From 95802739b8ccaf9112fe4fe6e496ba7ae4158aae Mon Sep 17 00:00:00 2001 From: skal Date: Fri, 6 Mar 2026 22:53:29 +0100 Subject: feat(effects): add Scratch post-process effect with reusable scratch_lines snippet - src/shaders/render/scratch_lines.wgsl: reusable WGSL snippet registered as "render/scratch_lines"; call scratch_lines(uv, resolution, time)->f32 from any effect. Uses hash_1f from math/noise; 8 lines/frame, ~24fps flicker. - src/effects/scratch.{wgsl,h,cc}: thin Scratch effect wrapping the snippet. - Applied to "intro" and "rotating_cube" sequences as the final step. - 35/35 tests passing. handoff(Gemini): Scratch effect added. render/scratch_lines snippet is reusable. Co-Authored-By: Claude Sonnet 4.6 --- src/shaders/render/scratch_lines.wgsl | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100644 src/shaders/render/scratch_lines.wgsl (limited to 'src/shaders') diff --git a/src/shaders/render/scratch_lines.wgsl b/src/shaders/render/scratch_lines.wgsl new file mode 100644 index 0000000..04ed6f8 --- /dev/null +++ b/src/shaders/render/scratch_lines.wgsl @@ -0,0 +1,35 @@ +// Horizontal film scratch lines utility +// Returns scratch intensity [0,1] to additively overlay on a color buffer. +// +// Parameters: +// uv - normalized texture coordinates [0,1] +// resolution - screen size in pixels (used for sub-pixel thickness) +// time - physical time in seconds +// +// Simulates aged/damaged film: ~8 random horizontal lines per frame, +// each with independent position, thickness, brightness and on/off state. +// Time is quantized to 24 buckets/sec so scratches flicker like film frames. +#include "math/noise" + +fn scratch_lines(uv: vec2f, resolution: vec2f, time: f32) -> f32 { + // Quantize to ~24fps to simulate film frame rate + let t = floor(time * 24.0); + + var intensity = 0.0; + for (var i = 0; i < 8; i++) { + let seed = f32(i) * 17.3 + t; + // ~25% chance this scratch is visible this frame + let visible = step(0.75, hash_1f(seed + 3.1)); + // Random vertical position [0, 1] + let y = hash_1f(seed + 7.9); + // Thickness in pixels [1, 4] + let thickness = hash_1f(seed + 13.5) * 3.0 + 1.0; + // Brightness [0.5, 1.0] + let brightness = hash_1f(seed + 21.7) * 0.5 + 0.5; + // Soft linear falloff from line center + let dy = abs(uv.y - y) * resolution.y; + let line = clamp(1.0 - dy / thickness, 0.0, 1.0); + intensity += line * brightness * visible; + } + return clamp(intensity, 0.0, 1.0); +} -- cgit v1.2.3