渲染到纹理

<div class="page-header"><h3>16、渲染到纹理</h3></div>

<canvas id = "test16-canvas" width = "800" height = "600"></canvas>
<br/>
笔记本模型来自： 
<a href="http://www.turbosquid.com/3d-models/apple-macbook-max-free/391534">
    this 3DS Max model by Xedium
</a>
<br/>
月球表面纹理图片来自：
<a href="http://maps.jpl.nasa.gov/">the Jet Propulsion Laboratory</a>.
<br/>

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

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

    varying vec2 vTextureCoord;
    varying vec3 vTransformedNormal;
    varying vec4 vPosition;


    void main(void)
    {
        vPosition = uMVMatrix * vec4(aVertexPosition, 1.0);
        gl_Position = uPMatrix * vPosition;
        vTextureCoord = aTextureCoord;
        vTransformedNormal = uNMatrix * aVertexNormal;
    }
</script>
<script id = "per-fragment-lighting-fs" type = "x-shader/x-fragment">
    precision mediump float;

    varying vec2 vTextureCoord;
    varying vec3 vTransformedNormal;
    varying vec4 vPosition;

    uniform vec3 uMaterialAmbientColor;
    uniform vec3 uMaterialDiffuseColor;
    uniform vec3 uMaterialSpecularColor;
    uniform float uMaterialShininess;
    uniform vec3 uMaterialEmissiveColor;

    uniform bool uShowSpecularHighlights;
    uniform bool uUseTextures;

    uniform vec3 uAmbientLightingColor;

    uniform vec3 uPointLightingLocation;
    uniform vec3 uPointLightingDiffuseColor;
    uniform vec3 uPointLightingSpecularColor;

    uniform sampler2D uSampler;


    void main(void)
    {
        vec3 ambientLightWeighting = uAmbientLightingColor;

        vec3 lightDirection = normalize(uPointLightingLocation - vPosition.xyz);
        vec3 normal = normalize(vTransformedNormal);

        vec3 specularLightWeighting = vec3(0.0, 0.0, 0.0);
        if (uShowSpecularHighlights)
        {
            vec3 eyeDirection = normalize(-vPosition.xyz);
            vec3 reflectionDirection = reflect(-lightDirection, normal);

            float specularLightBrightness = 
                pow(max(dot(reflectionDirection, eyeDirection), 0.0), 
                uMaterialShininess);
            specularLightWeighting = 
                uPointLightingSpecularColor * specularLightBrightness;
        }

        float diffuseLightBrightness = max(dot(normal, lightDirection), 0.0);
        vec3 diffuseLightWeighting = 
            uPointLightingDiffuseColor * diffuseLightBrightness;

        vec3 materialAmbientColor = uMaterialAmbientColor;
        vec3 materialDiffuseColor = uMaterialDiffuseColor;
        vec3 materialSpecularColor = uMaterialSpecularColor;
        vec3 materialEmissiveColor = uMaterialEmissiveColor;
        float alpha = 1.0;
        if (uUseTextures)
        {
            vec4 textureColor = 
                texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
            materialAmbientColor = materialAmbientColor * textureColor.rgb;
            materialDiffuseColor = materialDiffuseColor * textureColor.rgb;
            materialEmissiveColor = materialEmissiveColor * textureColor.rgb;
            alpha = textureColor.a;
        }
        gl_FragColor = vec4(
                           materialAmbientColor * ambientLightWeighting +
                           materialDiffuseColor * diffuseLightWeighting +
                           materialSpecularColor * specularLightWeighting +
                           materialEmissiveColor,
                           alpha
                       );
    }
</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 = $("#test16-canvas");
    initGL(canvas[0]);
    initTextureFramebuffer();
    initShaders();
    initTextures();
    initBuffers();

    loadLaptop();

