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<!--
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.
-->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<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 id="vshader" type="x-shader/x-vertex">
attribute vec3 pos;
void main()
{
gl_Position = vec4(pos, 1);
}
</script>
<script id="fshader" type="x-shader/x-fragment">
precision mediump float;
uniform vec4 col;
void main()
{
gl_FragColor = col;
}
</script>
<script>
"use strict";
var wtu = WebGLTestUtils;
function draw(gl, arr, colLoc, col)
{
var vertices = new Float32Array(arr);
var vertBuf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuf);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
gl.vertexAttribPointer(0, 3, gl.FLOAT, false, 0, 0);
gl.uniform4fv(colLoc, col);
gl.drawArrays(gl.TRIANGLE_STRIP, 0, vertices.length / 3);
}
function clear(gl, col, z)
{
gl.clearColor(col[0], col[1], col[2], col[3]);
gl.clearDepth(z);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
}
function check(gl)
{
wtu.checkCanvasRect(gl, 0, 0, 16, 16, [0, 255, 0, 255], 'result should be green');
}
function runTest()
{
var flatSquare = [-1, -1, 0,
-1, 1, 0,
1, -1, 0,
1, 1, 0];
var slantedSquare = [-1, -1, -0.5,
-1, 1, -0.5,
1, -1, 0.5,
1, 1, 0.5];
var red = [1, 0, 0, 1];
var green = [0, 1, 0, 1];
var blue = [0, 0, 1, 1];
var gl = wtu.create3DContext('testbed', { antialias: false });
if (!gl)
{
testFailed('could not create context');
return;
}
var program = wtu.setupProgram(gl, ['vshader', 'fshader'], ['pos']);
var colLoc = gl.getUniformLocation(program, 'col');
gl.enableVertexAttribArray(0);
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
debug('Polygon offset fill should be off by default');
clear(gl, red, 1.0);
draw(gl, slantedSquare, colLoc, blue);
draw(gl, slantedSquare, colLoc, green);
check(gl);
debug('Polygon offset units should have no effect when fill is off');
clear(gl, red, 1.0);
draw(gl, slantedSquare, colLoc, blue);
gl.polygonOffset(0, 10);
draw(gl, slantedSquare, colLoc, green);
check(gl);
debug('Polygon offset factor should have no effect when fill is off');
clear(gl, red, 1.0);
gl.polygonOffset(0, 0);
draw(gl, slantedSquare, colLoc, blue);
gl.polygonOffset(1.0, 0);
draw(gl, slantedSquare, colLoc, green);
check(gl);
debug('Zero polygon offset units and factor should have no effect');
clear(gl, red, 1.0);
gl.enable(gl.POLYGON_OFFSET_FILL);
gl.polygonOffset(0, 0);
draw(gl, slantedSquare, colLoc, blue);
draw(gl, slantedSquare, colLoc, green);
check(gl);
// It appears to be VERY common for drivers to implement the units offset in
// floating-point arithmetic, which results in rount-to-nearest-even to cause
// an offset of 1 to sometimes not alter the order between these polygons.
debug('Polygon offset units of 2 should alter order of flat polygons');
clear(gl, red, 1.0);
draw(gl, flatSquare, colLoc, green);
gl.polygonOffset(0, 2);
draw(gl, flatSquare, colLoc, blue);
check(gl);
debug('Polygon offset factor of 0.1 should alter order of slanted polygons');
clear(gl, red, 1.0);
gl.polygonOffset(0, 0);
draw(gl, slantedSquare, colLoc, green);
gl.polygonOffset(0.1, 0);
draw(gl, slantedSquare, colLoc, blue);
check(gl);
debug('Polygon offset factor of 0.1 should not alter order of flat polygons');
clear(gl, red, 1.0);
gl.polygonOffset(0, 0);
draw(gl, flatSquare, colLoc, blue);
gl.polygonOffset(0.1, 0);
draw(gl, flatSquare, colLoc, green);
check(gl);
debug('Disabling polygon offset fill should leave order unaffected');
clear(gl, red, 1.0);
gl.polygonOffset(0.1, 1);
gl.disable(gl.POLYGON_OFFSET_FILL);
draw(gl, slantedSquare, colLoc, blue);
draw(gl, slantedSquare, colLoc, green);
check(gl);
debug('Enabling polygon offset fill should affect order again');
clear(gl, red, 1.0);
draw(gl, slantedSquare, colLoc, green);
gl.enable(gl.POLYGON_OFFSET_FILL);
draw(gl, slantedSquare, colLoc, blue);
check(gl);
}
</script>
</head>
<body>
<canvas id="testbed" width="16" height="16" style="width:50px; height:50px"></canvas>
<div id="description"></div>
<div id="console"></div>
<script>
"use strict";
description('Verify that polygon offset works');
runTest();
var successfullyParsed = true;
</script>
<script src="../../js/js-test-post.js"></script>
</body>
</html>