape_args[1], shape_args[2], opts)
62:      self.shape = physics_add_capsule(self.body, tag, shape_args[1], shape_args[2], opts)
64:      self.shape = physics_add_polygon(self.body, tag, shape_args[1], opts)
74:  if self.body then
75:    physics_destroy_body(self.body)
76:    self.body = nil
86:  if self.owner and self.body then
87:    self.owner.x, self.owner.y = physics_get_position(self.body)

[Showing results with pagination = limit: 12]

Confirmed — collider.body is correct, so joint_distance wants colliders. The bug is train_build handing it the entities. Fixing the call to pass .collider:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   train.lua
ok   main.lua

Fixed — train_build now passes the colliders (train_units[i].collider) to joint_distance, which is what it expects (it reaches .body on them). The joint.lua contract was right; I'd just handed it the wrong objects.

Re-run it. You should now get the actual chain: head leading, 4 followers towed by springy distance joints. Same things to look at as before — does it read as a proper train, does SPACE propagate the kink both ways, and watch for any head-drag (the kinematic-head fallback if so). Tune SPACING / HERTZ / DAMP on F1.

Increase the number of units in the train to 12.

Trivial change — train_build(5) → train_build(12) in main.lua:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Done — the train now spawns 12 units. They start pre-strung behind the head along the initial heading, so the longer chain still forms cleanly. Run it and see how the longer conga reads — a longer chain will show any head-drag or corner-cutting more clearly, so it's a good stress test for the spring tuning (SPACING / HERTZ / DAMP on F1).

Self collisions (between train units) should be true. Default values: hertz = 10, damp = doesn't matter 0 or 2 doesn't seem to make a difference, spacing = 12. The problem with this approach is as I predicted, it works for pushing, but for following it means the units at the back don't actually follow the path of the follower, they just sort of hang around as it makes turns, which is what you would expect out of a physical chain. We want what I mentioned earlier, where default behavior is direct following, but with the chain still on, such that when units are perturbed, the chain behavior becomes predominant and thus things propagate backwards and forwards normally, but then it goes back to more strict following. This level of following vs. normal chain behavior can be a knob that I can change, but that also automatically changes itself when pushes happen.

Two parts here: the quick settings you gave (do now), and the model change (your original hybrid idea — that needs a brief before I code it).

First the quick ones — enabling train self-collision and setting the new defaults:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   train.lua
ok   main.lua

Settings applied and clean: train self-collision on (jointed neighbors skip it via collide_connected=false, so only non-adjacent units block each other), and defaults now spacing 12, hertz 10, damp 1.0. You can re-test the pure-chain model with those while reviewing this.

And your diagnosis is exactly the prediction — a physical chain follows like a chain (back units hang/cut on turns). Here's the brief for the hybrid you described.

⛔ DESIGN BRIEF — Step 2c: the follow ⇄ chain blend

Goal: default = followers trace the head's path directly (clean train); the joint chain stays on but only takes over when units are perturbed — so pushes still propagate both ways, then the train re-tightens to strict following. A FOLLOW knob sets the baseline; it auto-drops on a push and recovers.

Two components per follower:

  1. Follow (direct): a target on the head's actual path, i × spacing behind the head, driven by velocity toward it. Because every unit reads the head's path (not its neighbor's filtered motion), there's no compounding smear — it traces cleanly, SNKRX-style.
  2. Chain (physics): the existing distance joints + self-collision. They carry propagation when units are loose.

The blend (per unit, w ∈ [0,1]): velocity = lerp(physics_velocity, follow_velocity, w). w=1 → pure follow (joints overridden → crisp train); w=0 → pure physics (chain). w = FOLLOW × (1 − loose). The follow target is tracked tightly (effectively position-tracking via velocity, capped so re-tightening after a push is firm, not a teleport).

loose (per unit — the automatic shift): 0 normally. :push sets the pushed unit's loose = 1. Each frame it decays toward 0 and spreads to immediate neighbors, so a push opens a propagating band of loose units. Net: push → w→0 across a band → joints take over there → kink propagates front + back → loose decays → band re-tightens to strict follow. Exactly "chain becomes predominant on perturbation, then back to following," fully automatic — with FOLLOW as the manual baseline on top.

New machinery (all train.lua):

Sliders: add FOLLOW (0..1, default ~0.9). Looseness recovery-rate + spread start as constants; I'll promote them to sliders only if you want to tune the propagation feel (panel fits 10).

