/*
Copyright (C) 2011 Apple Computer, Inc.  All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

function webglTestLog(msg) {
  if (window.console && window.console.log) {
    window.console.log(msg);
  }
  if (document.getElementById("console")) {
    var log = document.getElementById("console");
    log.innerHTML += msg + "<br>";
  }
}

//
// create3DContext
//
// Returns the WebGLRenderingContext for any known implementation.
//
function create3DContext(canvas, attributes)
{
    if (!canvas)
        canvas = document.createElement("canvas");
    var context = null;
    try {
        context = canvas.getContext("webgl", attributes);
    } catch(e) {}
    if (!context) {
        try {
            context = canvas.getContext("experimental-webgl", attributes);
        } catch(e) {}
    }
    if (!context) {
        throw "Unable to fetch WebGL rendering context for Canvas";
    }
    return context;
}

function createGLErrorWrapper(context, fname) {
    return function() {
        var rv = context[fname].apply(context, arguments);
        var err = context.getError();
        if (err != 0)
            throw "GL error " + err + " in " + fname;
        return rv;
    };
}

function create3DContextWithWrapperThatThrowsOnGLError(canvas, attributes) {
  var context = create3DContext(canvas, attributes);
  // Thanks to Ilmari Heikkinen for the idea on how to implement this so elegantly.
  var wrap = {};
  for (var i in context) {
    try {
      if (typeof context[i] == 'function') {
        wrap[i] = createGLErrorWrapper(context, i);
      } else {
        wrap[i] = context[i];
      }
    } catch (e) {
      webglTestLog("createContextWrapperThatThrowsOnGLError: Error accessing " + i);
    }
  }
  wrap.getError = function() {
      return context.getError();
  };
  return wrap;
}

function getGLErrorAsString(ctx, err) {
  if (err === ctx.NO_ERROR) {
    return "NO_ERROR";
  }
  for (var name in ctx) {
    if (ctx[name] === err) {
      return name;
    }
  }
  return "0x" + err.toString(16);
}

// Pass undefined for glError to test that it at least throws some error
function shouldGenerateGLError(ctx, glErrors, evalStr) {
  if (!glErrors.length) {
    glErrors = [glErrors];
  }
  var exception;
  try {
    eval(evalStr);
  } catch (e) {
    exception = e;
  }
  if (exception) {
    testFailed(evalStr + " threw exception " + exception);
  } else {
    var err = ctx.getError();
    if (glErrors.indexOf(err) < 0) {
      var errStrs = [];
      for (var ii = 0; ii < glErrors.length; ++ii) {
        errStrs.push(getGLErrorAsString(ctx, glErrors[ii]));
      }
      testFailed(evalStr + " expected: " + errStrs.join(" or ") + ". Was " + getGLErrorAsString(ctx, err) + ".");
    } else {
      testPassed(evalStr + " generated expected GL error: " + getGLErrorAsString(ctx, err) + ".");
    }
  }
}

/**
 * Tests that the first error GL returns is the specified error.
 * @param {!WebGLContext} gl The WebGLContext to use.
 * @param {number} glError The expected gl error.
 * @param {string} opt_msg Optional additional message.
 */
function glErrorShouldBe(gl, glError, opt_msg) {
  opt_msg = opt_msg || "";
  var err = gl.getError();
  if (err != glError) {
    testFailed("getError expected: " + getGLErrorAsString(gl, glError) +
               ". Was " + getGLErrorAsString(gl, err) + " : " + opt_msg);
  } else {
    testPassed("getError was expected value: " +
                getGLErrorAsString(gl, glError) + " : " + opt_msg);
  }
};

//
// createProgram
//
// Create and return a program object, attaching each of the given shaders.
//
// If attribs are given, bind an attrib with that name at that index.
//
function createProgram(gl, vshaders, fshaders, attribs)
{
  if (typeof(vshaders) == "string")
    vshaders = [vshaders];
  if (typeof(fshaders) == "string")
    fshaders = [fshaders];

  var shaders = [];
  var i;

  for (i = 0; i < vshaders.length; ++i) {
    var shader = loadShader(gl, vshaders[i], gl.VERTEX_SHADER);
    if (!shader)
      return null;
    shaders.push(shader);
  }

  for (i = 0; i < fshaders.length; ++i) {
    var shader = loadShader(gl, fshaders[i], gl.FRAGMENT_SHADER);
    if (!shader)
      return null;
    shaders.push(shader);
  }

  var prog = gl.createProgram();
  for (i = 0; i < shaders.length; ++i) {
    gl.attachShader(prog, shaders[i]);
  }

  if (attribs) {
    for (var i = 0; i < attribs.length; ++i) {
      gl.bindAttribLocation(prog, i, attribs[i]);
    }
  }

  gl.linkProgram(prog);

