// Copyright 2006 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.


// Known Issues:
//
// * Patterns only support repeat.
// * Radial gradient are not implemented. The VML version of these look very
//   different from the canvas one.
// * Clipping paths are not implemented.
// * Coordsize. The width and height attribute have higher priority than the
//   width and height style values which isn't correct.
// * Painting mode isn't implemented.
// * Canvas width/height should is using content-box by default. IE in
//   Quirks mode will draw the canvas using border-box. Either change your
//   doctype to HTML5
//   (http://www.whatwg.org/specs/web-apps/current-work/#the-doctype)
//   or use Box Sizing Behavior from WebFX
//   (http://webfx.eae.net/dhtml/boxsizing/boxsizing.html)
// * Non uniform scaling does not correctly scale strokes.
// * Optimize. There is always room for speed improvements.

// Only add this code if we do not already have a canvas implementation
if (!document.createElement('canvas').getContext) {

    (function() {

        // alias some functions to make (compiled) code shorter
        var m = Math;
        var mr = m.round;
        var ms = m.sin;
        var mc = m.cos;
        var abs = m.abs;
        var sqrt = m.sqrt;

        // this is used for sub pixel precision
        var Z = 10;
        var Z2 = Z / 2;

        var IE_VERSION = +navigator.userAgent.match(/MSIE ([\d.]+)?/)[1];

        /**
         * This funtion is assigned to the <canvas> elements as element.getContext().
         * @this {HTMLElement}
         * @return {CanvasRenderingContext2D_}
         */
        function getContext() {
            return this.context_ ||
                (this.context_ = new CanvasRenderingContext2D_(this));
        }

        var slice = Array.prototype.slice;

        /**
         * Binds a function to an object. The returned function will always use the
         * passed in {@code obj} as {@code this}.
         *
         * Example:
         *
         *   g = bind(f, obj, a, b)
         *   g(c, d) // will do f.call(obj, a, b, c, d)
         *
         * @param {Function} f The function to bind the object to
         * @param {Object} obj The object that should act as this when the function
         *     is called
         * @param {*} var_args Rest arguments that will be used as the initial
         *     arguments when the function is called
         * @return {Function} A new function that has bound this
         */
        function bind(f, obj, var_args) {
            var a = slice.call(arguments, 2);
            return function() {
                return f.apply(obj, a.concat(slice.call(arguments)));
            };
        }

        function encodeHtmlAttribute(s) {
            return String(s).replace(/&/g, '&amp;').replace(/"/g, '&quot;');
        }

        function addNamespace(doc, prefix, urn) {
            if (!doc.namespaces[prefix]) {
                doc.namespaces.add(prefix, urn, '#default#VML');
            }
        }

        function addNamespacesAndStylesheet(doc) {
            addNamespace(doc, 'g_vml_', 'urn:schemas-microsoft-com:vml');
            addNamespace(doc, 'g_o_', 'urn:schemas-microsoft-com:office:office');

            // Setup default CSS.  Only add one style sheet per document
            if (!doc.styleSheets['ex_canvas_']) {
                var ss = doc.createStyleSheet();
                ss.owningElement.id = 'ex_canvas_';
                ss.cssText = 'canvas{display:inline-block;overflow:hidden;' +
                    // default size is 300x150 in Gecko and Opera
                    'text-align:left;width:300px;height:150px}';
            }
        }

        // Add namespaces and stylesheet at startup.
        addNamespacesAndStylesheet(document);

        var G_vmlCanvasManager_ = {
            init: function(opt_doc) {
                var doc = opt_doc || document;
                // Create a dummy element so that IE will allow canvas elements to be
                // recognized.
                doc.createElement('canvas');
                doc.attachEvent('onreadystatechange', bind(this.init_, this, doc));
            },

            init_: function(doc) {
                // find all canvas elements
                var els = doc.getElementsByTagName('canvas');
                for (var i = 0; i < els.length; i++) {
                    this.initElement(els[i]);
                }
            },

            /**
             * Public initializes a canvas element so that it can be used as canvas
             * element from now on. This is called automatically before the page is
             * loaded but if you are creating elements using createElement you need to
             * make sure this is called on the element.
             * @param {HTMLElement} el The canvas element to initialize.
             * @return {HTMLElement} the element that was created.
             */
            initElement: function(el) {
                if (!el.getContext) {
                    el.getContext = getContext;

                    // Add namespaces and stylesheet to document of the element.
                    addNamespacesAndStylesheet(el.ownerDocument);

                    // Remove fallback content. There is no way to hide text nodes so we
                    // just remove all childNodes. We could hide all elements and remove
                    // text nodes but who really cares about the fallback content.
                    el.innerHTML = '';