Honest caveats: at w=1 we override velocity each frame on bodies that also carry stiff (hertz 10) joints — the solver still nudges within a step. Strict follow should read clean, but if it jitters we soften the joints (they only matter during the loose phase) — a tuning step. And the loose recovery/spread rates are feel params we'll dial in.

Want me to build it?

Go ahead.

Building the hybrid. Let me do train.lua in two batches. First: the trail buffer global, the new knobs, the loose/index fields, push setting loose, and per-unit index at build:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Batch B: the follower blend branch, the trail/spread functions, and the train_update wiring (trail record → update → loose decay+spread):

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the main.lua panel — add the FOLLOW slider (10 total) and grow the panel:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Updating the train.lua docblock to match (title, followers paragraph, knob list):

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

All clean — the hybrid (step 2c) is in.

What it does now:

Test it:

The caveat I flagged, now concrete: the joints are at HERTZ 10 (stiff, from the pure-chain tuning), and on curves a stiff joint fights the follow (the joint wants straight-line spacing; the trail puts units slightly closer through bends). If you see jitter or spacing-fighting on curves, drag HERTZ down — in the hybrid the joints only need to be firm enough to propagate a push, the follow handles spacing. That's the first knob to reach for if it looks off.

If the propagation band feels too narrow/wide or too brief/long, that's train_loose_spread / train_loose_recover (constants right now) — say the word and I'll put them on sliders.

Hmmm, units are still not following properly, I think the physics overwrites everything, which makes sense. Let's try just the SNKRX snake style directly, no physics chain for now, just so I can see that it works and looks good.

Right — with the joints + self-collision on, the solver overrides our follow velocity, so the blend never reads as clean following. Let's strip the physics for the train and do pure SNKRX trail-follow: each follower pinned directly to the head's breadcrumb trail. Three edits.

Follower branch → pin to the trail (no physics):

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. The train is now a pure SNKRX snake: each follower is pinned directly to the head's breadcrumb trail, (index-1)×spacing back, set every frame — no joints, no self-collision, no physics fighting it. So it should trace the head's exact path cleanly.

What's live vs inert now:

Test it: it should finally read as a proper train hugging the loop — back units following the path, not swinging wide. That's the thing to confirm: does the SNKRX follow look good?

On pushing (SPACE) in this mode: since followers are rigidly pinned to the trail, pushing a follower does nothing (it snaps back). But pushing the head knocks it off the loop, and because the body follows the head's recorded trail, the whole snake follows the head's detour and back — that's the classic SNKRX behavior, and worth a look. (The thing we lose is mid-body perturbation/propagation — that's exactly what the physics chain was for, which we'll revisit once you've confirmed the clean follow looks right.)

If this looks good, we've got our baseline. The open question becomes how to reintroduce just enough physics for push-propagation without wrecking this clean follow — but let's see this first.

Following units are static and not following the head. Head continues moving normally.

Followers static while the head moves means the followers' trail target is coming back invalid (or d=0). Let me read the current train.lua to find which — most likely the per-unit index or the trail building.

Read (E:\a327ex\mini-looper\train.lua)

1    --[[
2     train.lua — the on-rails train (mini-looper, step 2c: follow + chain blend).
3   
4     The HEAD (unit 1, no leader) is a dynamic body driven kinematically: each
5     frame it eases a HEADING (self.move_r) toward the next waypoint and sets
6     its velocity at that heading (scaled by train_corner_slow in sharp turns).
7     It tows the rest of the train.
8   
9     FOLLOWERS (units 2..n) blend two behaviors. DIRECT FOLLOW drives each unit
10    toward the head's breadcrumb trail, (index-1)*spacing back, so every unit
11    traces the HEAD's actual path (no compounding smear). CHAIN is a springy
12    Box2D distance joint to the unit ahead (rest length train_spacing,
13    train_chain_hertz / train_chain_damp) + self-collision. The per-unit blend
14    is w = train_follow*(1 - loose): w=1 strict follow, w=0 pure chain. loose
15    is 0 normally; :push spikes it to 1, it spreads to neighbors and decays, so
16    a push hands a propagating band to the chain (kink travels both ways) then
17    re-tightens.
18  
19    `:push` (a verbatim port of seeker:push) applies a physics impulse + spin
20    to ANY unit; the joint network carries the kink to both neighbors (front
21    and back) and the springs settle it back. SPACE pushes a random unit via
22    train_push_random().
23  
24    Live-tunable feel knobs (the tuning UI in main.lua writes them):
25      train_max_speed, train_seek_distance, train_push_force,
26      train_turn_p / train_turn_t (head heading-ease), train_corner_slow
27      (head slow-in-turns), the chain trio train_spacing / train_chain_hertz /
28      train_chain_damp, and train_follow (follow vs chain baseline).
29      train_loose_recover / train_loose_spread / train_follow_speed_cap are
30      tuned constants.
... [269 more lines]