  // Check the link status
  var linked = gl.getProgramParameter(prog, gl.LINK_STATUS);
  if (!linked) {
    // something went wrong with the link
    var error = gl.getProgramInfoLog(prog);
    webglTestLog("Error in program linking:" + error);

    gl.deleteProgram(prog);
    for (i = 0; i < shaders.length; ++i)
      gl.deleteShader(shaders[i]);
    return null;
  }

  return prog;
}

//
// initWebGL
//
// Initialize the Canvas element with the passed name as a WebGL object and return the
// WebGLRenderingContext.
//
// Load shaders with the passed names and create a program with them. Return this program
// in the 'program' property of the returned context.
//
// For each string in the passed attribs array, bind an attrib with that name at that index.
// Once the attribs are bound, link the program and then use it.
//
// Set the clear color to the passed array (4 values) and set the clear depth to the passed value.
// Enable depth testing and blending with a blend func of (SRC_ALPHA, ONE_MINUS_SRC_ALPHA)
//
function initWebGL(canvasName, vshader, fshader, attribs, clearColor, clearDepth, contextAttribs)
{
    var canvas = document.getElementById(canvasName);
    var gl = create3DContext(canvas, contextAttribs);
    if (!gl) {
        alert("No WebGL context found");
        return null;
    }

    // Create the program object
    gl.program = createProgram(gl, vshader, fshader, attribs);
    if (!gl.program)
        return null;

    gl.useProgram(gl.program);

    gl.clearColor(clearColor[0], clearColor[1], clearColor[2], clearColor[3]);
    gl.clearDepth(clearDepth);

    gl.enable(gl.DEPTH_TEST);
    gl.enable(gl.BLEND);
    gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);

    return gl;
}

//
// getShaderSource
//
// Load the source from the passed shader file.
//
function getShaderSource(file)
{
    var xhr = new XMLHttpRequest();
    xhr.open("GET", file, false);
    xhr.send();
    return xhr.responseText;
}


//
// loadShader
//
// 'shader' is either the id of a <script> element containing the shader source
// string, the shader string itself,  or the URL of a file containing the shader
// source. Load this shader and return the WebGLShader object corresponding to
// it.
//
function loadShader(ctx, shaderId, shaderType, isFile)
{
    var shaderSource = "";

    if (isFile)
        shaderSource = getShaderSource(shaderId);
    else {
        var shaderScript = document.getElementById(shaderId);
        if (!shaderScript) {
            shaderSource = shaderId;
        } else {
            if (shaderScript.type == "x-shader/x-vertex") {
                shaderType = ctx.VERTEX_SHADER;
            } else if (shaderScript.type == "x-shader/x-fragment") {
                shaderType = ctx.FRAGMENT_SHADER;
            } else if (shaderType != ctx.VERTEX_SHADER && shaderType != ctx.FRAGMENT_SHADER) {
                webglTestLog("*** Error: unknown shader type");
                return null;
            }

            shaderSource = shaderScript.text;
        }
    }

    // Create the shader object
    var shader = ctx.createShader(shaderType);
    if (shader == null) {
        webglTestLog("*** Error: unable to create shader '"+shaderId+"'");
        return null;
    }

    // Load the shader source
    ctx.shaderSource(shader, shaderSource);

    // Compile the shader
    ctx.compileShader(shader);

    // Check the compile status
    var compiled = ctx.getShaderParameter(shader, ctx.COMPILE_STATUS);
    if (!compiled) {
        // Something went wrong during compilation; get the error
        var error = ctx.getShaderInfoLog(shader);
        webglTestLog("*** Error compiling shader '"+shader+"':"+error);
        ctx.deleteShader(shader);
        return null;
    }

    return shader;
}

function loadShaderFromFile(ctx, file, type)
{
    return loadShader(ctx, file, type, true);
}

function loadShaderFromScript(ctx, script)
{
    return loadShader(ctx, script, 0, false);
}

function loadStandardProgram(context) {
    var program = context.createProgram();
    context.attachShader(program, loadStandardVertexShader(context));
    context.attachShader(program, loadStandardFragmentShader(context));
    context.linkProgram(program);
    return program;
}

function loadProgram(context, vertexShaderPath, fragmentShaderPath, isFile) {
    isFile = (isFile === undefined) ? true : isFile;
    var program = context.createProgram();
    context.attachShader(program, loadShader(context, vertexShaderPath, context.VERTEX_SHADER, isFile));
    context.attachShader(program, loadShader(context, fragmentShaderPath, context.FRAGMENT_SHADER, isFile));
    context.linkProgram(program);
    return program;
}

