<!DOCTYPE HTML>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script>
test(function() {
    var offscreenCanvas = new OffscreenCanvas(100, 50);
    var ctx = offscreenCanvas.getContext('2d');
    ctx.fillStyle = "#0f0";
    ctx.fillRect(0, 0, 100, 50);
    // The default globalCompositeOperation is source-over, that that will
    // draw nothing in the next drawImage call. So we have to change it to copy
    // so that it will actually draw transparent black in the next drawImage
    // call.
    ctx.globalCompositeOperation = 'copy';
    
    var offscreenCanvas2 = new OffscreenCanvas(100, 50);
    ctx.drawImage(offscreenCanvas2, 0, 0);

    var clr = ctx.getImageData(50, 25, 1, 1).data;
    assert_array_equals(clr, [0, 0, 0, 0]);
}, 'Use OffscreenCanvas without a context as ImageSource should draw transparent black');
</script>