The code reads correctly, so the static followers point to one of two silent failures: either self.index is getting clobbered (making d = (index-1)*spacing = 0 → trail_point_at returns nil), or the trail isn't building. Let me check whether make_entity sets an index field that collides with mine.

Grep (function make_entity|.index\b|self.index)

mini-looper\anchor\array.lua:292:    array.index({2, 1, 2}, 2)                                          -- 1
mini-looper\anchor\array.lua:293:    array.index({2, 1}, 1)                                             -- 2
mini-looper\anchor\array.lua:294:    array.index({4, 4, 4, 2, 1}, function(v) return v % 2 == 1 end)   -- 5
mini-looper\anchor\array.lua:302:function array.index(t, v)
mini-looper\anchor\object.lua:74:function make_entity(e)

trail_point_at itself works (the hybrid was reading it), so static-on-set_position is suspicious. But to stop guessing, let me read main.lua's update wiring and make_entity to confirm train_update runs and nothing clobbers state.

Read (E:\a327ex\mini-looper\main.lua)

200        return lo + res.value*(hi - lo)
201     end
202     train_max_speed     = tuner('tune_speed',  'SPEED',   train_max_speed, 0, 500)
203     train_seek_distance = tuner('tune_seek',   'SEEK',    train_seek_distance, 2, 40)
204     train_push_force    = tuner('tune_push',   'PUSH',    train_push_force, 0, 30)
205     train_turn_p        = tuner('tune_turn_p', 'EASE P',  train_turn_p, 0.50, 1.00, '%.2f')
206     train_turn_t        = tuner('tune_turn_t', 'EASE T',  train_turn_t, 0.02, 0.50, '%.2f')
207     train_corner_slow   = tuner('tune_corner', 'CORNER',  train_corner_slow, 0.00, 1.00, '%.2f')
208     train_spacing       = tuner('tune_space',  'SPACING', train_spacing, 4, 40)
209     train_chain_hertz   = tuner('tune_hertz',  'HERTZ',   train_chain_hertz, 0.5, 20, '%.2f')
210     train_chain_damp    = tuner('tune_damp',   'DAMP',    train_chain_damp, 0.0, 2.0, '%.2f')
211     train_follow        = tuner('tune_follow', 'FOLLOW',  train_follow, 0.0, 1.0, '%.2f')
212   end
213 
214   --[[ ATTACKS — fire a carrier here.  Bind a key in the INPUT section
215        above, then call its spawn_* helper on the press. Every carrier's
216        list + update/draw loop is already wired below, so this is the
217        ONLY code a new attack needs. Full opts: snkrx/<carrier>.lua.
218 
219          spawn_projectile(p, { damage = 1, speed = 190, max_range = 220,
220            fire_sounds = {{ sound = sounds.arrow_shoot,
221                             vol   = volumes.arrow_shoot }} })
222 
223          spawn_area(main_camera.mouse.x, main_camera.mouse.y,
224            { radius = 30, damage = 2, caster = p, shape = 'circle' })
225            -- shape 'rect' / 'polygon'; pass duration = N for a DoT area
226 
227          spawn_beam(p, { damage = 2, length = 600 })
228            -- persistent = true to channel it (hold to fire, release to stop)
229 
... [15 more lines]

Read (E:\a327ex\mini-looper\anchor\object.lua)

74   function make_entity(e)
75    e.id = next_id
76    next_id = next_id + 1
77    entities[e.id] = e
78    if not e.kill then e.kill = default_kill end
79    return e
80  end
81  
82  --[[
83    entity_kill(e)
84    Free function equivalent to e:kill(). Useful if you have a plain
85    entity table and don't want to use method syntax.
86  ]]
87  function entity_kill(e)
88    default_kill(e)
89  end
90  
91  --[[
92    process_destroy_queue()
93    Called once at the end of every frame in the game's main update.
94    Drains the destroy queue until stable (entity destruction may cause
95    more kills via polling in other entities' destroy methods).

