深度缓冲，透明度与混合

<div class="page-header"><h3>8、深度缓冲，透明度与混合</h3></div>

<canvas id = "test08-canvas" width = "800" height = "600"></canvas>
<br/>
<input type="checkbox" id="blending" checked /> 使用混合
<br/>
不透明度（Alpha）级别 <input type="text" id="alpha" value="0.5" /><br/>
<br/>
<input type="checkbox" id="lighting" checked /> 使用光照
<br/>
(逗号/句号 控制 靠近/远离，WSAD键控制四个方向旋转速度)
<br/>
<h4>方向光:</h4>
<table>
    <tr>
        <td><b>方向:</b></td>
        <td>X: <input type="text" id="lightDirectionX" value="-0.25" /></td>
        <td>Y: <input type="text" id="lightDirectionY" value="-0.25" /></td>
        <td>Z: <input type="text" id="lightDirectionZ" value="-1.0" /></td>
    </tr>
    <tr>
        <td><b>颜色:</b></td>
        <td>R: <input type="text" id="directionalR" value="0.8" /></td>
        <td>G: <input type="text" id="directionalG" value="0.8" /></td>
        <td>B: <input type="text" id="directionalB" value="0.8" /></td>
    </tr>
</table>
<h4>环境光:</h4>
<table style="border: 0; padding: 10px;">
    <tr>
        <td><b>颜色:</b></td>
        <td>R: <input type="text" id="ambientR" value="0.2" /></td>
        <td>G: <input type="text" id="ambientG" value="0.2" /></td>
        <td>B: <input type="text" id="ambientB" value="0.2" /></td>
    </tr>
</table>

<script id = "shader-vs" type = "x-shader/x-vertex">
    attribute vec3 aVertexPosition;
    attribute vec3 aVertexNormal;
    attribute vec2 aTextureCoord;

    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;
    uniform mat3 uNMatrix;

    uniform vec3 uAmbientColor;

    uniform vec3 uLightingDirection;
    uniform vec3 uDirectionalColor;

    uniform bool uUseLighting;

    varying vec2 vTextureCoord;
    varying vec3 vLightWeighting;

    void main(void)
    {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
        vTextureCoord = aTextureCoord;

        if(!uUseLighting)
        {
            vLightWeighting = vec3(1.0, 1.0, 1.0);
        }
        else
        {
            vec3 transformedNormal = uNMatrix * aVertexNormal;
            float directionalLightWeighting = 
                max(dot(transformedNormal, uLightingDirection), 0.0);
            vLightWeighting = 
                uAmbientColor + uDirectionalColor * directionalLightWeighting;
        }
    }
</script>

<script id = "shader-fs" type = "x-shader/x-fragment">
    precision mediump float;
    varying vec2 vTextureCoord;
    varying vec3 vLightWeighting;

    uniform float uAlpha;

    uniform sampler2D uSampler;
    void main(void)
    {
        vec4 textureColor = 
            texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
        gl_FragColor = 
            vec4(textureColor.rgb * vLightWeighting, textureColor.a * uAlpha);
    }
</script>
<script type="text/javascript">
    requestAnimFrame = window.requestAnimationFrame || 
        window.mozRequestAnimationFrame || 
        window.webkitRequestAnimationFrame || 
        window.msRequestAnimationFrame || 
        window.oRequestAnimationFrame || 
        function(callback) { setTimeout(callback, 1000 / 60); }; 
</script>
<script type="text/javascript">

$(document).ready(function ()
{
    webGLStart();
});

function webGLStart()
{
    var canvas = $("#test08-canvas")[0];
    initGL(canvas);
    initShaders();
    initBuffers();
    initTexture();

    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    gl.enable(gl.DEPTH_TEST);
//  gl.depthFunc(gl.LESS);
//    setTimeout("tick()", 100);

