canvas-no-clear-on-readpixels.html

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<head>

<meta charset="utf-8">

<title>Check that the canvas is NOT recomposited after calling readPixels</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>

<style>

canvas {

    border: 1px solid black;

.correct {

    border: 1px solid black;

    background-color: #00ff00;

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<body>

<pre>

This test must be run manually.

This test tests that a canvas is NOT cleared

and recomposited after calling readPixels.

You should see a <span class="correct">green rectangle</span>

with black a outline on success.

</pre>

<canvas id='c'></canvas>

<div id="console"></div>

<script>

"use strict";

var wtu = WebGLTestUtils;

var c = document.getElementById("c");

var gl = wtu.create3DContext(c);

gl.clearColor(0,1,0,1);

gl.clear(gl.COLOR_BUFFER_BIT);

wtu.waitForComposite(function() {

  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array(4));

  wtu.glErrorShouldBe(gl, gl.NO_ERROR, "no errors");

});

</script>

</body>

</html>