Found it. The bug is in train_trail_update — and it's been there since I wrote it (the joints masked it in the hybrid; pure-trail mode exposed it).

The logic was: "if the head moved ≥1.5px since the last trail point, add a point; else move that last point to the head." The problem: this engine steps physics faster than 60Hz, so the head moves less than 1.5px per step. That means every frame takes the else branch — which keeps resetting the single trail point onto the head — so the distance never accumulates, the trail never grows past one point, and trail_point_at always returns nil → followers get no target → static. (In the hybrid this was hidden because the joints were moving them anyway, which is exactly why it looked like "physics overwrites everything" — the follow was never actually engaging.)

Fix: drop the else so the distance accumulates across sub-step frames, and commit a point every 2px regardless of per-step speed.

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok train.lua

Fixed and clean. Now the trail actually builds, so the followers should track the head's path properly — the pure SNKRX snake you wanted.

Run it: you should see all 12 units trail the head along the loop, hugging the path (not the chain's corner-cutting). SPACING controls the gap.

Worth noting: this same bug is why the hybrid "didn't follow" earlier — the follow target was always nil, so the blend never engaged and you were only ever seeing the joints (hence "physics overwrites everything"). So once you've confirmed this clean follow looks good, the hybrid is actually more promising than it looked — the follow half was silently broken the whole time, not losing to physics. But let's get your eyes on the clean SNKRX follow first.

OK, go ahead and bring back the hybrid so I can see.

On it — restoring the hybrid (the follow side actually works now). Three reverts: the follower branch back to the velocity-blend, joint creation back in train_build, and train self-collision back on.

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Hybrid's back and clean — and this time the follow side actually engages.

What to look for now:

The caveat that now matters (since follow is live): the joints are at HERTZ 10 (stiff). On curves the stiff joint wants straight-line spacing while the follow pulls units to slightly-closer trail points — they can fight, showing as jitter or spacing tension on bends. If you see that, drag HERTZ down first; in the hybrid the joints only need to be firm enough to carry a push, the follow handles spacing. (DAMP and FOLLOW are the other dials; SPACING is the gap.)

If the follow looks clean at high FOLLOW and the push still propagates nicely, that's the behavior you described. If the curve-fight is bad even at low HERTZ, the fallback is to drive followers by position during follow (like the pure-trail mode) and only hand to the joints when loose — but try the velocity-blend version first.

Hertz = 2, damp = 0.5, follow = 0.33. The behavior seems correct now, except the way in which it goes back to normal after a push seems a bit incorrect. Also, the spread to nearby units doesn't seem to be that strong, the push is mostly singular on the unit that's pushed without affecting others that much (although it affects them some).

Good — the hybrid's working in principle. Let me set your defaults and address both issues. The propagation weakness has a clear cause: at HERTZ 2 the joints are too soft to tug neighbors even when they go loose. So I'll make the joints stiffen inside the loose band (soft while following → no curve-fight; stiff where a push is happening → strong propagation), and hold a unit fully loose while it's pushed so the band doesn't decay mid-push.

Edits to train.lua — defaults + the loose-stiffness boost + hold-loose-while-pushed:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now expose RECOVER (the loose decay rate, for tuning how it returns to normal) on the panel, compressing rows to fit 11 sliders:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

All clean. Here's what changed for your two issues:

Propagation strength (the weak spread): the root cause was HERTZ 2 — soft joints can't tug neighbors even once they go loose. Now the joints stiffen inside the loose band: each joint's hertz = HERTZ + loose × 18, so a unit in a pushed band gets joints up to ~20Hz (strong yank → real propagation to both sides), while the following chain stays at 2Hz (no curve-fight). So the spread should now actually move neighbors, not just flag them. (The band width is still train_loose_spread; the new strength comes from the stiffening. If it's still not enough, the train_chain_push_hertz = 18 constant is the dial — say so and I'll raise it or put it on a slider.)

Recovery: two changes — a unit now stays fully loose while it's being pushed (so the chain-mode band doesn't decay out from under the push mid-way), and I put RECOVER on the panel (the loose-decay rate: lower = lazier return to follow, higher = snappier). Defaults set to HERTZ 2 / DAMP 0.5 / FOLLOW 0.33, RECOVER 2.0.

