优化代码结构，多物体运动

<div class="page-header"><h3>9、优化代码结构，多物体运动</h3></div>

<canvas id = "test09-canvas" width = "800" height = "600"></canvas>

<br/>
<input type="checkbox" id="twinkle" /> 发亮
<br/>
(逗号/句号 控制 靠近/远离，W/S 控制旋转)

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

    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;
    varying vec2 vTextureCoord;

    void main(void)
    {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
        vTextureCoord = aTextureCoord;
    }
</script>

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

    uniform sampler2D uSampler;

    uniform vec3 uColor;

    void main(void)
    {
        vec4 textureColor = 
            texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
        gl_FragColor = 
            textureColor * vec4(uColor, 1.0);
    }
</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 = $("#test09-canvas")[0];
    initGL(canvas);
    initShaders();
    initBuffers();
    initTexture();

    initWorldObjects();

    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    $(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 starTexture;
function initTexture()
{
    starTexture = gl.createTexture();
    starTexture.image = new Image();
    starTexture.image.onload = function()
    {
        handleLoadedTexture(starTexture);
        tick();
    }
    starTexture.image.src = "/Public/image/star.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);

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

    shaderProgram.pMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mvMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uMVMatrix");
    shaderProgram.samplerUniform = 
        gl.getUniformLocation(shaderProgram, "uSampler");
    shaderProgram.colorUniform = 
        gl.getUniformLocation(shaderProgram, "uColor");

}


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 starVertexPositionBuffer;
var starVertexTextureCoordBuffer;

function initBuffers()
{
    starVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, starVertexPositionBuffer);
    vertices = [
        -1.0, -1.0,  0.0,
         1.0, -1.0,  0.0,
        -1.0,  1.0,  0.0,
         1.0,  1.0,  0.0
        ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), 
        gl.STATIC_DRAW);
    starVertexPositionBuffer.itemSize = 3;
    starVertexPositionBuffer.numItems = 4;

    starVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, starVertexTextureCoordBuffer);
    var textureCoords = [
        0.0, 0.0,
        1.0, 0.0,
        0.0, 1.0,
        1.0, 1.0
        ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), 
        gl.STATIC_DRAW);
    starVertexTextureCoordBuffer.itemSize = 2;
    starVertexTextureCoordBuffer.numItems = 4;
}


var currentlyPressedKeys = {};
function handleKeyDown(event)
{
    currentlyPressedKeys[event.keyCode] = true;
}
function handleKeyUp(event)
{
    currentlyPressedKeys[event.keyCode] = false;
}

var zoom  = -15;
var tilt = 90;
var spin = 90;
function handleKeys()
{
    if(currentlyPressedKeys[190])
    {
        //"."/">"句号键
        zoom -= 0.1;
    }
    if(currentlyPressedKeys[188])
    {
        //","/"<"逗号键
        zoom += 0.1;
    }
    if(currentlyPressedKeys[87])
    {
        //W
        tilt += 2;
    }
    if(currentlyPressedKeys[83])
    {
        //S
        tilt -= 2;
    }    
}
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);

    gl.blendFunc(gl.SRC_ALPHA, gl.ONE);
    gl.enable(gl.BLEND);

    mat4.identity(mvMatrix);

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

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

    var twinkle = $("#twinkle").is(":checked");
    for(var i in stars)
    {
        stars[i].draw(tilt, spin, twinkle);
        spin += 0.1;
    }
}
var stars = [];
function initWorldObjects()
{
    var numStars = 50;
    for(var i = 0; i < numStars; i ++)
    {
        stars.push(new Star((i / numStars) * 5.0, i / numStars));
    }
}
//==========
//Star类
function Star(startingDistance, rotationSpeed)
{
    this.angle = 0;
    this.dist = startingDistance;
    this.rotationSpeed = rotationSpeed;
    //设置一个起始颜色
    this.randomiseColors();
}
Star.prototype.draw = function(tilt, spin, twinkle)
{
    mvPushMatrix();
    //移动到位
    mat4.rotate(mvMatrix, mvMatrix, degToRad(this.angle), [0.0, 1.0, 0.0]);
    mat4.translate(mvMatrix, mvMatrix, [this.dist, 0.0, 0.0]);
    //旋转
    mat4.rotate(mvMatrix, mvMatrix, degToRad(-this.angle), [0.0, 1.0, 0.0]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(-tilt), [1.0, 0.0, 0.0]);
    if(twinkle)
    {
        //画一个不旋转的star
        gl.uniform3f(shaderProgram.colorUniform, 
            this.twinkleR, this.twinkleG, this.twinkleB);
        drawStar();
    }
    //所有Star围绕Z旋转
    mat4.rotate(mvMatrix, mvMatrix, degToRad(spin), [0.0, 0.0, 1.0]);
    //画颜色
    gl.uniform3f(shaderProgram.colorUniform, this.r, this.g, this.b);
    drawStar();
    mvPopMatrix();
};

var effectiveFPMS = 60 / 1000;
Star.prototype.animate = function(elapsedTime)
{
    this.angle += this.rotationSpeed * effectiveFPMS * elapsedTime;
    //逐步减小与中心的距离
    this.dist -= 0.01 * effectiveFPMS * elapsedTime;
    if(this.dist < 0.0)
    {
        this.dist += 5.0;
        this.randomiseColors();
    }
};

Star.prototype.randomiseColors = function()
{
    //给星星一个随机的颜色
    this.r = Math.random();
    this.g = Math.random();
    this.b = Math.random();
    //如果打开了发亮开关，则多绘制一次，用另一个随机的颜色作为亮光
    this.twinkleR = Math.random();
    this.twinkleG = Math.random();
    this.twinkleB = Math.random();
};
//==========

function drawStar()
{
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, starTexture);
    gl.uniform1i(shaderProgram.samplerUniform, 0);

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

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

    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, starVertexPositionBuffer.numItems);
}

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;

        for(var i in stars)
        {
            stars[i].animate(elapsed);
        }
    }
    lastTime = timeNow;
}
</script>