    $(document).keydown(handleKeyDown);
    $(document).keyup(handleKeyUp);
}
function tick()
{
    requestAnimFrame(tick);
    handleKeys();
    drawScene();
    animate();
}

var gl;
function initGL(canvas)
{
    try
    {
        gl = canvas.getContext("webgl") || canvas.getContext("experimental-webgl");
        gl.viewportWidth = canvas.width;
        gl.viewportHeight = canvas.height;
    }catch(e){}
    if(!gl)
    {
        alert("无法初始化“WebGL”。");
    }
}

var crateTexture;
function initTexture()
{
    crateTexture = gl.createTexture();
    crateTexture.image = new Image();
    crateTexture.image.onload = function()
    {
        handleLoadedTexture(crateTexture);
        tick();
    }
    crateTexture.image.src = "/Public/image/glass.gif";
}
function handleLoadedTexture(texture)
{
    gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, 1);


    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, 
        gl.UNSIGNED_BYTE, texture.image);
    gl.texParameteri(gl.TEXTURE_2D, 
        gl.TEXTURE_MAG_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, 
        gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);

    gl.generateMipmap(gl.TEXTURE_2D);

    gl.bindTexture(gl.TEXTURE_2D, null);
}
function getShader(gl, id)
{
    var shaderScript = $("#" + id);
    if(!shaderScript.length)
    {
        return null;
    }
    var str = shaderScript.text();

    var shader;
    if(shaderScript[0].type == "x-shader/x-fragment")
    {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    }
    else if(shaderScript[0].type == "x-shader/x-vertex")
    {
        shader = gl.createShader(gl.VERTEX_SHADER);
    }
    else
    {
        return null;
    }
    gl.shaderSource(shader, str);
    gl.compileShader(shader);
    if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS))
    {
        alert(gl.getShaderInfoLog(shader));
        return null;
    }
    return shader;
}

var shaderProgram;
function initShaders()
{
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");

    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);

    if(!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS))
    {
        alert("无法初始化“Shader”。");
    }
    gl.useProgram(shaderProgram);

    shaderProgram.vertexPositionAttribute = 
        gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

    shaderProgram.vertexNormalAttribute = 
        gl.getAttribLocation(shaderProgram, "aVertexNormal");
    gl.enableVertexAttribArray(shaderProgram.vertexNormalAttribute);

    shaderProgram.textureCoordAttribute = 
        gl.getAttribLocation(shaderProgram, "aTextureCoord");
    gl.enableVertexAttribArray(shaderProgram.textureCoordAttribute);

    shaderProgram.pMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mvMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uMVMatrix");
    shaderProgram.nMatrixUniform  = 
        gl.getUniformLocation(shaderProgram, "uNMatrix");
    shaderProgram.samplerUniform = 
        gl.getUniformLocation(shaderProgram, "uSampler");
    shaderProgram.useLightingUniform = 
        gl.getUniformLocation(shaderProgram, "uUseLighting");
    shaderProgram.ambientColorUniform = 
        gl.getUniformLocation(shaderProgram, "uAmbientColor");
    shaderProgram.lightingDirectionUniform = 
        gl.getUniformLocation(shaderProgram, "uLightingDirection");
    shaderProgram.directionalColorUniform = 
        gl.getUniformLocation(shaderProgram, "uDirectionalColor");
    shaderProgram.alphaUniform = 
        gl.getUniformLocation(shaderProgram, "uAlpha");
}


var mvMatrix = mat4.create();

var mvMatrixStack = [];

var pMatrix = mat4.create();

function mvPushMatrix()
{
    var copy = mat4.clone(mvMatrix);
    mvMatrixStack.push(copy);
}
function mvPopMatrix()
{
    if(mvMatrixStack.length == 0)
    {
        throw "不合法的矩阵出栈操作!";
    }
    mvMatrix = mvMatrixStack.pop();
}

function setMatrixUniforms()
{
    gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
    gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);


    var normalMatrix = mat3.create();

    mat3.fromMat4(normalMatrix, mvMatrix);
    mat3.invert(normalMatrix, normalMatrix);
    mat3.transpose(normalMatrix, normalMatrix);

    gl.uniformMatrix3fv(shaderProgram.nMatrixUniform, false, normalMatrix);
}


var cubeVertexPositionBUffer;
var cubeVertexTextureCoordBuffer;
var cubeVertexIndexBuffer;
var cubeVertexNormalBuffer;

function initBuffers()
{
    cubeVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
    vertices = [
                // 正面
                -1.0, -1.0,  1.0,
                 1.0, -1.0,  1.0,
                 1.0,  1.0,  1.0,
                -1.0,  1.0,  1.0,

