LayoutTests/fast/canvas/offscreencanvas-in-shared-worker-readback.html

<!DOCTYPE html><!-- webkit-test-runner [ OffscreenCanvasEnabled=true ] -->
<html>
<head>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
</head>
<body>
<script>
promise_test(async () => {
    const worker = new SharedWorker("resources/offscreencanvas-readback-shared-worker.js");
    const result = await new Promise((resolve, reject) => {
        worker.port.onmessage = e => resolve(e.data);
        worker.onerror = e => reject(new Error(e.message || "shared worker error"));
        worker.port.start();
        worker.port.postMessage("RUN");
    });
    assert_equals(result.error, undefined, "worker drew and read back the canvas without throwing");
    assert_array_equals(result.topLeft, [0, 255, 0, 255], "top-left pixel is the drawn green tile");
    assert_array_equals(result.bottomRight, [255, 0, 0, 255], "bottom-right pixel is the red fill");
}, "OffscreenCanvas draw + getImageData readback in a shared worker");
</script>
</body>
</html>