Function getScreenshotStats

e2e/webgpu-psnr-app.spec.ts:728–770

(page: Page, png: Buffer)

}

async function getScreenshotStats(page: Page, png: Buffer): Promise<ScreenshotStats> {
  return page.evaluate(async (base64) => {
    const image = new Image();
    const loaded = new Promise<void>((resolve, reject) => {
      image.onload = () => resolve();
      image.onerror = () => reject(new Error('Failed to decode screenshot'));
    });
    image.src = `data:image/png;base64,${base64}`;
    await loaded;

    const canvas = document.createElement('canvas');
    canvas.width = image.naturalWidth;
    canvas.height = image.naturalHeight;
    const context = canvas.getContext('2d');
    if (!context) throw new Error('Failed to create screenshot stats canvas context');
    context.drawImage(image, 0, 0);
    const pixels = context.getImageData(0, 0, canvas.width, canvas.height).data;
    let visiblePixelCount = 0;
    let nonBlackPixelCount = 0;
    let lumaSum = 0;
    for (let index = 0; index < pixels.length; index += 4) {
      const alpha = pixels[index + 3];
      if (alpha === 0) continue;
      visiblePixelCount += 1;
      const red = pixels[index];
      const green = pixels[index + 1];
      const blue = pixels[index + 2];
      const luma = 0.2126 * red + 0.7152 * green + 0.0722 * blue;
      lumaSum += luma;
      if (red + green + blue > 8) {
        nonBlackPixelCount += 1;
      }
    }

    return {
      width: canvas.width,
      height: canvas.height,
      visiblePixelCount,
      nonBlackPixelCount,
      meanLuma: visiblePixelCount > 0 ? lumaSum / visiblePixelCount : 0,
    };
  }, png.toString('base64'));
}

async function captureNonBlankSceneCenterSamplesUntilWebGpu(
  page: Page,