0xrsydn
169c5f9b63
Spec fixes come from a test where pi + deepseek-v4.1-flash wrote effects from EFFECTS.md alone: glitch-blocks and ghost-stamps both compiled on the first try. The agent's feedback led to in.dt (frame time), documented limits of in.prev as memory, and a --check warning for ignored slider lines. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
34 lines
1.6 KiB
Metal
34 lines
1.6 KiB
Metal
// Every `stamp` seconds the moving parts of the picture are frozen in place as a translucent,
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// tinted ghost; each ghost fades over `life` seconds, so moving things leave a row of copies.
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// order 70
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// slider stamp 0.2 3.0 0.5
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// slider life 0.2 6.0 2.0
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// slider hue 0.0 1.0 0.55
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// hue 0..1 -> a fully saturated colour (0 red, 0.08 orange, 0.33 green, 0.66 blue)
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static float3 hueColor(float h) {
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return clamp(abs(fract(h + float3(0.0, 2.0 / 3.0, 1.0 / 3.0)) * 6.0 - 3.0) - 1.0, 0.0, 1.0);
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}
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float4 effect(float2 uv, Inputs in) {
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// The frozen ghosts are one number per pixel (a tinted brightness), so they live in the
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// alpha channel of this effect's own output. The colour is only added when displaying, so
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// `in.prev.rgb` never feeds the live picture back into itself.
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float ghosts = in.prev.sample(in.smp, uv).a;
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float frame = in.dt;
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ghosts *= exp(-frame / max(in.p.life, 0.05));
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float3 live = in.image.sample(in.smp, uv).rgb;
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float diff = length(in.camera.sample(in.smp, uv).rgb - in.last.sample(in.smp, uv).rgb);
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float moving = smoothstep(0.03, 0.30, diff);
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float fresh = dot(live, float3(0.299, 0.587, 0.114)) * moving;
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// A stamp is taken just after each `stamp`-second slot of in.time begins. The window is two
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// frames wide, so a stamp is not missed when the frame rate falls below the nominal one.
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float slot = max(in.p.stamp, 0.05);
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float begins = 1.0 - step(2.0 * frame / slot, fract(in.time / slot));
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ghosts = max(ghosts, fresh * begins);
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float3 tint = hueColor(in.p.hue);
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return float4(live + tint * ghosts * 0.85, ghosts);
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}
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