content/canvas/test/reftest/webgl-clear-test.html

<!DOCTYPE html>
<html class="reftest-wait">
<head>
<meta charset="UTF-8">

<script type="text/javascript" src="webgl-utils.js"></script>
<script type="text/javascript">
/* Clear Test
 *
 * Clear the canvas to green to test that we get pixels to the screen.
 */

"use strict";

function renderGL(gl) {
  gl.clearColor(0.0, 1.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.finish();
}

function renderBackup(canvas) {
  var context = canvas.getContext("2d");
  context.fillStyle = "rgba(0, 255, 0, 1.0)";
  context.fillRect(0, 0, 256, 256);
}

function runTest() {
  var canvas = document.getElementById("canvas");
  var gl = initGL(canvas);

  if (gl)
    renderGL(gl);
  else
    renderBackup(canvas);

  rAF(testComplete);
}

function testComplete() {
  document.documentElement.removeAttribute("class");
}
</script>
</head>

<body onload="rAF(runTest);">
  <canvas id="canvas" width="256" height="256"></canvas>
</body>

</html>