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28 <!-- author: Bill Baxter (wbaxter at google.com) -->
33 <meta charset="utf-8">
34 <title>Floored Division Accuracy Bug</title>
35 <link rel="stylesheet" href="../../../resources/js-test-style.css"/>
36 <script src="../../../resources/js-test-pre.js"></script>
37 <script src="../../resources/webgl-test-utils.js"></script>
41 <canvas id="repro" style="border: none;" width="256" height="256"></canvas>
42 <div id="description"></div>
43 <div id="console"></div>
45 <script id="shader-vs" type="x-shader/x-vertex">
47 uniform float divisor;
50 gl_Position = vec4(pos, 0.0, 1.0);
52 // Floating point operations don't have any guaranteed precision, but they
53 // should at least be accurate to 1 part in 10^5.
54 float value = floor((index / divisor) * 1.00001);
55 vColor = (value == 3.) ? vec4(0, 1, 0, 1) : vec4(1, 0, 0, 1);
59 <script id="shader-fs" type="x-shader/x-fragment">
60 precision mediump float;
63 gl_FragColor = vColor;
69 // Reproduces bug seen on Mac OS X with AMD Radeon HD 6490 GPU
70 debug("If things are working correctly, then the square will be green.");
71 debug("If your card thinks floor(9. / 3.) is not 3 to within 1 part in 10^5, ");
72 debug("then the square will be red.");
74 var wtu = WebGLTestUtils;
75 var canvas = document.getElementById("repro");
76 var gl = wtu.create3DContext(canvas);
78 testFailed("context does not exist");
81 gl.clearColor(0.0, 0.0, 0.0, 1.0);
82 gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
83 wtu.setupUnitQuad(gl);
84 var program = wtu.setupProgram(gl, ["shader-vs", "shader-fs"], ["pos"]);
85 gl.uniform1f(gl.getUniformLocation(program, "divisor"), 3);
87 wtu.checkCanvasRect(gl, 128, 128, 128, 128, [ 0, 255, 0, 255 ], "should be green", 1);
88 var successfullyParsed = true;
90 <script src="../../../resources/js-test-post.js"></script>