var getBasePathForResources = function() {
  var expectedBase = "webgl-test.js";
  var scripts = document.getElementsByTagName('script');
  for (var script, i = 0; script = scripts[i]; i++) {
    var src = script.src;
    var l = src.length;
    if (src.substr(l - expectedBase.length) == expectedBase) {
      return src.substr(0, l - expectedBase.length);
    }
  }
  throw 'oops';
};


function loadStandardVertexShader(context) {
    return loadShader(
        context, 
        getBasePathForResources() + "vertexShader.vert", 
        context.VERTEX_SHADER, 
        true); 
}

function loadStandardFragmentShader(context) {
    return loadShader(
        context, 
        getBasePathForResources() + "fragmentShader.frag", 
        context.FRAGMENT_SHADER, 
        true); 
}

//
// makeBox
//
// Create a box with vertices, normals and texCoords. Create VBOs for each as well as the index array.
// Return an object with the following properties:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
//
function makeBox(ctx)
{
    // box
    //    v6----- v5
    //   /|      /|
    //  v1------v0|
    //  | |     | |
    //  | |v7---|-|v4
    //  |/      |/
    //  v2------v3
    //
    // vertex coords array
    var vertices = new Float32Array(
        [  1, 1, 1,  -1, 1, 1,  -1,-1, 1,   1,-1, 1,    // v0-v1-v2-v3 front
           1, 1, 1,   1,-1, 1,   1,-1,-1,   1, 1,-1,    // v0-v3-v4-v5 right
           1, 1, 1,   1, 1,-1,  -1, 1,-1,  -1, 1, 1,    // v0-v5-v6-v1 top
          -1, 1, 1,  -1, 1,-1,  -1,-1,-1,  -1,-1, 1,    // v1-v6-v7-v2 left
          -1,-1,-1,   1,-1,-1,   1,-1, 1,  -1,-1, 1,    // v7-v4-v3-v2 bottom
           1,-1,-1,  -1,-1,-1,  -1, 1,-1,   1, 1,-1 ]   // v4-v7-v6-v5 back
    );

    // normal array
    var normals = new Float32Array(
        [  0, 0, 1,   0, 0, 1,   0, 0, 1,   0, 0, 1,     // v0-v1-v2-v3 front
           1, 0, 0,   1, 0, 0,   1, 0, 0,   1, 0, 0,     // v0-v3-v4-v5 right
           0, 1, 0,   0, 1, 0,   0, 1, 0,   0, 1, 0,     // v0-v5-v6-v1 top
          -1, 0, 0,  -1, 0, 0,  -1, 0, 0,  -1, 0, 0,     // v1-v6-v7-v2 left
           0,-1, 0,   0,-1, 0,   0,-1, 0,   0,-1, 0,     // v7-v4-v3-v2 bottom
           0, 0,-1,   0, 0,-1,   0, 0,-1,   0, 0,-1 ]    // v4-v7-v6-v5 back
       );


    // texCoord array
    var texCoords = new Float32Array(
        [  1, 1,   0, 1,   0, 0,   1, 0,    // v0-v1-v2-v3 front
           0, 1,   0, 0,   1, 0,   1, 1,    // v0-v3-v4-v5 right
           1, 0,   1, 1,   0, 1,   0, 0,    // v0-v5-v6-v1 top
           1, 1,   0, 1,   0, 0,   1, 0,    // v1-v6-v7-v2 left
           0, 0,   1, 0,   1, 1,   0, 1,    // v7-v4-v3-v2 bottom
           0, 0,   1, 0,   1, 1,   0, 1 ]   // v4-v7-v6-v5 back
       );

    // index array
    var indices = new Uint8Array(
        [  0, 1, 2,   0, 2, 3,    // front
           4, 5, 6,   4, 6, 7,    // right
           8, 9,10,   8,10,11,    // top
          12,13,14,  12,14,15,    // left
          16,17,18,  16,18,19,    // bottom
          20,21,22,  20,22,23 ]   // back
      );

    var retval = { };

    retval.normalObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.normalObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, normals, ctx.STATIC_DRAW);

    retval.texCoordObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.texCoordObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, texCoords, ctx.STATIC_DRAW);

    retval.vertexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.vertexObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, vertices, ctx.STATIC_DRAW);

    ctx.bindBuffer(ctx.ARRAY_BUFFER, 0);

    retval.indexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, retval.indexObject);
    ctx.bufferData(ctx.ELEMENT_ARRAY_BUFFER, indices, ctx.STATIC_DRAW);
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, 0);