Test the push now — propagation should read much stronger, and you can dial RECOVER to shape the return.

But I was guessing at "goes back to normal a bit incorrect" — can you pin it down so I target it precisely? Which is it:

Knowing which one tells me whether to reach for RECOVER, the follow re-engage cap, the damping, or the order of the loose decay.

Make it so that space can never push the head.

Trivial change — train_push_random now picks only from followers (index 2+), never the head:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok train.lua

Done. SPACE now only ever pushes a follower (units 2–12); the head is never pushed, so it keeps leading and laying the trail uninterrupted while you watch the chain react around the shoved unit.

Recover doesn't seem to practically do much, and the way the push spreads and happens seems incorrect. Let's not waste any more time on this. Give me a toggle that turns of physics behavior entirely and leaves me with just SNKRX direct follow, and the other toggle which makes it behave like now. I want to be able to see if the difference in movement is too big and which one I prefer. We'll scrap the notion of pushing train units entirely because it's not strictly necessary for gameplay. So I just want to see the difference in terms of movement behaviors.

Makes sense — let's stop tuning the physics and just give you a clean A/B. I'll add an M toggle that switches followers between pure SNKRX trail-follow (no physics) and the physics-chain blend, with an on-screen label so you know which you're in. The head is identical in both (drives the loop, lays the trail); only the followers' movement differs.

train.lua — the mode flag and the branched follower update:

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now main.lua — the M binding, the toggle, and the on-screen mode label:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Clean. You've got the A/B:

Flip back and forth on the same loop and see whether the physics blend's looseness/jostle is worth the cost over the dead-clean SNKRX follow, or if the clean version is just better for the game. Tell me which you land on and we'll lock it in (and rip out the unused path — if you pick SNKRX we can delete the joints/loose machinery entirely and simplify the whole file).

Does SNKRX mode actually kill the physics objects or are they still active?

[Request interrupted by user]

By physics objects I mean the chain.

Good question — and the honest answer is no, SNKRX mode does not currently kill the chain. The distance joints are still created at build and stay in the Box2D world; the solver still runs them every step, train_apply_chain_tuning still tunes them, and train↔train self-collision is still on. In SNKRX mode the followers' set_position just overrides the result each frame, so you don't see the joints move them — but they're live, and worse, a non-adjacent follower overlapping the head could still shove the head via self-collision (the head is dynamic). So it's not a clean baseline — which defeats the comparison.

Let me fix that so the toggle genuinely creates/destroys the chain. In SNKRX mode: joints destroyed, self-collision off — nothing physics touches the train.

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua

Fixed and clean. Now M genuinely makes/breaks the chain:

train_set_chain_active(active) does the create/destroy + collision enable/disable, called on every M press (and once at build to match the starting mode). So your A/B is now actually apples-to-apples — SNKRX is real SNKRX, no residual solver work or stray collisions contaminating it.

One thing to watch: I'm toggling physics_enable/disable_collision at runtime (not just at setup). It should take effect on new contacts immediately; if you ever see train units behaving oddly with collisions right after a toggle, tell me and I'll confirm the runtime toggle is clean. Otherwise, flip freely and judge the two movement feels side by side.

OK, let's go with SNKRX mode. Let's additionally add a small system such that when velocity is increased (base is 100) it also decreases T and increases corner. At 200 velocity T should be 0.15 (starts at 0.3) and corner should be 0.75 (starts at 0.4). You can remove the physics chain/joints entirely from the game, or leave it commented out, whatever you prefer.

SNKRX it is. I'll add the velocity→turn coupling and clean the physics chain out entirely (the joint.lua module + engine bindings stay available, just unused — easy to revive from git if ever needed). Rewriting train.lua to the clean SNKRX-only version:

Write (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the main.lua cleanup — remove the mode/push bindings, handlers, mode label, and slim the panel to SPEED/SEEK/SPACING with a read-only readout of the auto-derived EASE T / CORNER:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Now the panel and the (removed) mode label:

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\main.lua)

The file E:\a327ex\mini-looper\main.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok   loop.lua
ok   train.lua
ok   main.lua
=== dangling refs to removed chain/push symbols? ===
none (clean)

Clean, no dangling references. Done:

Velocity → turn coupling (train_apply_speed_coupling, runs each frame off train_max_speed):

Cleaned out the physics chain entirely (train.lua is now pure SNKRX): removed the joints, train_set_chain_active, self-collision, the loose/spread/recover machinery, the physics-mode follower branch, the M toggle + mode label, and the push system (per scrapping it). The joint.lua module and engine bindings stay in the tree, just unused — easy to revive from git if ever needed.