                // 背面
                -1.0, -1.0, -1.0,
                -1.0,  1.0, -1.0,
                 1.0,  1.0, -1.0,
                 1.0, -1.0, -1.0,

                // 顶部
                -1.0,  1.0, -1.0,
                -1.0,  1.0,  1.0,
                 1.0,  1.0,  1.0,
                 1.0,  1.0, -1.0,

                // 底部
                -1.0, -1.0, -1.0,
                 1.0, -1.0, -1.0,
                 1.0, -1.0,  1.0,
                -1.0, -1.0,  1.0,

                // 右侧面
                 1.0, -1.0, -1.0,
                 1.0,  1.0, -1.0,
                 1.0,  1.0,  1.0,
                 1.0, -1.0,  1.0,

                // 左侧面
                -1.0, -1.0, -1.0,
                -1.0, -1.0,  1.0,
                -1.0,  1.0,  1.0,
                -1.0,  1.0, -1.0,
                ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), 
        gl.STATIC_DRAW);
    cubeVertexPositionBuffer.itemSize = 3;
    cubeVertexPositionBuffer.numItems = 24;

    cubeVertexNormalBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexNormalBuffer);
    var vertexNormals = [
                      // 正面
                        0.0,  0.0,  1.0,
                        0.0,  0.0,  1.0,
                        0.0,  0.0,  1.0,
                        0.0,  0.0,  1.0,

                      // 背面
                        0.0,  0.0, -1.0,
                        0.0,  0.0, -1.0,
                        0.0,  0.0, -1.0,
                        0.0,  0.0, -1.0,

                      // 顶部
                        0.0,  1.0,  0.0,
                        0.0,  1.0,  0.0,
                        0.0,  1.0,  0.0,
                        0.0,  1.0,  0.0,

                      // 底部
                        0.0, -1.0,  0.0,
                        0.0, -1.0,  0.0,
                        0.0, -1.0,  0.0,
                        0.0, -1.0,  0.0,

                      // 右侧面
                        1.0,  0.0,  0.0,
                        1.0,  0.0,  0.0,
                        1.0,  0.0,  0.0,
                        1.0,  0.0,  0.0,

                      // 左侧面
                      -1.0,  0.0,  0.0,
                      -1.0,  0.0,  0.0,
                      -1.0,  0.0,  0.0,
                      -1.0,  0.0,  0.0,
                    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertexNormals), gl.STATIC_DRAW);
    cubeVertexNormalBuffer.itemSize = 3;
    cubeVertexNormalBuffer.numItems = 24;

    cubeVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexTextureCoordBuffer);
    textureCoords = [
                     // 正面
                     0.0, 0.0,
                     1.0, 0.0,
                     1.0, 1.0,
                     0.0, 1.0,

                     // 背面
                     1.0, 0.0,
                     1.0, 1.0,
                     0.0, 1.0,
                     0.0, 0.0,

                     // 顶部
                     0.0, 1.0,
                     0.0, 0.0,
                     1.0, 0.0,
                     1.0, 1.0,

                     // 底部
                     1.0, 1.0,
                     0.0, 1.0,
                     0.0, 0.0,
                     1.0, 0.0,

                     // 右侧面
                     1.0, 0.0,
                     1.0, 1.0,
                     0.0, 1.0,
                     0.0, 0.0,

                     // 左侧面
                     0.0, 0.0,
                     1.0, 0.0,
                     1.0, 1.0,
                     0.0, 1.0,
                    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), 
        gl.STATIC_DRAW);
    cubeVertexTextureCoordBuffer.itemSize = 2;
    cubeVertexTextureCoordBuffer.numItems = 24;

    cubeVertexIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
    var cubeVertexIndices = 
        [
          0, 1, 2,        0, 2, 3,    // 正面
          4, 5, 6,        4, 6, 7,    // 背面
          8, 9, 10,        8, 10, 11,  // 顶部
          12, 13, 14,    12, 14, 15, // 底部
          16, 17, 18,    16, 18, 19, // 右侧面
          20, 21, 22,    20, 22, 23  // 左侧面
        ];
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, 
        new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
    cubeVertexIndexBuffer.itemSize = 1;
    cubeVertexIndexBuffer.numItems = 36;


