﻿<!--
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>
