Impasto · Palette Knife — our demo

One example among many. Don't reuse its story, arc, shots, props or timings.

Demo: The Colour of Rain (39.7 s) · impasto.mp4 · source in demo/

Story & structure

A grey square in the rain. A street cellist plays and nobody stops; halfway through he gives up. A little girl opens a red umbrella in front of him: the film's first colour. The cello starts again as a waltz, and umbrella after umbrella turns to colour on the beat. From overhead, the crowd's waltz paints a coloured mandala on the cobbles. The last chord lands, the rain stops, colour fills the whole square.

Arc: loneliness (grey) → giving up (silence) → one touch of colour (the red umbrella) → being heard (the waltz) → the crowd (overhead choreography) → echo (same camera, grey turned to colour; the phrase that broke off on E resolves to D).

Why it fits the medium: colour is the story, and the knife can re-lay any stroke in a new colour. It is a music film with no narration: the title is laid in with the knife over the grey sky and washed off by the rain (it drifts down and fades).

Native moves spent: colour re-laid by the knife (the umbrella opening, the cellist's recovery, the final chord filling the square); the one coloured thing (the red umbrella is the only colour in the first half); motion paints the picture (overhead, each umbrella drips its colour along its path, and the pull-back reveals a mandala); raking light (the sun grazes the ground at the final chord, then settles); paint-over transitions with a knife scrape.

Shots

#	Time	Shot / camera	Why
1	0–2.65	CU cello body + bow, slight push	3 s hook: the only colour in the grey world is the note (an amber ribbon), soon washed out by the rain
2	2.65–7.15	Extreme wide, slow truck + push, paint-over in	The world: grey square, people hurrying. Title knifed in, then carried away by the rain
3	7.15–12.4	Medium, one continuous push through the silence	Nobody stops: passers-by cross close to camera and block him; push to his face as he gives up
4	12.18–16.66	Low CU on a puddle → tilt-up, hard cut	A boot lands on the splash; up to her, him, the umbrella; anticipation, POP, impact zoom
5	16.66–19.39	Face CU → pull-back, hard cut on the downbeat	He looks up, lifts the bow; at 18.03 the bow lands and colour pours out of the cello
6	19.39–23.48	Closer framing of the same wide, paint-over	The ribbon carries colour to each umbrella, one per beat
7	23.48–31.66	Overhead, rotating + crane-out	Signature shot: choreography and the coloured trails on the ground
8	31.66–35.75	Extreme wide (same set-up as 2), push toward the arch	Rhyme with the opening: grey to colour, raking light, umbrellas closing, birdsong
9	35.75–39.66	End card, paint-over	Title, a red dot (an umbrella seen from above), credits

Six moves (push, truck, tilt-up, pull, rotate, crane-out overhead); sizes from CU to extreme wide and overhead. The same wide camera serves the opening (grey), the middle (umbrellas in colour) and the finale (all colour): for this story, the change was the story. Keep the camera inside the painted plate.

Score structure

demo/timeline.js holds the grids; picture and score both read it.

Part A: solo cello, D minor, 3/4 at 80 BPM from 0.4 s. The phrase stops on an unresolved E3 at 10.15 s; the bow leaves the string 0.3 s later.
Silence 10.45–12.4: rain nearly gone, one drip at 11.15, two small steps at 11.5 / 11.95 enter before the picture (J-cut), a big splash at 12.4 is the first sound after it.
Part B: street-musette waltz, D major, 3/4 at 132 BPM.
15.3 POP (pickup bar): glockenspiel + rising harp glissando.
16.66 accompaniment enters: pizzicato bass + accordion "oom-pah-pah".
18.03 the cello melody enters.
19.39–23.03 nine umbrellas, one per beat; glockenspiel pitches climb G→B→D / A→C#→E / D→F#→A.
23.48–31.21 overhead, six bars of choreography; accordion repeats the melody an octave up, one harp arpeggio per bar.
31.21 grand pause, digital zero; the rain freezes in the air.
31.66 final chord (tutti + timpani + suspended cymbal).
Coda F#→E→D resolves the phrase that broke off at the start.
35.75 last pizzicato, end card.
Other voices: violin pizz, shaker.

Sound design, section by section:

Section	Bed	Foley	Music
CU	rain (slightly distant)	bow rosin, raindrops on varnished wood	the solo's first note
Grey square	full rain + gutter trickle	wet cobble footsteps (placed by the walk algorithm, panned), knife scrape on the title	solo
Medium	rain under the arcade (low-passed)	passers-by footsteps close + umbrella fabric brushing	solo, breaks off
Silence	almost nothing	one drip, small steps (J-cut), big splash	none
Girl	rain	nylon rustle, rib click, umbrella "fwump", paint dabs landing	POP
Reaction	muffled rain	bow-lift air	accompaniment, then cello
Street	rain (lowered)	each umbrella's "fwump" + a soft hiss as the ribbon arrives	waltz + glockenspiel arpeggios
Overhead	rain	the crowd's water steps on the waltz (beat 1 heavy)	tutti
Grand pause	digital zero	—	—
Ending	rain stopped	drips, umbrellas closing, birdsong	chord → coda

Palette-knife scrapes sit on every repaint.