                    // do not use inline function because that will leak memory
                    el.attachEvent('onpropertychange', onPropertyChange);
                    el.attachEvent('onresize', onResize);

                    var attrs = el.attributes;
                    if (attrs.width && attrs.width.specified) {
                        // TODO: use runtimeStyle and coordsize
                        // el.getContext().setWidth_(attrs.width.nodeValue);
                        el.style.width = attrs.width.nodeValue + 'px';
                    } else {
                        el.width = el.clientWidth;
                    }
                    if (attrs.height && attrs.height.specified) {
                        // TODO: use runtimeStyle and coordsize
                        // el.getContext().setHeight_(attrs.height.nodeValue);
                        el.style.height = attrs.height.nodeValue + 'px';
                    } else {
                        el.height = el.clientHeight;
                    }
                    //el.getContext().setCoordsize_()
                }
                return el;
            }
        };

        function onPropertyChange(e) {
            var el = e.srcElement;

            switch (e.propertyName) {
                case 'width':
                    el.getContext().clearRect();
                    el.style.width = el.attributes.width.nodeValue + 'px';
                    // In IE8 this does not trigger onresize.
                    el.firstChild.style.width =  el.clientWidth + 'px';
                    break;
                case 'height':
                    el.getContext().clearRect();
                    el.style.height = el.attributes.height.nodeValue + 'px';
                    el.firstChild.style.height = el.clientHeight + 'px';
                    break;
            }
        }

        function onResize(e) {
            var el = e.srcElement;
            if (el.firstChild) {
                el.firstChild.style.width =  el.clientWidth + 'px';
                el.firstChild.style.height = el.clientHeight + 'px';
            }
        }

        G_vmlCanvasManager_.init();

        // precompute "00" to "FF"
        var decToHex = [];
        for (var i = 0; i < 16; i++) {
            for (var j = 0; j < 16; j++) {
                decToHex[i * 16 + j] = i.toString(16) + j.toString(16);
            }
        }

        function createMatrixIdentity() {
            return [
                [1, 0, 0],
                [0, 1, 0],
                [0, 0, 1]
            ];
        }

        function matrixMultiply(m1, m2) {
            var result = createMatrixIdentity();

            for (var x = 0; x < 3; x++) {
                for (var y = 0; y < 3; y++) {
                    var sum = 0;

                    for (var z = 0; z < 3; z++) {
                        sum += m1[x][z] * m2[z][y];
                    }

                    result[x][y] = sum;
                }
            }
            return result;
        }

        function copyState(o1, o2) {
            o2.fillStyle     = o1.fillStyle;
            o2.lineCap       = o1.lineCap;
            o2.lineJoin      = o1.lineJoin;
            o2.lineWidth     = o1.lineWidth;
            o2.miterLimit    = o1.miterLimit;
            o2.shadowBlur    = o1.shadowBlur;
            o2.shadowColor   = o1.shadowColor;
            o2.shadowOffsetX = o1.shadowOffsetX;
            o2.shadowOffsetY = o1.shadowOffsetY;
            o2.strokeStyle   = o1.strokeStyle;
            o2.globalAlpha   = o1.globalAlpha;
            o2.font          = o1.font;
            o2.textAlign     = o1.textAlign;
            o2.textBaseline  = o1.textBaseline;
            o2.arcScaleX_    = o1.arcScaleX_;
            o2.arcScaleY_    = o1.arcScaleY_;
            o2.lineScale_    = o1.lineScale_;
        }