    retval.numIndices = indices.length;

    return retval;
}

//
// makeSphere
//
// Create a sphere with the passed number of latitude and longitude bands and the passed radius.
// Sphere has vertices, normals and texCoords. Create VBOs for each as well as the index array.
// Return an object with the following properties:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
//
function makeSphere(ctx, radius, lats, longs)
{
    var geometryData = [ ];
    var normalData = [ ];
    var texCoordData = [ ];
    var indexData = [ ];

    for (var latNumber = 0; latNumber <= lats; ++latNumber) {
        for (var longNumber = 0; longNumber <= longs; ++longNumber) {
            var theta = latNumber * Math.PI / lats;
            var phi = longNumber * 2 * Math.PI / longs;
            var sinTheta = Math.sin(theta);
            var sinPhi = Math.sin(phi);
            var cosTheta = Math.cos(theta);
            var cosPhi = Math.cos(phi);

            var x = cosPhi * sinTheta;
            var y = cosTheta;
            var z = sinPhi * sinTheta;
            var u = 1-(longNumber/longs);
            var v = latNumber/lats;

            normalData.push(x);
            normalData.push(y);
            normalData.push(z);
            texCoordData.push(u);
            texCoordData.push(v);
            geometryData.push(radius * x);
            geometryData.push(radius * y);
            geometryData.push(radius * z);
        }
    }

    longs += 1;
    for (var latNumber = 0; latNumber < lats; ++latNumber) {
        for (var longNumber = 0; longNumber < longs; ++longNumber) {
            var first = (latNumber * longs) + (longNumber % longs);
            var second = first + longs;
            indexData.push(first);
            indexData.push(second);
            indexData.push(first+1);

            indexData.push(second);
            indexData.push(second+1);
            indexData.push(first+1);
        }
    }

    var retval = { };

    retval.normalObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.normalObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new Float32Array(normalData), ctx.STATIC_DRAW);

    retval.texCoordObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.texCoordObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new Float32Array(texCoordData), ctx.STATIC_DRAW);

    retval.vertexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.vertexObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new Float32Array(geometryData), ctx.STATIC_DRAW);

    retval.numIndices = indexData.length;
    retval.indexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, retval.indexObject);
    ctx.bufferData(ctx.ELEMENT_ARRAY_BUFFER, new Uint16Array(indexData), ctx.STREAM_DRAW);

    return retval;
}

//
// loadObj
//
// Load a .obj file from the passed URL. Return an object with a 'loaded' property set to false.
// When the object load is complete, the 'loaded' property becomes true and the following
// properties are set:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
//
function loadObj(ctx, url)
{
    var obj = { loaded : false };
    obj.ctx = ctx;
    var req = new XMLHttpRequest();
    req.obj = obj;
    req.onreadystatechange = function () { processLoadObj(req) };
    req.open("GET", url, true);
    req.send(null);
    return obj;
}

function processLoadObj(req)
{
    webglTestLog("req="+req)
    // only if req shows "complete"
    if (req.readyState == 4) {
        doLoadObj(req.obj, req.responseText);
    }
}

function doLoadObj(obj, text)
{
    vertexArray = [ ];
    normalArray = [ ];
    textureArray = [ ];
    indexArray = [ ];

    var vertex = [ ];
    var normal = [ ];
    var texture = [ ];
    var facemap = { };
    var index = 0;

    var lines = text.split("\n");
    for (var lineIndex in lines) {
        var line = lines[lineIndex].replace(/[ \t]+/g, " ").replace(/\s\s*$/, "");

        // ignore comments
        if (line[0] == "#")
            continue;

        var array = line.split(" ");
        if (array[0] == "v") {
            // vertex
            vertex.push(parseFloat(array[1]));
            vertex.push(parseFloat(array[2]));
            vertex.push(parseFloat(array[3]));
        }
        else if (array[0] == "vt") {
            // normal
            texture.push(parseFloat(array[1]));
            texture.push(parseFloat(array[2]));
        }
        else if (array[0] == "vn") {
            // normal
            normal.push(parseFloat(array[1]));
            normal.push(parseFloat(array[2]));
            normal.push(parseFloat(array[3]));
        }
        else if (array[0] == "f") {
            // face
            if (array.length != 4) {
                webglTestLog("*** Error: face '"+line+"' not handled");
                continue;
            }

            for (var i = 1; i < 4; ++i) {
                if (!(array[i] in facemap)) {
                    // add a new entry to the map and arrays
                    var f = array[i].split("/");
                    var vtx, nor, tex;

                    if (f.length == 1) {
                        vtx = parseInt(f[0]) - 1;
                        nor = vtx;
                        tex = vtx;
                    }
                    else if (f.length = 3) {
                        vtx = parseInt(f[0]) - 1;
                        tex = parseInt(f[1]) - 1;
                        nor = parseInt(f[2]) - 1;
                    }
                    else {
                        webglTestLog("*** Error: did not understand face '"+array[i]+"'");
                        return null;
                    }

