OffscreenCanvas-placeholder-image-source-with-worker.html

<!DOCTYPE html>
<title>Test using a placeholder canvas as an image source.</title>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>

<script id='myWorker' type='text/worker'>
var ctx;
self.onmessage = function(msg) {
  ctx = msg.data.getContext('2d');
  ctx.fillStyle = '#0f0';
  ctx.fillRect(0, 0, 100, 100);
  requestAnimationFrame(() => {
    self.postMessage("done");
  });
};
</script>

<script>
var t = async_test("Test that using a placeholder canvas as a source image accesses the image that was committed to the associated OffscreenCanvas in a worker.");
var canvas = document.createElement('canvas');
canvas.width = 100;
canvas.height = 100;
var offscreen = canvas.transferControlToOffscreen();

var blob = new Blob([document.getElementById('myWorker').textContent]);
var worker = new Worker(URL.createObjectURL(blob));
worker.postMessage(offscreen, [offscreen]);
worker.addEventListener('message', msg => {
  // the message is a synchronization barrier that guarantees
  // that the offscreen commit has been processed on the worker thread.
  verifyImage(canvas, "verify that drawImage works with placeholder canvas as a source.");
  var testImage = new Image();
  testImage.src = canvas.toDataURL();
  testImage.onload = function() {
    verifyImage(canvas, "verify that toDataURL works on placeholder canvas.");
    canvas.toBlob(blob => {
      createImageBitmap(blob).then(image => {
      	verifyImage(image, "verify that toBlob works on placeholder canvas.");
      	t.done();
      })
    });
  }
});

function verifyImage(image, description) {
  var testCanvas = document.createElement('canvas');
  var testCtx = testCanvas.getContext('2d');
  testCtx.drawImage(image, 0, 0);

  t.step(function() {
    var pixel = testCtx.getImageData(50, 50, 1, 1).data;
    assert_array_equals(pixel, [0, 255, 0, 255], description);
  });
}
</script>
chromium/third_party/blink/web_tests/fast/canvas/OffscreenCanvas-placeholder-image-source-with-worker.html