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

    waitTexture = setInterval("tick()", 100);
}

var textureFlag = [0, 0, 0];
var startTick = false;
var waitTick;
function tick()
{
    if(textureFlag[0] == 1 && textureFlag[1] == 1 && textureFlag[2] == 1)
    {
        startTick = true;
        textureFlag[0] = 2;
        textureFlag[1] = 2;
        textureFlag[2] = 2;
        clearInterval(waitTexture);
    }
    if(startTick)
    {
        requestAnimFrame(tick);
        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 rttFramebuffer;
var rttTexture;
function initTextureFramebuffer()
{
    rttFramebuffer = gl.createFramebuffer();
    gl.bindFramebuffer(gl.FRAMEBUFFER, rttFramebuffer);
    rttFramebuffer.width = 512;
    rttFramebuffer.height = 512;

    rttTexture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, rttTexture);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
    // gl.generateMipmap(gl.TEXTURE_2D);

    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 
        rttFramebuffer.width, rttFramebuffer.height, 
        0, gl.RGBA, gl.UNSIGNED_BYTE, null);

    var renderbuffer = gl.createRenderbuffer();
    gl.bindRenderbuffer(gl.RENDERBUFFER, renderbuffer);
    gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, 
        rttFramebuffer.width, rttFramebuffer.height);

    gl.framebufferTexture2D(
        gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, rttTexture, 0);
    gl.framebufferRenderbuffer(
        gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, renderbuffer);

    gl.bindTexture(gl.TEXTURE_2D, null);
    gl.bindRenderbuffer(gl.RENDERBUFFER, null);
    gl.bindFramebuffer(gl.FRAMEBUFFER, null);
}
var moonTexture;
var crateTexture;
function initTextures()
{
    moonTexture = gl.createTexture();
    moonTexture.image = new Image();
    moonTexture.image.onload = function ()
    {
        handleLoadedTexture(moonTexture)
        textureFlag[0] = 1;
    }
    moonTexture.image.src = "/Public/image/moon.gif";

    crateTexture  = gl.createTexture();
    crateTexture.image = new Image();
    crateTexture.image.onload = function ()
    {
        handleLoadedTexture(crateTexture)
        textureFlag[1] = 1;
    }
    crateTexture.image.src = "/Public/image/crate.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 vertexShader = getShader(gl, "per-fragment-lighting-vs");
    var fragmentShader = getShader(gl, "per-fragment-lighting-fs");

    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.materialAmbientColorUniform =
        gl.getUniformLocation(shaderProgram, "uMaterialAmbientColor");
    shaderProgram.materialDiffuseColorUniform =
        gl.getUniformLocation(shaderProgram, "uMaterialDiffuseColor");
    shaderProgram.materialSpecularColorUniform =
        gl.getUniformLocation(shaderProgram, "uMaterialSpecularColor");
    shaderProgram.materialShininessUniform =
        gl.getUniformLocation(shaderProgram, "uMaterialShininess");
    shaderProgram.materialEmissiveColorUniform =
        gl.getUniformLocation(shaderProgram, "uMaterialEmissiveColor");
    shaderProgram.showSpecularHighlightsUniform =
        gl.getUniformLocation(shaderProgram, "uShowSpecularHighlights");
    shaderProgram.useTexturesUniform =
        gl.getUniformLocation(shaderProgram, "uUseTextures");
    shaderProgram.ambientLightingColorUniform =
        gl.getUniformLocation(shaderProgram, "uAmbientLightingColor");
    shaderProgram.pointLightingLocationUniform =
        gl.getUniformLocation(shaderProgram, "uPointLightingLocation");
    shaderProgram.pointLightingSpecularColorUniform =
        gl.getUniformLocation(shaderProgram, "uPointLightingSpecularColor");
    shaderProgram.pointLightingDiffuseColorUniform =
        gl.getUniformLocation(shaderProgram, "uPointLightingDiffuseColor");
}

