Hand Drawn Film

Hand-drawn film

You are making a film that must feel drawn by hand in its marks and its movement. You cannot watch playback, so this skill gives you instruments that turn motion into stills and numbers. Use them after every change. The loop is the method:

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draw keys -> render one still -> build the exposure sheet -> onion / strip the hard action
-> review.mjs -> fix -> full render -> review.mjs on the final -> deliver with limitations

1. Start a project (1 minute)

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node <skill>/scripts/new.mjs ~/films/my-film --ar 16:9 --look pencil --title "My film"
cd ~/films/my-film && npm i --no-audit --no-fund
node render.mjs film.html --grid 24

film.html is a complete, working starter (a ball hops onto a box) with the canonical structure: drawings, one exposure sheet, the shot, a score whose cues read the sheet. Keep the structure, replace the drawings. Fill brief.md first; infer routine choices, ask the user only about decisions that change the film (subject, length, look, format, ending). Needs Node 22+, Chrome, ffmpeg. For looks other than pencil/ink, or photos, sand and paper, start from the matching example in examples/ (table below) and copy its modules locally.

2. Draw (the part that decides quality)

Author each key pose as a whole drawing in SVG path data with svgCel (see redrawn-animation.md and sketch.md).

• Same stroke names in every key; start each stroke at the same landmark; pass points: N so inbetweenCel matches strokes by arc length. A new view, a closed eye or a changed overlap is a replacement drawing (put), never a morph.
• Give closed forms fill: 'paper' so a front shape hides the lines behind it. Stroke order is painter's order: background first, near limbs last. Add an invisible silhouette (opacity: 0, fill: 'paper') first when a body is built from open strokes.
• Line weight: pencil weight 1.8-2.2, value 1.3; ink weight 1.1-1.3. Weight is judged at thumbnail size, not full size. Target ink contrast 110+ in the review table.
• Render each key alone (?pose= pattern in examples/cat-and-mug.html) and look at them side by side before animating. A texture never rescues an unclear silhouette.
• Composition: subject in the middle 60% of the frame, horizon or table around 60-65% down, nothing important within 5% of an edge. Frame with cam() rather than moving every drawing.
• Call setFormat() before any file-scope constant reads W, H, CX, CY. defineFilm() runs last; without this the film is laid out on the 1:1 default (the starter shows the pattern).

3. Animate (exposure sheet)

Use sheetBuilder({library: RAW}): key, between(a, b, spacing(n, kind), frames), hold (optionally {boil: 3, every: 4}), put for replacements, mark('name') for cues. Numbers that work at 24 fps are in craft.md. The short version:

• Moves on twos; fast actions (a swipe, a hit, a fall) on ones; holds 8-24 frames, boiling on fours with keep for eyes and contacts. Never boil on ones.
• Spacing is the acting: slowInOut for most moves, slowIn into a landing or a look, slowOut out of a crouch into a throw or fall, even only for machines and ballistics along the horizontal.
• Anticipation 4-8 frames before any fast action; a settle after it. Give the viewer about one second to read a new idea before the next one starts.
• Props with physics (a falling mug) use formulas on continuous time, not keys. Cue sound from marks (film.time('contact')) so it cannot drift.

4. Look at the motion (every iteration)

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node render.mjs film.html --grid 24          # composition across the film (faithful thumbnails)
node render.mjs film.html --onion 96,16      # one action overlaid blue->red, with a spacing trail
node render.mjs film.html --strip 96,12      # consecutive frames at readable size
node render.mjs film.html --only 96          # one full-size frame for line detail
node review.mjs film.html                    # motion report: pops, flicker, shimmer, blank,
                                             # frozen, faint lines, pacing, exposure per scene

Read review.md for how to interpret each finding. In an onion, the dots are the ink centroid per frame: evenly spaced dots are even spacing, bunched dots are a slow in or out, a straight chain on a jump means the arc is missing. Fix every warn or state why it is intended; confirm each finding by eye with --strip around the frame. The numbers are measurements, not taste.

5. Deliver

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node render.mjs film.html                    # frames, mp4, contact sheet, -final.mp4 with score
node review.mjs film.html                    # on the finished film

Full renders run on parallel browser processes (--jobs N) and are bit-identical to serial renders. Deliver the source folder, the MP4, the contact sheet, the review report and a short list of known limitations. Verify duration, dimensions and frame count (ffprobe). Never call a film finished because code or checks passed; say what you looked at (onions, strips, stills) and that you did not watch it at speed if you could not.

Choose references by task

scenes.md and reference-films.md hold optional scene devices and historical references, not required structures.

Invariants

• 24 fps by default. Scenes get continuous tau; quantize a pose once (twos(t) or an exposure sheet), never twice. Camera and physics usually run on ones.
• No output-frame seeds. A held drawing holds its marks; a boil is a finite set of drawings. Every frame must reproduce after seeking (render workers depend on it).
• Contacts stay planted until their planned release; IK clamps and reports unreachable targets.
• Record sources and licences for external media (photos, fonts).
• Engine edits belong in the skill's assets/, then get copied to films; do not fork core.js inside one film.

Quality gates

• Drawing: clear silhouette at 240 px; consistent proportions across keys; line hierarchy (outer contour heavier than interior detail); purposeful taper and gaps; no accidental tangents; front forms hide what is behind them.
• Motion: readable keys, anticipation and settle where the action needs them, deliberate spacing (check the onion), planted contacts, no pops or two-drawing flicker in the review.
• Material: texture tied to the paper or object, not the screen; no shimmer unless intended; line contrast 110+ at thumbnail size for line films.
• Delivery: no page errors, no unintended blank frames, the ending holds 0.5-1.5 s, text and cards stay up long enough to read (about 3 words per second plus one second), the encoded MP4 decodes and has the expected frame count.

node scripts/verify.mjs runs the engine's regression suite (20 checks) after engine edits.