Panel (F1) is now just SPEED / SEEK / SPACING sliders, plus a read-only EASE T / CORNER readout so you can watch the coupling as you drag SPEED.

Test: drag SPEED and confirm EASE T drops + CORNER rises (readout updates), and that the train still hugs the loop cleanly at higher speeds rather than swinging wide. SEEK and SPACING behave as before. That should be the whole movement system locked in — a clean SNKRX snake whose turn response scales with speed.

If the coupling curve feels off at the extremes (very slow or very fast), the anchor points / clamps in train_apply_speed_coupling are a one-line tweak.

Perfect. There's another small issue which is that the distance between the head and the first tail unit is like 1 or 2 pixels higher than it should be. Do you have any idea why?

Yes — I know exactly why, and your 1-2px estimate matches the cause precisely.

The follower measures its distance back along the trail, but the trail's most-recent point (train_trail[1]) isn't the head — it's the last committed point, and I only commit a new one every ~2px of head travel. So between commits, train_trail[1] lags the actual head by up to 2px. Unit 2 sits 12px back from that lagging point, i.e. 12 + (lag up to 2) from the real head → the gap reads ~13-14px instead of 12. (Every unit inherits the same small offset, but it's most noticeable head→unit 2.)

Fix: anchor the measurement at the head's live position, then walk the committed trail — so the lag is absorbed into the first segment and the distance is exact.

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Edit (E:\a327ex\mini-looper\train.lua)

The file E:\a327ex\mini-looper\train.lua has been updated successfully. (file state is current in your context — no need to Read it back)

Bash (cd /e/a327ex/mini-looper && LUA=/e/a327ex/Anchor/reference/love-compare/tools/lu...)

ok train.lua

Clean. The follower spacing is now measured from the head's live position through the committed trail, so the head→unit 2 gap (and every gap) is exactly SPACING instead of SPACING + commit-lag. Run it — the head-to-first-unit distance should match the rest now, no more 1-2px bulge.

Great. Seems like everything is fixed and we finished movement entirely. Next session we'll handle enemies and attacks. You may end the session, name it Mini Looper 1. Create a private repo for it if it hasn't been created already.

I'll invoke the end-session workflow (it handles the transcript → summary, commit, and push). Let me start it with the session name.

Skill 

Launching skill: end-session

Base directory for this skill: E:\a327ex.claude\skills\end-session

End Session Workflow

This skill is invoked from the same conversation where the work was done. You already have the full session context in memory — you do NOT need to read the transcript.

Step 1: Get Session Info

Ask the user for the session title (max 30 characters). Examples: "Anchor Phase 10 Part 5", "Physics Arena Setup", "Timer System Fix", "Thalien Lune Design".

Determine the project yourself from your session context — you know which repo(s) were worked on, which files were created/modified, and where they live. No need to ask. See Step 5 for the list of known project roots; if the session touched something outside the list, infer the root from the paths you actually edited.

Step 2: Write Summary

Write the summary from your conversation memory. You have the full session context — no need to read any files.

The summary should be thorough and detailed. Each major topic deserves its own section with multiple specific bullet points. Don't compress — expand.

Purpose: These summaries serve as searchable records. Future Claude instances will grep through past logs to find how specific topics were handled. The more detail you include, the more useful the summary becomes for finding relevant context later.

Format (this is just an example structure — adapt sections to match what actually happened):

# [Title]

## Summary

[1-2 sentence overview of the session's main focus]

**[Topic 1 - e.g., "Spring Module Implementation"]:**
- First specific detail about what was done
- Second detail - include file names, function names
- User correction or feedback (quote if notable)
- Technical decisions and why

**[Topic 2 - e.g., "Camera Research"]:**
- What was researched
- Key findings
- How it influenced implementation

**[Topic 3 - e.g., "Errors and Fixes"]:**
- Specific error message encountered
- Root cause identified
- How it was fixed

[Continue for each major topic...]

