<!--
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.
-->

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

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Modulo Arithmetic 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>
<script src="../../../js/glsl-conformance-test.js"></script>
</head>

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

<script id="shader-vs" type="x-shader/x-vertex">
attribute vec4 vPosition;
uniform float divisor;
varying vec4 vColor;
void main(void) {
  gl_Position = vPosition;
  float index = 9.0;
  // mod(x, y) is computed as x-y*floor(x/y).  There are no guarantees on
  // the precision of floating point operations in WebGL shaders, but division
  // should be accurate to at least 1 part in 10^5.
  float value = mod(index * 1.00001, divisor);
  vColor = (value < 1.) ? 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 mod(9,3) is not 0, then the square will be red.");

GLSLConformanceTester.runRenderTests([
{
  vShaderId: 'shader-vs',
  vShaderSuccess: true,
  fShaderId: 'shader-fs',
  fShaderSuccess: true,
  linkSuccess: true,
  passMsg: 'Test that mod(9/3) is 0',
  uniforms: [{name: "divisor", functionName: "uniform1f", value: 3}]
}
]);
</script>
</body>
</html>
