LayoutTests/compositing/canvas/hidpi-canvas-backing-store-invalidation-2.html

<!DOCTYPE HTML>
<html>
<head>
<meta name="viewport" content="initial-scale=1">
<script>

if (window.testRunner) {
  testRunner.dumpAsText();
  testRunner.waitUntilDone();
}

function doTest() {
  var canvasElement = document.getElementById("canvas");
  let dpr = window.devicePixelRatio || 1;

  canvas.width *= dpr;
  canvas.height *= dpr;

  canvas.style.transform = "scale(" + 1/dpr + ", " + 1/dpr + ")";

  let ctx = canvas.getContext('2d');
  ctx.scale(dpr, dpr);

  ctx.fillStyle = 'green';
  ctx.fillRect(0, 0, 1000, 500);
    
  if (window.testRunner) {
    document.getElementById('layers-before').innerText = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_DEVICE_SCALE);
  }

  requestAnimationFrame(function() {
    if (window.internals) {
      window.internals.setPageScaleFactor(0.5, 0, 0);
    }

    if (window.testRunner) {
      document.getElementById('layers-after').innerText = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_DEVICE_SCALE);
      testRunner.notifyDone();
    }
  });
}

window.addEventListener('load', doTest, false);
</script>
</head>

<body>
<p> Tests whether we switch back to a hidpi backing store when we zoom out (and would otherwise downscale the content too much).</p>
<div style="opacity:0.5">
<canvas id="canvas" width="1000" height="500" style="transform-origin:top left"></canvas>
</div>
<pre id="layers-before">Initial layer tree goes here in DRT</pre>
<pre id="layers-after">Mutated layer tree goes here in DRT</pre>
</body>

</html>