WebGPU画像シェーダーでレンズ効果を再現 2025 — ローパワーデバイス最適化ガイド

graph LR
    A[Source Texture] --> B[Compute Shader: Bright Spot Detection]
    B --> C[Compute Shader: Flare Tile Accumulation]
    C --> D[Render Pass: Bokeh & Bloom]
    D --> E[Post Processing: Tone Mapping]
    E --> F[Canvas / Texture Output]

const adapter = await navigator.gpu.requestAdapter({ powerPreference: 'low-power' })
const device = await adapter?.requestDevice({
  requiredFeatures: ['timestamp-query'],
  requiredLimits: { maxTextureDimension2D: 4096 }
})
const context = canvas.getContext('webgpu')!
context.configure({
  device,
  format: navigator.gpu.getPreferredCanvasFormat(),
  alphaMode: 'premultiplied'
})

// shaders/bright-spot.wgsl
@group(0) @binding(0) var<storage, read> inputImage: array<vec4<f32>>;
@group(0) @binding(1) var<storage, read_write> brightMask: array<f32>;

@compute @workgroup_size(16, 16)
fn main(@builtin(global_invocation_id) global_id: vec3<u32>) {
  let idx = global_id.y * textureWidth + global_id.x;
  if (idx >= arrayLength(&inputImage)) { return; }
  let color = inputImage[idx];
  let luminance = dot(color.rgb, vec3<f32>(0.299, 0.587, 0.114));
  brightMask[idx] = select(0.0, luminance, luminance > params.threshold);
}

// shaders/flare-accumulate.wgsl
@group(0) @binding(0) var<storage, read> brightMask: array<f32>;
@group(0) @binding(1) var<storage, read_write> flareTiles: array<vec4<f32>>;

@compute @workgroup_size(8, 8)
fn main(@builtin(workgroup_id) group_id: vec3<u32>) {
  let tileIndex = group_id.y * tileCountX + group_id.x;
  var sum = vec4<f32>(0.0);
  for (var y = 0u; y < TILE_SIZE; y = y + 1u) {
    for (var x = 0u; x < TILE_SIZE; x = x + 1u) {
      let idx = (group_id.y * TILE_SIZE + y) * textureWidth + (group_id.x * TILE_SIZE + x);
      sum += vec4<f32>(brightMask[idx]);
    }
  }
  flareTiles[tileIndex] = sum / f32(TILE_SIZE * TILE_SIZE);
}

// pipeline/render.ts
const flarePipeline = device.createRenderPipeline({
  vertex: { module: device.createShaderModule({ code: quadVert }) },
  fragment: {
    module: device.createShaderModule({ code: flareFrag }),
    targets: [{ format: contextFormat }]
  },
  primitive: { topology: 'triangle-list' }
})

commandEncoder.beginRenderPass({
  colorAttachments: [{
    view: context.getCurrentTexture().createView(),
    loadOp: 'load',
    storeOp: 'store',
    clearValue: { r: 0, g: 0, b: 0, a: 1 }
  }]
})

// shaders/flare.frag.wgsl
@group(0) @binding(0) var flareSampler: sampler;
@group(0) @binding(1) var flareTexture: texture_2d<f32>;
@group(0) @binding(2) var blurTexture: texture_2d<f32>;

@fragment
fn main(@builtin(position) pos: vec4<f32>) -> @location(0) vec4<f32> {
  let uv = pos.xy / vec2<f32>(canvasSize);
  let flare = textureSample(flareTexture, flareSampler, uv);
  let blur = textureSample(blurTexture, flareSampler, uv);
  return mix(flare, blur, params.blurMix) * params.intensity;
}

const querySet = device.createQuerySet({ type: 'timestamp', count: 2 })
passEncoder.writeTimestamp(querySet, 0)
// ... render operations ...
passEncoder.writeTimestamp(querySet, 1)

.hero-visual {
  background-image: url('/images/hero-static.png');
}

@media (prefers-reduced-motion: no-preference) {
  .hero-visual {
    background-image: none;
    canvas { display: block; }
  }
}