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fix: Prevent hero effect from exceeding white and triggering HDR #3294

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fix: Prevent hero effect from exceeding white and triggering HDR #3294

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4f61353
fix: Prevent hero effect from exceeding white and triggering HDR
iwoplaza Oct 29, 2026
d45bc1b
refactor: Use dark mode flag instead of querying page background
iwoplaza Oct 29, 2026
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24 changes: 22 additions & 2 deletions apps/typegpu-docs/src/components/hero-effect/hero-effect.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,14 @@ const Uniforms = d.struct({
modelMatrix: d.mat4x4f,
});

// Page backgrounds (in sRGB) the canvas is composited onto, matching `bg-white` and `bg-navy-bg`
const lightBackground = d.vec3f(1);
const darkBackground = d.vec3f(35 / 255, 39 / 255, 54 / 255);

function isDarkMode() {
return document.documentElement.dataset.theme === 'dark' ? 1 : 0;
}

export async function initHeroEffect(options: HeroEffectOptions) {
const { root, context } = options;
const canvas = context.canvas as HTMLCanvasElement;
Expand All @@ -32,6 +40,7 @@ export async function initHeroEffect(options: HeroEffectOptions) {
}

const uniforms = root.createUniform(Uniforms);
const darkMode = root.createUniform(d.u32, isDarkMode());
const fsampler = root.createSampler({
minFilter: 'linear',
magFilter: 'linear',
Expand Down Expand Up @@ -140,8 +149,17 @@ export async function initHeroEffect(options: HeroEffectOptions) {
);

const grayscale = d.vec4f(d.vec3f(c2.x + c2.y + c2.z + 0.8) * tint, 1) * 0.5 * c2.w;

return std.mix(grayscale, c2, std.smoothstep(0, 0.2, downSample));
const result = std.saturate(std.mix(grayscale, c2, std.smoothstep(0, 0.2, downSample)));

// The canvas is premultiplied, and the effect relies on color exceeding alpha (additive light).

@cieplypolar cieplypolar Oct 30, 2026

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I am not sure if this is a good idea that the effect relies on undefined behavior (source).

Clamping against the page background does not guarantee that color <= alpha.
See:

Image

Legend:

  • x -> alpha
  • y -> color
  • b -> arbitrary channel from background color

// The compositor outputs `color + background * (1 - alpha)`, which can go above 1.0 and
// make the display switch to HDR. Clamping against the page background keeps it within range.
let background = d.vec3f(lightBackground);
if (darkMode.$ === 1) {
background = d.vec3f(darkBackground);
}
Comment on lines +157 to +160

@cieplypolar cieplypolar Oct 30, 2026

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Suggested change
let background = d.vec3f(lightBackground);
if (darkMode.$ === 1) {
background = d.vec3f(darkBackground);
}
const background = darkMode.$ === 1 ? d.vec3f(darkBackground) : d.vec3f(lightBackground);

const maxColor = 1 - background * (1 - result.w);
return d.vec4f(std.min(result.xyz, maxColor), result.w);
});

const postProcessPipeline = root.createRenderPipeline({
Expand All @@ -165,6 +183,7 @@ export async function initHeroEffect(options: HeroEffectOptions) {
}

fluidSim.update(timestamp);
darkMode.write(isDarkMode());

const viewProjection = mat4.perspective(
0.5,
Expand Down Expand Up @@ -236,6 +255,7 @@ export async function initHeroEffect(options: HeroEffectOptions) {
fluidSim.destroy();
screenTextures.destroy();
uniforms.buffer.destroy();
darkMode.buffer.destroy();
model.destroy();
},
};
Expand Down
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