---

[Rest of transcript follows]

Rules: - Be thorough — If in doubt, include more detail, not less. Each topic should be as detailed as possible while still being a summary. - Think searchability — Future instances will search these logs. Include keywords, function names, error messages that someone might grep for. - One section per major topic — Don't combine unrelated work into one section - Chronological order — Sections should match conversation flow - Specific details — Error messages, file names, function names, parameter values - Include user quotes — When user gave notable feedback, quote it (e.g., "k/d variables are not intuitive at all") - Weight planning equally — Research, proposals, alternatives considered, user feedback on approach are as important as implementation - Weight problems solved — Errors, root causes, fixes, user corrections all matter - Technical specifics — Include formulas, API signatures, parameter changes when relevant

Step 3: Proceed Without Approval

Do NOT show the summary to the user for approval. Write it directly. The user can review the committed log after the fact and request a follow-up edit if anything is off.

Step 4: Convert Transcript and Write the Log File

# Find recent sessions (Claude + Cursor + Codex). Same script lives in Anchor2:
python E:/a327ex/Anchor2/scripts/find-recent-session.py --limit 5
# or: python E:/a327ex/Anchor/scripts/find-recent-session.py --limit 5

The script shows sessions sorted by when they ended. The first result is the current conversation (since end-session was invoked here). Use it.

Use a lowercase hyphenated slug derived from the title (e.g., "anchor-primitives-hitstop-animation").

Get the end timestamp for the Date frontmatter — this is the wall-clock time when end-session was invoked, NOT the time the JSONL started. Sessions often span multiple days, and the log should be filed under the day the work was wrapped up:

date "+%Y-%m-%d %H:%M:%S"

Use this output verbatim. Do not substitute the JSONL start timestamp; the log appears in the sidebar sorted by Date, and a multi-day session with a Date pinned to day 1 will sort below sessions that ended later but started later, hiding the most recent work.

Convert the transcript to markdown:

python E:/a327ex/Anchor2/scripts/jsonl-to-markdown.py [SESSION_PATH] /tmp/session-log.md
# or: python E:/a327ex/Anchor/scripts/jsonl-to-markdown.py ...

The same script auto-detects Claude Code JSONL vs Cursor/Composer agent JSONL (~/.cursor/projects/.../agent-transcripts/...) vs Codex rollouts (~/.codex/sessions/...). For Composer sessions, use find-recent-session.py (it merges all sources) and pick the [cursor] line for the current chat.

Replace the default header (# Session YYYY-MM-DD...) at the top of /tmp/session-log.md with the approved title and summary, AND prepend frontmatter. The final file shape:

Title: [Title]
Date: YYYY-MM-DD HH:MM:SS

# [Title]

## Summary

[approved summary text from step 2]

---

[transcript content from jsonl-to-markdown script]

Frontmatter is non-negotiable. Every log file MUST start with Title: and Date: lines. Without them, the site's sidebar shows the slug as the title and 0 (epoch) as the sort date. The backfill script in a327ex-site/deploy/backfill_metadata.py is a safety net, not a substitute — write it correctly the first time.

Then copy the final file to the log destination:

cp /tmp/session-log.md E:/a327ex/a327ex-site/logs/[slug].md

Step 4.5: Decrement the lock (if active)

Read E:/a327ex/a327ex-site/.lock.json if it exists. If it contains {"remaining": N} with N > 0:

  • Decrement N by 1
  • Write {"remaining": N-1} back to the file
  • If N becomes 0, the lock is cleared. You may leave the file at {"remaining": 0} or delete it; both work.

The lock file lives in the a327ex-site repo, so the change is staged automatically by git add -A in Step 6.

If no lock file exists or remaining is already 0, do nothing. (See the /lock skill for the lock's full design.)

Step 5: Commit Project Repo

Identify the project repo(s) worked on this session from your own context — you already know which repos were touched and which files changed. For the common projects:

Project Root Stage command
Anchor E:/a327ex/Anchor git add docs/ framework/ engine/ scripts/ reference/
Anchor2 E:/a327ex/Anchor2 git add framework/ engine/ arena/ reference/ scripts/ docs/ .claude/
emoji-ball-battles E:/a327ex/emoji-ball-battles git add -A
invoker E:/a327ex/Invoker git add -A
thalien-lune E:/a327ex/thalien-lune git add -A
a327ex-site E:/a327ex/a327ex-site git add -A (this IS one of the web repos — the log file added in Step 4 is staged here automatically)

For a project not listed, infer the root from the files you actually created or modified this session and stage those. If multiple candidate roots look valid, ask the user which files to stage.

cd into the project root, stage, run git status to verify before committing.

