<!--
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 vec2 pos;

void main()
{
    gl_Position = vec4(pos, 0, 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, 2, gl.FLOAT, false, 0, 0);
    gl.uniform4fv(colLoc, col);
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, vertices.length / 2);
}

function clear(gl, col) {
    gl.clearColor(col[0], col[1], col[2], col[3]);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
}

function check(gl, winding, shoulddraw) {
    var msg = winding + ' face was ' + (shoulddraw ? '' : 'not ') + 'drawn.';
    wtu.checkCanvasRect(gl, 0, 0, 1, 1, [0, 255, 0, 255], msg);
}

function runTest() {
    var cwVertices = [-1, -1, -1, 1, 1, -1, 1, 1];
    var ccwVertices = [-1, 1, -1, -1, 1, 1, 1, -1];
    var red = [1, 0, 0, 1];
    var green = [0, 1, 0, 1];
    var ok;

    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);

    debug('CULL_FACE should be off by default');
    clear(gl, red);
    draw(gl, ccwVertices, colLoc, green);
    check(gl, 'CCW', true);
    clear(gl, red);
    draw(gl, cwVertices, colLoc, green);
    check(gl, 'CW', true);

    debug('Enabling CULL_FACE');
    gl.enable(gl.CULL_FACE);

    debug('BACK and CCW should be set by default');
    clear(gl, red);
    draw(gl, ccwVertices, colLoc, green);
    check(gl, 'CCW', true);
    clear(gl, green);
    draw(gl, cwVertices, colLoc, red);
    check(gl, 'CW', false);

    var tests = [{ cullFace : 'BACK', frontFace : 'CCW', drawCCW : true, drawCW : false},
                 { cullFace : 'BACK', frontFace : 'CW', drawCCW : false, drawCW : true},
                 { cullFace : 'FRONT', frontFace : 'CCW', drawCCW : false, drawCW : true },
                 { cullFace : 'FRONT', frontFace : 'CW', drawCCW : true, drawCW : false},
                 { cullFace : 'FRONT_AND_BACK', frontFace : 'CCW', drawCCW : false, drawCW : false},
                 { cullFace : 'FRONT_AND_BACK', frontFace : 'CW', drawCCW : false, drawCW : false}];

    for (var i = 0; i < tests.length; ++i) {
        var t = tests[i];
        debug('Setting ' + t.cullFace + ' and ' + t.frontFace);
        gl.cullFace(gl[t.cullFace]);
        gl.frontFace(gl[t.frontFace]);
        clear(gl, t.drawCCW ? red : green);
        draw(gl, ccwVertices, colLoc, t.drawCCW ? green : red);
        check(gl, 'CCW', t.drawCCW);
        clear(gl, t.drawCW ? red : green);
        draw(gl, cwVertices, colLoc, t.drawCW ? green : red);
        check(gl, 'CW', t.drawCW);
    }
}
</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 culling works');
runTest();
var successfullyParsed = true;
</script>
<script src="../../js/js-test-post.js"></script>
</body>
</html>
