<img src="/media/img/crate.gif" id="crate" style="position:absolute; top: -300px; left: -300px;"/>
<script id="shader-fs" type="x-shader/x-fragment">
    #ifdef GL_ES
    precision highp float;
    #endif

    varying vec2 vTextureCoord;

    uniform sampler2D uSampler;

    void main(void) {
        gl_FragColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
    }
</script>
<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 type="text/javascript">

    var gl;

    function initGL(canvas) {
        try {
            gl = canvas.getContext("experimental-webgl");
            gl.viewportWidth = canvas.width;
            gl.viewportHeight = canvas.height;
        } catch (e) {
        }
        if (!gl) {
            alert("Could not initialise WebGL, sorry :-(");
        }
    }

    function getShader(gl, id) {
        var shaderScript = document.getElementById(id);
        if (!shaderScript) {
            return null;
        }

        var str = "";
        str += shaderScript.innerHTML;

        var shader;
        if (shaderScript.type == "x-shader/x-fragment") {
            shader = gl.createShader(gl.FRAGMENT_SHADER);
        } else if (shaderScript.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("Could not initialise shaders");
        }

        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");
    }

    function handleLoadedTexture(textures) {
        gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);

        gl.bindTexture(gl.TEXTURE_2D, textures[0]);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, textures[0].image);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

        gl.bindTexture(gl.TEXTURE_2D, textures[1]);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, textures[1].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, textures[2]);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, textures[2].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);
    }

    var crateTextures = Array();

    function initTexture() {
        var crateImage = document.getElementById('crate');
        for (var i=0; i < 3; i++) {
            var texture = gl.createTexture();
            texture.image = crateImage;
            crateTextures.push(texture);
        }

        handleLoadedTexture(crateTextures, true);
    }

    var mvMatrix = mat4.create();
    var mvMatrixStack = [];
    var pMatrix = mat4.create();

    function mvPushMatrix() {
        var copy = mat4.create();
        mat4.set(mvMatrix, copy);
        mvMatrixStack.push(copy);
    }

    function mvPopMatrix() {
        if (mvMatrixStack.length == 0) {
            throw "Invalid popMatrix!";
        }
        mvMatrix = mvMatrixStack.pop();
    }

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

    function degToRad(degrees) {
        return degrees * Math.PI / 180;
    }

    var xRot = 0;
    var xSpeed = 0;

    var yRot = 0;
    var ySpeed = 0;

    var z = -5.0;

    var filter = 0;

    var currentlyPressedKeys = {};

    function handleKeyDown(event) {
    event = event || window.event;
        currentlyPressedKeys[event.keyCode] = true;

        if (String.fromCharCode(event.keyCode) == "F") {
            filter += 1;
            if (filter == 3) {
                filter = 0;
            }
        }
    }

    function handleKeyUp(event) {
    event = event || window.event;
        currentlyPressedKeys[event.keyCode] = false;
    }

    function handleKeys() {
        if (currentlyPressedKeys[33]) {
            // Page Up
            z -= 0.05;
        }
        if (currentlyPressedKeys[34]) {
            // Page Down
            z += 0.05;
        }
        if (currentlyPressedKeys[37]) {
            // Left cursor key
            ySpeed -= 1;
        }
        if (currentlyPressedKeys[39]) {
            // Right cursor key
            ySpeed += 1;
        }
        if (currentlyPressedKeys[38]) {
            // Up cursor key
            xSpeed -= 1;
        }
        if (currentlyPressedKeys[40]) {
            // Down cursor key
            xSpeed += 1;
        }
    }

    var cubeVertexPositionBuffer;
    var cubeVertexTextureCoordBuffer;
    var cubeVertexIndexBuffer;
    function initBuffers() {
        cubeVertexPositionBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
        vertices = [
            // Front face
            -1.0, -1.0,  1.0,
             1.0, -1.0,  1.0,
             1.0,  1.0,  1.0,
            -1.0,  1.0,  1.0,

            // Back face
            -1.0, -1.0, -1.0,
            -1.0,  1.0, -1.0,
             1.0,  1.0, -1.0,
             1.0, -1.0, -1.0,

            // Top face
            -1.0,  1.0, -1.0,
            -1.0,  1.0,  1.0,
             1.0,  1.0,  1.0,
             1.0,  1.0, -1.0,

            // Bottom face
            -1.0, -1.0, -1.0,
             1.0, -1.0, -1.0,
             1.0, -1.0,  1.0,
            -1.0, -1.0,  1.0,

            // Right face
             1.0, -1.0, -1.0,
             1.0,  1.0, -1.0,
             1.0,  1.0,  1.0,
             1.0, -1.0,  1.0,

            // Left face
            -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;

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

            // Back face
            1.0, 0.0,
            1.0, 1.0,
            0.0, 1.0,
            0.0, 0.0,

            // Top face
            0.0, 1.0,
            0.0, 0.0,
            1.0, 0.0,
            1.0, 1.0,

            // Bottom face
            1.0, 1.0,
            0.0, 1.0,
            0.0, 0.0,
            1.0, 0.0,

            // Right face
            1.0, 0.0,
            1.0, 1.0,
            0.0, 1.0,
            0.0, 0.0,

            // Left face
            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,    // Front face
            4, 5, 6,      4, 6, 7,    // Back face
            8, 9, 10,     8, 10, 11,  // Top face
            12, 13, 14,   12, 14, 15, // Bottom face
            16, 17, 18,   16, 18, 19, // Right face
            20, 21, 22,   20, 22, 23  // Left face
        ]
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
        cubeVertexIndexBuffer.itemSize = 1;
        cubeVertexIndexBuffer.numItems = 36;
    }

    function drawScene() {
        gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

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

        mat4.identity(mvMatrix);

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

        mat4.rotate(mvMatrix, degToRad(xRot), [1, 0, 0]);
        mat4.rotate(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, cubeVertexTextureCoordBuffer);
        gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, cubeVertexTextureCoordBuffer.itemSize, gl.FLOAT, false, 0, 0);

        gl.activeTexture(gl.TEXTURE0);
        gl.bindTexture(gl.TEXTURE_2D, crateTextures[filter]);
        gl.uniform1i(shaderProgram.samplerUniform, 0);

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

    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;
    }

    function tick() {
        handleKeys();
        drawScene();
        animate();
        setTimeout(tick, 10);
    }

    function webGLStart() {
        var canvas = document.getElementById("canvas");
        initGL(canvas);
        initShaders();
        initBuffers();
        initTexture();

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

        document.onkeydown = handleKeyDown;
        document.onkeyup = handleKeyUp;

        tick();
    }

    window.onload = function () {
        jebgl(document.getElementById('canvas'), webGLStart, 
              { jebglJar: '/media/jar/jebgl.jar',
                jarLocation: '/media/jar/',
                alwaysApplet: true});
    }

</script>