Palette & props

After-rain sunset sky: cobalt #34507e → peach #d99a78 → gold #f7dca0. Facades ochre #dca064 and rose #c98d7e, shutter green #3f7a6c, awning red #b8342a.
Umbrellas at full chroma: cadmium red #dc2f28, yellow #f4bc2a, cobalt #2f62c0, viridian #23906c, magenta #cc3a82, orange #ee7a2a, turquoise #26aab4, violet #6e4cc0.
Grey world = luminance of the same strokes, slightly cool, 5 % colour residue; its specular is slightly higher (wet).
Light: light [-.55,-.6,.7], norm 3.2, amb .8, dif .28, spec .16–.3, ao 1.2.
Stroke sizes: 40–60 px planes in sky and walls, 3–6 px only at edges and faces. Knife stroke: skew ±0.55, angle jitter ±13°, value jitter ±6 %. Figures and umbrellas use run: 0–0.25 so they stay solid.
Figures: the cellist (IK bow arm, bow direction changes on each note), the girl (dips the umbrella before it snaps open), the crowd (rings swell on every downbeat; umbrellas pop on beats with a scale bounce and a burst of paint dabs, swing down to hang after closing). Faces: eyes, brows and mouth are separate procedural strokes so they can act.
Wet reflections: stacks of short horizontal dabs under each lamp and window.

End card

Knife-painted title on deep ultramarine, a red dot (an umbrella from above), and crisp DOM text for the credits (small text must stay legible): "an impasto palette-knife study", then "Lemo-Opuscar · LemoLab × Claude Opus 5.5", then the sample and font credits. The "LemoLab × Claude Opus 5.5" sign-off belongs to this library's demo only; a user's film carries no LemoLab credit and no copy of this card (the line lives in demo/film.js: remove it if you adapt that file).

Build notes

styles/impasto/demo/
  engine/impasto.js  WebGL2 knife-stroke renderer     engine/plate.js  reference illustration → strokes
  timeline.js        BPM grids, cut times, melodies (MEL_A, MEL_B), pops
  scenes/*.js        sets as reference illustrations (Ref.fill/line/text/tint) → paintRef()
  film.js            shots, cameras, transitions (EDIT table), post looks, end card
  music/score.py     sampler score (CC0 instruments)   mix.py  foley + ambience + ducking + true silence
  tools/dump_timeline.mjs  timeline → out/timeline.json    build.sh

timeline.js first: BPM grids, cut times, melodies, pops. tools/dump_timeline.mjs writes out/timeline.json for the score.
Sets in scenes/*.js → paintRef().
film.js: shots, cameras, transitions, post.
music/score.py, then mix.py.
sh styles/impasto/demo/build.sh renders everything (≈ 30 s of GPU render for 952 frames), muxed with grain 0.

Engine-level traps: half is a reserved word in GLSL ES 3.00; binding the composite quad while a stroke VAO is still bound silently rewires attribute 0 ("vertex buffer not big enough" on the next frame): unbind the VAO first.

Pitfalls tied to this demo's props: - Keep the umbrella radius at 0.34 × body height: 0.46 looks like a parasol table. - Coats as plain rectangles read as bollards: A-line taper + lit edge + shoulder dab + hair dab. - Use a per-shot index in the per-shot ribbon loop: a global index flings control points off-screen (a streak from the sky). - Paint the ground before the buildings: painted after, it covers their feet.

Engine reference

demo/engine/impasto.js (renderer) and demo/engine/plate.js (reference → strokes).

API	What it does
`new Impasto(canvas, {W, H, ss})`	WebGL2 renderer, supersampled colour + height buffers
`E.begin()` / `E.finish(post)`	start a frame / light + grade (`light, norm, amb, dif, spec, ao, expo, sat, vig…`)
`E.batch(Float32Array)` → `E.draw(batch, o)`	static stroke set. `o = {M, cam:{x,y,zoom,rot}, t, grey, reveal, revDur, appear, appDur, alpha, run, hgt}`
`E.drawNow(Float32Array, o)`	transient strokes (figures, weather, ribbons)
`E.texture(canvas)` + `E.under(tex, w, h, o)`	thin underpainting (supports `revC:[x,y,speed]` reveal wave)
`new Strokes().push({x,y,ang,len,wid,c,c2,type,taper,bend,skew,alpha,hgt,rev,app,seed})`	build strokes; `type`: `KNIFE`, `BRUSH`, `DAB`, `LINE`
`new Ref(w, h, scale)` + `.fill(path, fill, props)` / `.line` / `.text` / `.tint`	reference illustration; props `{dir, maxR, detail, group, type, hgt, jit, len, wid, aj, fallback}`
`paintRef(ref, {R:[radii], T, rev(x,y), app(x,y,level)})`	coarse→fine knife strokes confined to shape groups
`strokePath(out, pts, {wid, c, type, step})`	strokes along a polyline