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<!--
/*
** Copyright (c) 2013 The Khronos Group Inc.
**
** Permission is hereby granted, free of charge, to any person obtaining a
** copy of this software and/or associated documentation files (the
** "Materials"), to deal in the Materials without restriction, including
** without limitation the rights to use, copy, modify, merge, publish,
** distribute, sublicense, and/or sell copies of the Materials, and to
** permit persons to whom the Materials are furnished to do so, subject to
** the following conditions:
**
** The above copyright notice and this permission notice shall be included
** in all copies or substantial portions of the Materials.
**
** THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
** MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
*/
-->
<!-- 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>
</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;
// 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.");
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>
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