IMPORTANT — FULL SUMMARY IN COMMIT: The commit message MUST include the FULL summary from the log file. Read the summary back from the log file to ensure nothing is missing.

IMPORTANT — COMMIT METHOD: The summary contains backticks, special characters, and markdown that WILL break heredocs and git commit -m. ALWAYS use the file-based method below. NEVER try a heredoc first — it will fail and produce a malformed commit that needs amending.

# Skip until we hit the line "## Summary", then take everything after the next
# blank line until the --- separator that precedes the transcript.
awk '/^## Summary$/{found=1; next} found && NR>1 && /^---$/{exit} found' \
    E:/a327ex/a327ex-site/logs/[slug].md > /tmp/commit_msg.txt

# Prepend the title (plain text, no #) and append attribution
sed -i "1i [Title]\n" /tmp/commit_msg.txt
printf "\nGenerated with [Claude Code](https://claude.com/claude-code)\n\nCo-Authored-By: Claude <noreply@anthropic.com>\n" >> /tmp/commit_msg.txt

git commit -F /tmp/commit_msg.txt

Step 6: Push the Repos

Two pushes — project (to GitHub) and a327ex-site (to the VPS):

# Project repo to GitHub. Skip this push if the project IS a327ex-site
# (handled by the second push below — don't duplicate).
git push origin main

# a327ex-site to the VPS (post-receive hook restarts the Lua server).
cd E:/a327ex/a327ex-site
git add -A
git commit -m "[Title]"
git push prod main 2>&1 | tail -3

Failure handling: if either push fails, the other still happens. Local commits stay intact, so the user can re-push manually once they've fixed whatever blocked it. Don't roll back; the committed state on disk is the source of truth.

Step 7: Confirm

Tell the user: - Project commit hash + GitHub push result - a327ex-site commit hash + VPS push result

Format:

Logged — "[Title]".
  project (Anchor2):  abc1234  pushed to GitHub
  a327ex-site:        ghi9012  pushed to a327ex.com (post-receive deployed)

If a push failed, surface that explicitly with the error.

Notes

  • Frontmatter is non-negotiable. Every log file MUST have Title: and Date: at the top. Enforced at write time in step 4. The backfill script is a safety net, not a substitute.
  • If the project IS a327ex-site (e.g., you spent the session writing the renderer or fixing the theme), there's no separate "project repo to GitHub" push — the a327ex-site push at the end IS the project push. Don't duplicate.
  • Legacy note: this skill used to also dual-write to anchor.blot.im/logs/ and anchor.blot.im/context/. Post-cutover (May 2026), anchor.blot.im is a JS redirect to a327ex.com and no longer receives content. Drop those steps if you find any older docs that still reference them.

ARGUMENTS: Mini Looper 1

The title's set ("Mini Looper 1", 13 chars — fits). This session touched two repos — the new mini-looper game and the Anchor2 engine/framework (the Box2D joint bindings). Let me gather state before writing the log.

Bash (echo "=== mini-looper repo (verify private exists) ===" && gh repo view a327ex/m...)

=== mini-looper repo (verify private exists) ===
{"name":"mini-looper","sshUrl":"git@github.com:a327ex/mini-looper.git","visibility":"PRIVATE"}

=== mini-looper git status ===
 M anchor.exe
 M anchor/init.lua
 M main.lua
?? anchor/joint.lua
?? loop.lua
?? train.lua

=== Anchor2 is a git repo? + status ===
E:/a327ex/Anchor2
 D app/actions.lua
 D app/anchor/animation.lua
 D app/anchor/array.lua
 D app/anchor/camera.lua
 D app/anchor/class.lua
 D app/anchor/collider.lua
 D app/anchor/color.lua
 D app/anchor/font.lua
 D app/anchor/helpers.lua
 D app/anchor/image.lua
 D app/anchor/init.lua
 D app/anchor/input.lua
 D app/anchor/layer.lua
 D app/anchor/math.lua
 D app/anchor/object.lua
 D app/anchor/physics.lua
 D app/anchor/shake.lua
... [23 more lines]

Repo's confirmed (private, exists), session JSONL located, lock at 10 (will decrement to 9). Note Anchor2 has unrelated pre-existing app/ deletions — I'll stage only my engine/framework files. Let me convert the transcript and see exactly which Anchor2 files are mine to stage.