                    // do the vertices
                    var x = 0;
                    var y = 0;
                    var z = 0;
                    if (vtx * 3 + 2 < vertex.length) {
                        x = vertex[vtx*3];
                        y = vertex[vtx*3+1];
                        z = vertex[vtx*3+2];
                    }
                    vertexArray.push(x);
                    vertexArray.push(y);
                    vertexArray.push(z);

                    // do the textures
                    x = 0;
                    y = 0;
                    if (tex * 2 + 1 < texture.length) {
                        x = texture[tex*2];
                        y = texture[tex*2+1];
                    }
                    textureArray.push(x);
                    textureArray.push(y);

                    // do the normals
                    x = 0;
                    y = 0;
                    z = 1;
                    if (nor * 3 + 2 < normal.length) {
                        x = normal[nor*3];
                        y = normal[nor*3+1];
                        z = normal[nor*3+2];
                    }
                    normalArray.push(x);
                    normalArray.push(y);
                    normalArray.push(z);

                    facemap[array[i]] = index++;
                }

                indexArray.push(facemap[array[i]]);
            }
        }
    }

    // set the VBOs
    obj.normalObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.normalObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new Float32Array(normalArray), obj.ctx.STATIC_DRAW);

    obj.texCoordObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.texCoordObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new Float32Array(textureArray), obj.ctx.STATIC_DRAW);

    obj.vertexObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.vertexObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new Float32Array(vertexArray), obj.ctx.STATIC_DRAW);

    obj.numIndices = indexArray.length;
    obj.indexObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ELEMENT_ARRAY_BUFFER, obj.indexObject);
    obj.ctx.bufferData(obj.ctx.ELEMENT_ARRAY_BUFFER, new Uint16Array(indexArray), obj.ctx.STREAM_DRAW);

    obj.loaded = true;
}

//
// loadImageTexture
//
// Load the image at the passed url, place it in a new WebGLTexture object and return the WebGLTexture.
//
function loadImageTexture(ctx, url)
{
    var texture = ctx.createTexture();
    texture.image = new Image();
    texture.image.onload = function() { doLoadImageTexture(ctx, texture.image, texture) }
    texture.image.src = url;
    return texture;
}

function doLoadImageTexture(ctx, image, texture)
{
    ctx.enable(ctx.TEXTURE_2D);
    ctx.bindTexture(ctx.TEXTURE_2D, texture);
    ctx.texImage2D(ctx.TEXTURE_2D, 0, ctx.RGBA, ctx.RGBA, ctx.UNSIGNED_BYTE, image);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_MAG_FILTER, ctx.LINEAR);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_MIN_FILTER, ctx.LINEAR_MIPMAP_LINEAR);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_WRAP_S, ctx.CLAMP_TO_EDGE);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_WRAP_T, ctx.CLAMP_TO_EDGE);
    ctx.generateMipmap(ctx.TEXTURE_2D)
    ctx.bindTexture(ctx.TEXTURE_2D, 0);
}

//
// Framerate object
//
// This object keeps track of framerate and displays it as the innerHTML text of the
// HTML element with the passed id. Once created you call snapshot at the end
// of every rendering cycle. Every 500ms the framerate is updated in the HTML element.
//
Framerate = function(id)
{
    this.numFramerates = 10;
    this.framerateUpdateInterval = 500;
    this.id = id;

    this.renderTime = -1;
    this.framerates = [ ];
    self = this;
    var fr = function() { self.updateFramerate() }
    setInterval(fr, this.framerateUpdateInterval);
}

Framerate.prototype.updateFramerate = function()
{
    var tot = 0;
    for (var i = 0; i < this.framerates.length; ++i)
        tot += this.framerates[i];

    var framerate = tot / this.framerates.length;
    framerate = Math.round(framerate);
    document.getElementById(this.id).innerHTML = "Framerate:"+framerate+"fps";
}

Framerate.prototype.snapshot = function()
{
    if (this.renderTime < 0)
        this.renderTime = new Date().getTime();
    else {
        var newTime = new Date().getTime();
        var t = newTime - this.renderTime;
        var framerate = 1000/t;
        this.framerates.push(framerate);
        while (this.framerates.length > this.numFramerates)
            this.framerates.shift();
        this.renderTime = newTime;
    }
}
