gfx/tests/reftest/1972885.html

   1 <!DOCTYPE html>
   2 <html class="reftest-wait">
   3 <meta charset="utf-8">
   4 <title>Test for Bug 1972885</title>
   5 <style>
   6 body {
   7   margin: 0;
   8 }
   9 canvas {
  10   /* Height would round up to 101px, but subpixel snaps to 100. */
  11   margin-top: 1.6px;
  12   width: 100px;
  13   height: 100.5px;
  14 }
  15 </style>
  16 <canvas id="canvas"></canvas>
  17 <script>
  18 function draw(canvas, width, height) {
  19   const ctx = canvas.getContext('2d');
  20   canvas.width = width;
  21   canvas.height = height;
  22   const imgData = ctx.createImageData(width, height);
  23   const u32View = new Uint32Array(imgData.data.buffer);
  24   u32View.fill(0xFFFFFFFF);
  25   for (let y = 0; y < height; y += 2) {
  26     for (let x = 0; x < width; x++) {
  27       u32View[y * width + x] = 0xFF000000;
  28     }
  29   }
  30   ctx.putImageData(imgData, 0, 0);
  31 }
  32
  33 const ro = new ResizeObserver((entries) => {
  34   for (const entry of entries) {
  35     if (entry.target !== canvas) {
  36       continue;
  37     }
  38     draw(
  39       canvas,
  40       entry.devicePixelContentBoxSize[0].inlineSize,
  41       entry.devicePixelContentBoxSize[0].blockSize);
  42   }
  43   document.documentElement.removeAttribute("class");
  44 });
  45
  46 // Get the properly subpixel snapped size through ResizeObserver.
  47 ro.observe(canvas);
  48 </script>