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 laptopVertexPositionBuffer;
var laptopVertexNormalBuffer;
var laptopVertexTextureCoordBuffer;
var laptopVertexIndexBuffer;
function loadLaptop() 
{
    $.getJSON(
        "/Public/json/macbook.json", 
        function(data)
        {
            handleLoadedLaptop(data);
            textureFlag[2] = 1;
        }
    );
}
function handleLoadedLaptop(laptopData) 
{
    laptopVertexNormalBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopVertexNormalBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(laptopData.vertexNormals), gl.STATIC_DRAW);
    laptopVertexNormalBuffer.itemSize = 3;
    laptopVertexNormalBuffer.numItems = laptopData.vertexNormals.length / 3;

    laptopVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopVertexTextureCoordBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(laptopData.vertexTextureCoords), gl.STATIC_DRAW);
    laptopVertexTextureCoordBuffer.itemSize = 2;
    laptopVertexTextureCoordBuffer.numItems = 
    laptopData.vertexTextureCoords.length / 2;

    laptopVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopVertexPositionBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(laptopData.vertexPositions), gl.STATIC_DRAW);
    laptopVertexPositionBuffer.itemSize = 3;
    laptopVertexPositionBuffer.numItems = laptopData.vertexPositions.length / 3;

    laptopVertexIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, laptopVertexIndexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, 
        new Uint16Array(laptopData.indices), gl.STREAM_DRAW);
    laptopVertexIndexBuffer.itemSize = 1;
    laptopVertexIndexBuffer.numItems = laptopData.indices.length;
}

var cubeVertexPositionBuffer;
var cubeVertexNormalBuffer;
var cubeVertexTextureCoordBuffer;
var cubeVertexIndexBuffer;

var moonVertexPositionBuffer;
var moonVertexNormalBuffer;
var moonVertexTextureCoordBuffer;
var moonVertexIndexBuffer;

var laptopScreenVertexPositionBuffer;
var laptopScreenVertexNormalBuffer;
var laptopScreenVertexTextureCoordBuffer;

function initBuffers()
{
    //箱子
    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;

    //月亮
    var latitudeBands = 30;
    var longitudeBands = 30;
    var radius = 1;
    var vertexPositionData = [];
    var normalData = [];
    var textureCoordData = [];
    for(var latNumber = 0; latNumber <= latitudeBands; latNumber ++)
    {
        var theta = latNumber * Math.PI / latitudeBands;
        var sinTheta = Math.sin(theta);
        var cosTheta = Math.cos(theta);
        for(var longNumber = 0; longNumber <= longitudeBands; longNumber ++)
        {
            var phi = longNumber * 2 * Math.PI / longitudeBands;
            var sinPhi = Math.sin(phi);
            var cosPhi = Math.cos(phi);
            var x = cosPhi * sinTheta;
            var y = cosTheta;
            var z = sinPhi * sinTheta;
            var u = 1 - (longNumber / longitudeBands);
            var v = 1 - (latNumber / latitudeBands);

            normalData.push(x);
            normalData.push(y);
            normalData.push(z);
            textureCoordData.push(u);
            textureCoordData.push(v);
            vertexPositionData.push(radius * x);
            vertexPositionData.push(radius * y);
            vertexPositionData.push(radius * z);
        }
    }
    var indexData = [];
    for(var latNumber = 0; latNumber < latitudeBands; latNumber ++)
    {
        for(var longNumber = 0; longNumber < longitudeBands; longNumber ++)
        {
            var first = (latNumber * (longitudeBands + 1)) + longNumber;
            var second = first + longitudeBands + 1;
            indexData.push(first);
            indexData.push(second);
            indexData.push(first + 1);
            indexData.push(second);
            indexData.push(second + 1);
            indexData.push(first + 1);
        }
    }
    moonVertexNormalBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, moonVertexNormalBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(normalData), gl.STATIC_DRAW);
    moonVertexNormalBuffer.itemSize = 3;
    moonVertexNormalBuffer.numItems = normalData.length / 3;

    moonVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, moonVertexTextureCoordBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(textureCoordData), gl.STATIC_DRAW);
    moonVertexTextureCoordBuffer.itemSize = 2;
    moonVertexTextureCoordBuffer.numItems = textureCoordData.length / 2;

    moonVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, moonVertexPositionBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertexPositionData), gl.STATIC_DRAW);
    moonVertexPositionBuffer.itemSize = 3;
    moonVertexPositionBuffer.numItems = vertexPositionData.length / 3;

    moonVertexIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, moonVertexIndexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, 
        new Uint16Array(indexData), gl.STATIC_DRAW);
    moonVertexIndexBuffer.itemSize = 1;
    moonVertexIndexBuffer.numItems = indexData.length;

    laptopScreenVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopScreenVertexPositionBuffer);
    vertices = [
         0.580687, 0.659, 0.813106,
        -0.580687, 0.659, 0.813107,
         0.580687, 0.472, 0.113121,
        -0.580687, 0.472, 0.113121,
        ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    laptopScreenVertexPositionBuffer.itemSize = 3;
    laptopScreenVertexPositionBuffer.numItems = 4;

    laptopScreenVertexNormalBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopScreenVertexNormalBuffer);
    var vertexNormals = [
         0.000000, -0.965926, 0.258819,
         0.000000, -0.965926, 0.258819,
         0.000000, -0.965926, 0.258819,
         0.000000, -0.965926, 0.258819,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertexNormals), gl.STATIC_DRAW);
    laptopScreenVertexNormalBuffer.itemSize = 3;
    laptopScreenVertexNormalBuffer.numItems = 4;

    laptopScreenVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, laptopScreenVertexTextureCoordBuffer);
    var textureCoords = [
        1.0, 1.0,
        0.0, 1.0,
        1.0, 0.0,
        0.0, 0.0,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(textureCoords), gl.STATIC_DRAW);
    laptopScreenVertexTextureCoordBuffer.itemSize = 2;
    laptopScreenVertexTextureCoordBuffer.numItems = 4;
}
var laptopScreenAspectRatio = 1.66;

var moonAngle = 180;
var cubeAngle = 0;
function drawSceneOnLaptopScreen()
{
    gl.viewport(0, 0, rttFramebuffer.width, rttFramebuffer.height);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    mat4.perspective(pMatrix, 45, laptopScreenAspectRatio, 0.1, 100.0);

    gl.uniform1i(shaderProgram.showSpecularHighlightsUniform, false);
    gl.uniform3f(shaderProgram.ambientLightingColorUniform, 0.2, 0.2, 0.2);
    gl.uniform3f(shaderProgram.pointLightingLocationUniform, 0, 0, -5);
    gl.uniform3f(shaderProgram.pointLightingDiffuseColorUniform, 0.8, 0.8, 0.8);

    gl.uniform1i(shaderProgram.showSpecularHighlightsUniform, false);
    gl.uniform1i(shaderProgram.useTexturesUniform, true);

    gl.uniform3f(shaderProgram.materialAmbientColorUniform, 1.0, 1.0, 1.0);
    gl.uniform3f(shaderProgram.materialDiffuseColorUniform, 1.0, 1.0, 1.0);
    gl.uniform3f(shaderProgram.materialSpecularColorUniform, 0.0, 0.0, 0.0);
    gl.uniform1f(shaderProgram.materialShininessUniform, 0);
    gl.uniform3f(shaderProgram.materialEmissiveColorUniform, 0.0, 0.0, 0.0);

    mat4.identity(mvMatrix);

    mat4.translate(mvMatrix, mvMatrix, [0, 0, -5]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(30), [1, 0, 0]);

    mvPushMatrix();
    mat4.rotate(mvMatrix, mvMatrix, degToRad(moonAngle), [0, 1, 0]);
    mat4.translate(mvMatrix, mvMatrix, [2, 0, 0]);
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, moonTexture);
    gl.uniform1i(shaderProgram.samplerUniform, 0);

