加载场景，基本相机操作

<div class="page-header"><h3>10、加载场景，基本相机操作</h3></div>

<canvas id = "test10-canvas" width = "800" height = "600"></canvas>
<div id="loadingtext">正在加载世界……</div>
<br/>
(WSAD控制移动，逗号/句号 控制 上下看)

<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;
    void main(void)
    {
        gl_FragColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
    }
</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 = $("#test10-canvas")[0];
    initGL(canvas);
    initShaders();
    initBuffers();
    initTexture();

    loadWorld();

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

    $(document).keydown(handleKeyDown);
    $(document).keyup(handleKeyUp);
}
function tick()
{
    requestAnimFrame(tick);
    handleKeys();
    drawScene();
    animate();
}
function loadWorld()
{
    $.getJSON(
        "/Public/json/world.json", 
        function(data)
        {
            handleLoadedWorld(data);
        }
    );
}
var worldVertexPositionBuffer = null;
var worldVertexTextureCoordBuffer = null;
function handleLoadedWorld(data)
{
    var vertexCount = 0;
    var vertexPositions = [];
    var vertexTextureCoords = [];

    for(var i = 0; typeof(data[i]) != "undefined"; i ++)
    {
        //环境中一个部分的顶点坐标
        vertexPositions = 
            vertexPositions.concat(data[i].vertexPositions);
        //然后是纹理坐标
        vertexTextureCoords = 
            vertexTextureCoords.concat(data[i].vertexTextureCoords);
        vertexCount ++;
    }
    worldVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, worldVertexPositionBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertexPositions), gl.STATIC_DRAW);
    worldVertexPositionBuffer.itemSize = 3;
    worldVertexPositionBuffer.numItems = data.vertexCount;

    worldVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, worldVertexTextureCoordBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertexTextureCoords), gl.STATIC_DRAW);
    worldVertexTextureCoordBuffer.itemSize = 2;
    worldVertexTextureCoordBuffer.numItems = data.vertexCount;

    $("#loadingtext").text("");
}
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 crackTexture;
function initTexture()
{
    crackTexture = gl.createTexture();
    crackTexture.image = new Image();
    crackTexture.image.onload = function()
    {
        handleLoadedTexture(crackTexture);
        tick();
    }
    crackTexture.image.src = "/Public/image/cracktexture.jpg";
}
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.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");
}


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 pitch = 0;
var pitchRate = 0;

var yaw = 0;
var yawRate = 0;
var xPos = 0;
var yPos = 0.4;
var zPos = 0;

var speed = 0;
function handleKeys()
{
    if(currentlyPressedKeys[188])
    {
        //","/"<"逗号键
        pitchRate = -0.1;
    }
    else if(currentlyPressedKeys[190])
    {
        //"."/">"句号键
        pitchRate = 0.1;
    }
    else
    {
        pitchRate = 0;
    }
    if (currentlyPressedKeys[65])
    {
        //A
        yawRate = 0.1;
    } 
    else if (currentlyPressedKeys[68])
    {
        //D
        yawRate = -0.1;
    }
    else
    {
        yawRate = 0;
    }
    if(currentlyPressedKeys[87])
    {
        //W
        speed = 0.003;
    }
    else if(currentlyPressedKeys[83])
    {
        //S
        speed = -0.003;
    }
    else
    {
        speed = 0;
    }
}
function drawScene()
{
    gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    if(worldVertexTextureCoordBuffer == null || worldVertexPositionBuffer == null)
    {
        return;
    }
    mat4.perspective(pMatrix, 45, 
        gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);

    mat4.identity(mvMatrix);

    mat4.rotate(mvMatrix, mvMatrix, degToRad(-pitch), [1, 0, 0]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(-yaw), [0, 1, 0]);
    mat4.translate(mvMatrix, mvMatrix, [-xPos, -yPos, -zPos]);

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

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

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

    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLES, 0, worldVertexPositionBuffer.numItems);
}

function degToRad(degrees)
{
    return degrees * Math.PI / 180;
}
var lastTime = 0;
var joggingAngle = 0;
function animate()
{
    var timeNow = new Date().getTime();
    if(lastTime != 0)
    {
        var elapsed = timeNow - lastTime;
        if(speed != 0)
        {
            xPos -= Math.sin(degToRad(yaw)) * speed * elapsed;
            zPos -= Math.cos(degToRad(yaw)) * speed * elapsed;
            joggingAngle += elapsed * 0.6;
            yPos = Math.sin(degToRad(joggingAngle)) / 20 + 0.4;
        }
        yaw += yawRate * elapsed;
        pitch += pitchRate * elapsed;
    }
    lastTime = timeNow;
}
</script>