}

var xRot = 0;
var xSpeed = 3;

var yRot = 0;
var ySpeed = -3;

var z = -5.0;

var filter = 0;

var currentlyPressedKeys = {};
function handleKeyDown(event)
{
    currentlyPressedKeys[event.keyCode] = true;
    if(String.fromCharCode(event.keyCode) == "F")
    {
        filter += 1;
        if(filter == 3)
        {
            filter = 0;
        }
    }
}
function handleKeyUp(event)
{
    currentlyPressedKeys[event.keyCode] = false;
}
function handleKeys()
{
    if(currentlyPressedKeys[190])
    {
        //"."/">"句号键
        z -= 0.05;
    }
    if(currentlyPressedKeys[188])
    {
        //","/"<"逗号键
        z += 0.05;
    }
    if(currentlyPressedKeys[65])
    {
        //A
        ySpeed -= 1;
    }
    if(currentlyPressedKeys[68])
    {
        //D
        ySpeed += 1;
    }
    if(currentlyPressedKeys[87])
    {
        //W
        xSpeed -= 1;
    }
    if(currentlyPressedKeys[83])
    {
        //S
        xSpeed += 1;
    }    
}
function drawScene()
{
    gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    mat4.perspective(pMatrix, 45, 
        gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);

    mat4.identity(mvMatrix);

    mat4.translate(mvMatrix, mvMatrix, [0.0, 0.0, z]);

    mat4.rotate(mvMatrix, mvMatrix, degToRad(xRot), [1, 0, 0]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(yRot), [0, 1, 0]);

    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 
        cubeVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexNormalBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexNormalAttribute, 
        cubeVertexNormalBuffer.itemSize, gl.FLOAT, false, 0, 0);

    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexTextureCoordBuffer);
    gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, 
        cubeVertexTextureCoordBuffer.itemSize, gl.FLOAT, false, 0, 0);

    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, crateTexture);
    gl.uniform1i(shaderProgram.samplerUniform, 0);

    var blending = $("#blending").is(":checked");
    if(blending)
    {
        gl.blendFunc(gl.SRC_ALPHA, gl.ONE);
        gl.enable(gl.BLEND);
        gl.disable(gl.DEPTH_TEST);
        gl.uniform1f(shaderProgram.alphaUniform, parseFloat($("#alpha").val()));
    }
    else
    {
        gl.disable(gl.BLEND);
        gl.enable(gl.DEPTH_TEST);
        gl.uniform1f(shaderProgram.alphaUniform, 1);
    }

    var lighting = $("#lighting").is(":checked");
    gl.uniform1i(shaderProgram.useLightingUniform, lighting);
    if(lighting)
    {
        gl.uniform3f(
            shaderProgram.ambientColorUniform, 
            parseFloat($("#ambientR").val()),
            parseFloat($("#ambientG").val()),
            parseFloat($("#ambientB").val())
            );
        var lightingDirection = [
            parseFloat($("#lightDirectionX").val()),
            parseFloat($("#lightDirectionY").val()),
            parseFloat($("#lightDirectionZ").val())
            ];
        var adjustedLD = vec3.create();
        vec3.normalize(adjustedLD, lightingDirection);
        vec3.scale(adjustedLD, adjustedLD, -1);
        gl.uniform3fv(shaderProgram.lightingDirectionUniform, adjustedLD);
        gl.uniform3f(
            shaderProgram.directionalColorUniform,
            parseFloat($("#directionalR").val()),
            parseFloat($("#directionalG").val()),
            parseFloat($("#directionalB").val())
            );
    }
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
    setMatrixUniforms();
    gl.drawElements(gl.TRIANGLES, 
        cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
}
function degToRad(degrees)
{
    return degrees * Math.PI / 180;
}
var lastTime = 0;
function animate()
{
    var timeNow = new Date().getTime();
    if(lastTime != 0)
    {
        var elapsed = timeNow - lastTime;

        xRot += (xSpeed * elapsed) / 1000.0;
        yRot += (ySpeed * elapsed) / 1000.0;
    }
    lastTime = timeNow;
}
</script>