<!--
Copyright (c) 2019 The Khronos Group Inc.
Use of this source code is governed by an MIT-style license that can be
found in the LICENSE.txt file.
-->

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Draw WebGL to Canvas2D Repeatedly</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>
</head>
<body>
<div id="description"></div>
<div id="console"></div>
<canvas id="canvas-webgl" width="256" height="256"></canvas>
<canvas id="canvas-2d" width="256" height="256"></canvas>
<script>
"use strict";
const wtu = WebGLTestUtils;

const sz = 256;

function drawTo2DCanvas(c2, webGLCanvas) {
  // Always clear 2D canvas to solid green first.
  c2.clearRect(0, 0, sz, sz);
  c2.fillStyle = 'rgb(0,255,0)';
  c2.fillRect(0, 0, sz, sz);
  // Draw WebGL canvas to this canvas.
  c2.drawImage(webGLCanvas, 0, 0);
}

function runTest() {
  description();
  debug('Repeatedly drawing a WebGL canvas to a 2D canvas should only draw the most recently rendered WebGL content.');
  debug('Regression test for <a href="http://crbug.com/894021">http://crbug.com/894021</a>');

  let c2 = document.getElementById('canvas-2d').getContext('2d');
  let webGLCanvas = document.getElementById('canvas-webgl');
  let gl = wtu.create3DContext(webGLCanvas, { alpha: true, antialias: false, premultipliedAlpha: true });
  let tolerance = 2;

  // Clear left half of WebGL canvas to red and right half to
  // transparent black.
  gl.disable(gl.SCISSOR_TEST);
  gl.clearColor(0.0, 0.0, 0.0, 0.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.scissor(0, 0, sz / 2, sz);
  gl.enable(gl.SCISSOR_TEST);
  gl.clearColor(1.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  // Draw to 2D canvas.
  drawTo2DCanvas(c2, webGLCanvas);

  // Clear right half of WebGL canvas to red and left half to
  // transparent black.
  gl.disable(gl.SCISSOR_TEST);
  gl.clearColor(0.0, 0.0, 0.0, 0.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.scissor(sz / 2, 0, sz / 2, sz);
  gl.enable(gl.SCISSOR_TEST);
  gl.clearColor(1.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  // Draw to 2D canvas.
  drawTo2DCanvas(c2, webGLCanvas);

  // Clear WebGL canvas to transparent black.
  gl.disable(gl.SCISSOR_TEST);
  gl.clearColor(0.0, 0.0, 0.0, 0.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  // Draw to 2D canvas.
  drawTo2DCanvas(c2, webGLCanvas);

  // 2D canvas should be green.
  // In the error case, the rendering results from earlier draws were
  // being accumulated, so the 2D canvas was ultimately red.
  wtu.checkCanvasRect(c2, 0, 0, sz, sz,
                      [ 0, 255, 0, 255 ],
                      "should be green",
                      tolerance);

  finishTest();
}

requestAnimationFrame(runTest);
</script>
</body>
</html>
