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<!-- author: Bill Baxter (wbaxter at google.com) -->

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Floored Division Accuracy Bug</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>
<canvas id="repro" style="border: none;" width="256" height="256"></canvas>
<div id="description"></div>
<div id="console"></div>

<script id="shader-vs" type="x-shader/x-vertex">
attribute vec2 pos;
uniform float divisor;
varying vec4 vColor;
void main(void) {
  gl_Position = vec4(pos, 0.0, 1.0);
  float index = 9.0;
  // Floating point operations don't have any guaranteed precision, but they
  // should at least be accurate to 1 part in 10^5.
  float value = floor((index / divisor) * 1.00001);
  vColor = (value == 3.) ? vec4(0, 1, 0, 1) : vec4(1, 0, 0, 1);
}
</script>

<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
varying vec4 vColor;
void main(void) {
  gl_FragColor = vColor;
}
</script>
<script>
"use strict";

description();
debug("");
// Reproduces bug seen on Mac OS X with AMD Radeon HD 6490 GPU
debug("If things are working correctly, then the square will be green.");
debug("If your card thinks floor(9. / 3.) is not 3 to within 1 part in 10^5, ");
debug("then the square will be red.");

var wtu = WebGLTestUtils;
var canvas = document.getElementById("repro");
var gl = wtu.create3DContext(canvas);
if (!gl) {
  testFailed("context does not exist");
} else {
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
  wtu.setupUnitQuad(gl);
  var program = wtu.setupProgram(gl, ["shader-vs", "shader-fs"], ["pos"], undefined, true);
  gl.uniform1f(gl.getUniformLocation(program, "divisor"), 3);
  wtu.drawUnitQuad(gl);
  wtu.checkCanvasRect(gl, 128, 128, 128, 128, [ 0, 255, 0, 255 ], "should be green", 1);
}

var successfullyParsed = true;
</script>
<script src="../../../js/js-test-post.js"></script>
</body>
</html>
