Painted animation

A method for making short cartoons entirely in code, distilled from JohnHeibel/PDoomVideo (a 156 s music video painted by Claude Opus) and its generalised kit ClaudeAnimationBase (MIT), which is bundled here as template/.

How it works: every frame is a pure function of time t. studio.html loads p5.js + p5.brush and your scene files; each shot paints the whole 1920×1080 frame with watercolour fills and boiling ink lines. render.mjs drives headless Chrome to render contact sheets for review, or every frame in parallel, and ffmpeg encodes the MP4 (with audio if given).

Workflow

0. Scaffold

bash ~/.claude/skills/painted-animation/scripts/new_project.sh <project-dir>        # add --keep-demo to keep the example scene hooked up

This copies the template, unhooks the demo scene, runs npm install and checks node / ffmpeg / Chrome. Then read <project-dir>/ANIMATION_GUIDE.md in full before designing anything: it holds the rules, the animation principles and the complete engine / Clawd API. Look at docs/emotions.jpg and docs/views.jpg (the model sheets) with the Read tool.

For a music video or anything longer than ~20 s, also read references/music-video.md. For a lyric video, ask for the song file and an LRC first, and measure the tempo with scripts/beat_grid.py: lines are usually faster than you'd guess.

1. Storyboard before code

Write STORYBOARD.md in the project (format in the guide: logline, world + palette arc, motif, the character's emotion arc, then shots with reads — the timed list of what the viewer must understand). Worked example: examples/xiaozhen/ (a 31 s lyric video: storyboard and full scene code).

Show the storyboard to the user and let them react before building, unless they said to just go ahead.

2. Build shot by shot

• Set duration, bpm, offset (and audio) in src/config.js.
• One IIFE-wrapped file per scene/chapter in src/scenes/, ending with shots([[t0, fn], ...]); add its <script> to studio.html.
• Block key poses first, check them as stills, then add the motion between them.

3. Render and look — every shot, several times

You can't see motion by reading code. From the project dir:

node render.mjs --sheet=0.1,0.8,1.6,2.4 --cols=4 --w=480 --out=out/check/a.jpg        # key frames
node render.mjs --strip=2.1:2.6 --out=out/check/strip.jpg                             # every frame of a moment
node render.mjs --sheet=2.3 --crop=760,420,500,400 --w=500 --out=out/check/face.jpg   # full-res detail

Open each image with Read and actually check it against the guide's review list: event clear? character big enough? reads timed so a first-time viewer gets them? anticipation / follow-through, no snaps? feet and held props touching? transitions at every seam? no text, no 3D, no pure black/white, no muddy glows? Fix and look again. Budget: ≥ 1 sheet per shot, a strip per key motion and transition, a crop per story-carrying face.

4. Render the video

node render.mjs --clip --out=out/video.mp4                                   # short videos, one worker
node render.mjs --frames --workers=4 && node render.mjs --encode --out=out/video.mp4 [--audio=assets/song.mp3]   # long ones, parallel + resumable

Report the output path, length and ms/frame. Offer open out/video.mp4.

The rules that matter most

These are the guide's rules condensed; the guide is authoritative.

1. Handmade medium. Only paint() / inkLine() (p5.brush) — never plain p5 rect/ellipse/fill. Flat 2D only: turns go through drawn key views (turn(), spinView()), never 3D projection. Light via glow() (additive), because pigment-mixing makes yellow-over-blue go green.
2. No text. No captions, labels, signs or word bubbles; show it instead. Reactions are painted emotes (!, sweat, hearts…). The one exception is karaoke in a lyric video, and at most a few big SFX.
3. Something happens in every shot — an event, cause → reaction, set-ups that pay off.
4. Time for the viewer. List each shot's reads; one read at a time; fast actions, held meanings; lead the eye; the reads set the shot length. This is where generated animation fails most.
5. Alive. Nothing is still (idles from feel(), drifting cameras, boil); faces change through emotions() never by swapping; the character is big (medium shot u≈20–28, close-up 40–70); everything rides the beat.
6. Transitions at every seam, chosen to fit the story (brush wipe, iris / shaped iris, whip pan, match cut, cut on action, camera carry-through).
7. One piece. One world, a colour arc, an emotional thread, linked scenes, an ending that rhymes with the opening.

Engine gotchas

• Pure functions of t. Frames render in parallel and out of order: no state across frames, no Math.random(), no frame-by-frame physics. hash(i) for stable randomness, jit() for boil.
• boilSeed(key) before each separate background element/prop, or a moving thing makes everything drawn after it re-boil every frame (jitter).
• Don't name globals after p5's. p5 defines line, OVERLAY, text, color, scale, … as globals; a top-level function line() fails with Cannot redefine property and the page never becomes ready (the renderer times out). Keep helpers inside the scene IIFE or give them distinct names.
• Layering in doorways, windows and screens: draw what's inside, then paint the surrounding wall/frame back over it, so nothing wider than the opening shows outside it (the train's inDoor + door jambs, the TV bezel pieces).
• A NaN in a point list throws Failed to construct 'OffscreenCanvas' — guard degenerate geometry.
• Under camera zoom ≳ 2, huge shapes lose outlines; outline weight scales with zoom, so scale sw down in close-ups.
• Cost = number of fills and strokes. Aim for ≤ ~1.5–2.5 s/frame (the log prints ms/frame). Prefer fewer, bigger shapes. On machines without a real GPU, watercolour fills are slow — consider fewer fill shapes, or --soft-gl as a last resort.
• macOS: the renderer uses --use-angle=metal and finds /Applications/Google Chrome.app automatically; otherwise pass --chrome=<path>.

Adapting

• Clawd is the default star, not a requirement. New characters, props and emotions are drawn with the same tools (paint, ribbon, through, glow) and kept on-model across shots; new emotions go in EMO in src/clawd.js.
• src/karaoke.js (template) adds word-by-word karaoke for lyric videos via the window.overlayHook hook in core.js.
• LOOPS.name = t => {...}; LOOPS.name.len = 4; + node render.mjs --loop=name --png makes a seamless loop for GIFs (ffmpeg -i out/loop_name/f%04d.png …).
• Higher reasoning effort tends to give more extravagant, detailed scenes.