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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>OffscreenCanavs context attribute preserveDrawingBuffer</title>
<link rel="stylesheet" href="../../resources/js-test-style.css"/>
<script src="../../js/js-test-pre.js"></script>
<script src="../../js/webgl-test-utils.js"></script>
<script src="../../js/tests/canvas-tests-utils.js"></script>
</head>
<body>
<div id="description"></div>
<div id="console"></div>
<script>
"use strict";
description("This test checks whether OffscreenCanvas webgl context honors the preserveDrawingBuffer flag.");

function getPixelsFromOffscreenWebgl(preserveFlag) {
  var canvas = document.createElement("canvas");
  var offscreenCanvas = transferredOffscreenCanvasCreation(canvas, 10, 10);
  var gl = offscreenCanvas.getContext("webgl", {preserveDrawingBuffer: preserveFlag});

  // Draw some color on gl and commit
  gl.clearColor(1, 0, 1, 1);
  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.commit();

  var pixels = new Uint8Array(4);
  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
  return pixels;
}

if (!window.OffscreenCanvas) {
    testPassed("No OffscreenCanvas support");
} else {
    // Test if OffscreenCanvas.webgl retains context if preserveDrawingBuffer is true.
    var pixelsPreserve = getPixelsFromOffscreenWebgl(true);
    shouldBe(pixelsPreserve, [255,0,255,255]);

    // Test if OffscreenCanvas.webgl loses context if presereDrawingbuffer is false.
    var pixelsNoPreserve = getPixelsFromOffscreenWebgl(false);
    shouldBe(pixelsNoPreserve, [0,0,0,0]);
}

var successfullyParsed = true;

</script>
<script src="../../js/js-test-post.js"></script>
</body>
</html>
