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No.97 · Backgrounds

Dither Flow

Slow folds of satin light printed in four tones with an ordered dither on a coarse pixel grid; the pointer stirs a swirl into the folds.

The prompt

Written for the variant you picked above: Violet

Write a WebGL1 full-screen fragment shader background (one triangle, no libraries) that looks like flowing satin rendered on a one-bit-ish pixel screen. Quantise first: floor(gl_FragCoord / cell) gives a pixel cell (2 CSS px × DPR); every value is evaluated at the cell centre, so the whole image is made of crisp square pixels. The field is three-octave value-noise fBm, domain-warped twice (q from p, r from p + 1.7q, h from p + 1.5r) and drifting slowly with time, treated as the height of folded cloth: take finite differences for a normal, light it from the upper left, and use pow(diffuse, 4.6) plus a pow-36 specular, so ridges catch thin bright lines and the far sides of folds fall into shadow; a smoothstep on the height drops whole regions to the ground colour. Brightness 0–1 is split into four tones (ground, body, light, crest); between two neighbouring tones each cell picks the lighter one when the fractional part beats its 4×4 Bayer threshold, giving the ordered-dither stipple along every gradient. The pointer adds a slow swirl: points near it rotate around it by up to 1.4 rad with a Gaussian falloff, the strength and centre eased so the folds bend gently toward wherever you move. Render at about 30fps (the motion is slow), stop when offscreen or in a hidden tab, draw a single frame under reduced motion, skip the pointer on touch, and fall back to CSS radial gradients from the same palette without WebGL. Children sit above the canvas. Selected variant — Violet: Palette [#09090b ground, #4b2bff body, #a996ff light, #ffffff crest]: electric violet folds with white highlights on black, as in a late-night poster.

Notes

Interaction
The pointer stirs a slow swirl into the folds; there is nothing to click.
Motion
Field time 0.035 per second with a 0.12 fold phase; pointer centre lerp 0.06 and swirl strength lerp 0.04; about 30fps.
Accessibility
Decorative and aria-hidden; put text on it with your own contrast check — the crest tone is near white. Reduced motion renders one still frame.
Responsive
Fills its container; the pixel cell stays the same CSS size at any width, DPR capped at 2.
On touch
No pointer swirl on touch; the folds keep drifting on their own.

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301 components