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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Bug - the precision qualifier of a constant variable should affect the precision of a consuming operation</title>
<link rel="stylesheet" href="../../../resources/js-test-style.css"/>
<script src="../../../resources/js-test-pre.js"></script>
<script src="../../resources/webgl-test-utils.js"></script>
</head>
<body>
<canvas id="canvas" width="256" height="256"> </canvas>
<div id="description"></div>
<div id="console"></div>
<script id="vshader" type="x-shader/x-vertex">
attribute vec3 aPosition;

void main() {
    gl_Position = vec4(aPosition, 1);
}
</script>
<script id="fshader" type="x-shader/x-fragment">
// It is assumed that uTest is set to 0. It's here to make the expression not constant.
uniform mediump float uTest;

void main() {
    // exact representation of 4096.5 requires 13 bits of relative precision.
    const highp float c = 4096.5;
    mediump float a = 0.0;
    // Below, addition should be evaluated at highp, since one of the operands has the highp qualifier.
    // Thus fract should also be evaluated at highp.
    // See OpenGL ES Shading Language spec section 4.5.2.
    // This should make the result 0.5, since highp provides at least 16 bits of relative precision.
    // (exceptions for operation precision are allowed for a small number of computationally
    // intensive built-in functions, but it is reasonable to think that fract is not one of those).
    // However, if fract() is incorrectly evaluated at minimum precision fulfilling mediump criteria,
    // or at IEEE half float precision, the result is 0.0.
    a = fract(c + uTest);

    // Multiply by 2.0 to make the color green.
    gl_FragColor = vec4(0.0, 2.0 * a, 0.0, 1.0);
}
</script>
<script type="text/javascript">
"use strict";
description();
var wtu = WebGLTestUtils;

function test() {
  var gl = wtu.create3DContext("canvas");
  if (!gl) {
    testFailed("context does not exist");
    return;
  }
  if (gl.getShaderPrecisionFormat(gl.FRAGMENT_SHADER, gl.HIGH_FLOAT).precision == 0) {
    testPassed("highp precision not supported");
  } else {
    wtu.setupUnitQuad(gl);
    var program = wtu.setupProgram(gl, ["vshader", "fshader"], ["aPosition"], undefined, true);
    var uniformLoc = gl.getUniformLocation(program, 'uTest');
    gl.uniform1f(uniformLoc, 0);
    wtu.drawUnitQuad(gl);
    wtu.checkCanvasRect(gl, 0, 0, 256, 256, [0, 255, 0, 255]);
  }
};

test();
var successfullyParsed = true;
finishTest();
</script>
</body>
</html>