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

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

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

    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, moonVertexIndexBuffer);
    setMatrixUniforms();
    gl.drawElements(gl.TRIANGLES, 
        moonVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
    mvPopMatrix();


    mvPushMatrix();
    mat4.rotate(mvMatrix, mvMatrix, degToRad(cubeAngle), [0, 1, 0]);
    mat4.translate(mvMatrix, mvMatrix, [1.25, 0, 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);

    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
    setMatrixUniforms();
    gl.drawElements(gl.TRIANGLES, 
        cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
    mvPopMatrix();

    gl.bindTexture(gl.TEXTURE_2D, rttTexture);
    gl.generateMipmap(gl.TEXTURE_2D);
    gl.bindTexture(gl.TEXTURE_2D, null);
}
var laptopAngle = 0;

function drawScene()
{
    gl.bindFramebuffer(gl.FRAMEBUFFER, rttFramebuffer);
    drawSceneOnLaptopScreen();
    gl.bindFramebuffer(gl.FRAMEBUFFER, null);

    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);

    mvPushMatrix();

    mat4.translate(mvMatrix, mvMatrix, [0, -0.4, -2.2]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(laptopAngle), [0, 1, 0]);
    mat4.rotate(mvMatrix, mvMatrix, degToRad(-90), [1, 0, 0]);

    gl.uniform1i(shaderProgram.showSpecularHighlightsUniform, true);
    gl.uniform3f(shaderProgram.pointLightingLocationUniform, -1, 2, -1);
    gl.uniform3f(shaderProgram.ambientLightingColorUniform, -1, 2, -1);

    gl.uniform3f(shaderProgram.ambientLightingColorUniform, 0.2, 0.2, 0.2);
    gl.uniform3f(shaderProgram.pointLightingDiffuseColorUniform, 0.8, 0.8, 0.8);
    gl.uniform3f(shaderProgram.pointLightingSpecularColorUniform, 0.8, 0.8, 0.8);


    gl.uniform3f(shaderProgram.materialAmbientColorUniform, 1.0, 1.0, 1.0);
    gl.uniform3f(shaderProgram.materialDiffuseColorUniform, 1.0, 1.0, 1.0);
    gl.uniform3f(shaderProgram.materialSpecularColorUniform, 1.5, 1.5, 1.5);
    gl.uniform1f(shaderProgram.materialShininessUniform, 5);
    gl.uniform3f(shaderProgram.materialEmissiveColorUniform, 0.0, 0.0, 0.0);
    gl.uniform1i(shaderProgram.useTexturesUniform, false);

    if (laptopVertexPositionBuffer) 
    {
        gl.bindBuffer(gl.ARRAY_BUFFER, laptopVertexPositionBuffer);
        gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 
            laptopVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

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

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

        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, laptopVertexIndexBuffer);
        setMatrixUniforms();
        gl.drawElements(gl.TRIANGLES, 
            laptopVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
    }

    gl.uniform3f(shaderProgram.materialAmbientColorUniform, 0.0, 0.0, 0.0);
    gl.uniform3f(shaderProgram.materialDiffuseColorUniform, 0.0, 0.0, 0.0);
    gl.uniform3f(shaderProgram.materialSpecularColorUniform, 0.5, 0.5, 0.5);
    gl.uniform1f(shaderProgram.materialShininessUniform, 20);
    gl.uniform3f(shaderProgram.materialEmissiveColorUniform, 1.5, 1.5, 1.5);
    gl.uniform1i(shaderProgram.useTexturesUniform, true);

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

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

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

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

    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 
        laptopScreenVertexPositionBuffer.numItems);

    mvPopMatrix();
}

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;

        moonAngle += 0.05 * elapsed;
        cubeAngle += 0.05 * elapsed;

        laptopAngle -= 0.005 * elapsed;
    }
    lastTime = timeNow;
}
</script>