        var colorData = {
            aliceblue: '#F0F8FF',
            antiquewhite: '#FAEBD7',
            aquamarine: '#7FFFD4',
            azure: '#F0FFFF',
            beige: '#F5F5DC',
            bisque: '#FFE4C4',
            black: '#000000',
            blanchedalmond: '#FFEBCD',
            blueviolet: '#8A2BE2',
            brown: '#A52A2A',
            burlywood: '#DEB887',
            cadetblue: '#5F9EA0',
            chartreuse: '#7FFF00',
            chocolate: '#D2691E',
            coral: '#FF7F50',
            cornflowerblue: '#6495ED',
            cornsilk: '#FFF8DC',
            crimson: '#DC143C',
            cyan: '#00FFFF',
            darkblue: '#00008B',
            darkcyan: '#008B8B',
            darkgoldenrod: '#B8860B',
            darkgray: '#A9A9A9',
            darkgreen: '#006400',
            darkgrey: '#A9A9A9',
            darkkhaki: '#BDB76B',
            darkmagenta: '#8B008B',
            darkolivegreen: '#556B2F',
            darkorange: '#FF8C00',
            darkorchid: '#9932CC',
            darkred: '#8B0000',
            darksalmon: '#E9967A',
            darkseagreen: '#8FBC8F',
            darkslateblue: '#483D8B',
            darkslategray: '#2F4F4F',
            darkslategrey: '#2F4F4F',
            darkturquoise: '#00CED1',
            darkviolet: '#9400D3',
            deeppink: '#FF1493',
            deepskyblue: '#00BFFF',
            dimgray: '#696969',
            dimgrey: '#696969',
            dodgerblue: '#1E90FF',
            firebrick: '#B22222',
            floralwhite: '#FFFAF0',
            forestgreen: '#228B22',
            gainsboro: '#DCDCDC',
            ghostwhite: '#F8F8FF',
            gold: '#FFD700',
            goldenrod: '#DAA520',
            grey: '#808080',
            greenyellow: '#ADFF2F',
            honeydew: '#F0FFF0',
            hotpink: '#FF69B4',
            indianred: '#CD5C5C',
            indigo: '#4B0082',
            ivory: '#FFFFF0',
            khaki: '#F0E68C',
            lavender: '#E6E6FA',
            lavenderblush: '#FFF0F5',
            lawngreen: '#7CFC00',
            lemonchiffon: '#FFFACD',
            lightblue: '#ADD8E6',
            lightcoral: '#F08080',
            lightcyan: '#E0FFFF',
            lightgoldenrodyellow: '#FAFAD2',
            lightgreen: '#90EE90',
            lightgrey: '#D3D3D3',
            lightpink: '#FFB6C1',
            lightsalmon: '#FFA07A',
            lightseagreen: '#20B2AA',
            lightskyblue: '#87CEFA',
            lightslategray: '#778899',
            lightslategrey: '#778899',
            lightsteelblue: '#B0C4DE',
            lightyellow: '#FFFFE0',
            limegreen: '#32CD32',
            linen: '#FAF0E6',
            magenta: '#FF00FF',
            mediumaquamarine: '#66CDAA',
            mediumblue: '#0000CD',
            mediumorchid: '#BA55D3',
            mediumpurple: '#9370DB',
            mediumseagreen: '#3CB371',
            mediumslateblue: '#7B68EE',
            mediumspringgreen: '#00FA9A',
            mediumturquoise: '#48D1CC',
            mediumvioletred: '#C71585',
            midnightblue: '#191970',
            mintcream: '#F5FFFA',
            mistyrose: '#FFE4E1',
            moccasin: '#FFE4B5',
            navajowhite: '#FFDEAD',
            oldlace: '#FDF5E6',
            olivedrab: '#6B8E23',
            orange: '#FFA500',
            orangered: '#FF4500',
            orchid: '#DA70D6',
            palegoldenrod: '#EEE8AA',
            palegreen: '#98FB98',
            paleturquoise: '#AFEEEE',
            palevioletred: '#DB7093',
            papayawhip: '#FFEFD5',
            peachpuff: '#FFDAB9',
            peru: '#CD853F',
            pink: '#FFC0CB',
            plum: '#DDA0DD',
            powderblue: '#B0E0E6',
            rosybrown: '#BC8F8F',
            royalblue: '#4169E1',
            saddlebrown: '#8B4513',
            salmon: '#FA8072',
            sandybrown: '#F4A460',
            seagreen: '#2E8B57',
            seashell: '#FFF5EE',
            sienna: '#A0522D',
            skyblue: '#87CEEB',
            slateblue: '#6A5ACD',
            slategray: '#708090',
            slategrey: '#708090',
            snow: '#FFFAFA',
            springgreen: '#00FF7F',
            steelblue: '#4682B4',
            tan: '#D2B48C',
            thistle: '#D8BFD8',
            tomato: '#FF6347',
            turquoise: '#40E0D0',
            violet: '#EE82EE',
            wheat: '#F5DEB3',
            whitesmoke: '#F5F5F5',
            yellowgreen: '#9ACD32'
        };


        function getRgbHslContent(styleString) {
            var start = styleString.indexOf('(', 3);
            var end = styleString.indexOf(')', start + 1);
            var parts = styleString.substring(start + 1, end).split(',');
            // add alpha if needed
            if (parts.length != 4 || styleString.charAt(3) != 'a') {
                parts[3] = 1;
            }
            return parts;
        }

        function percent(s) {
            return parseFloat(s) / 100;
        }

        function clamp(v, min, max) {
            return Math.min(max, Math.max(min, v));
        }

        function hslToRgb(parts){
            var r, g, b, h, s, l;
            h = parseFloat(parts[0]) / 360 % 360;
            if (h < 0)
                h++;
            s = clamp(percent(parts[1]), 0, 1);
            l = clamp(percent(parts[2]), 0, 1);
            if (s == 0) {
                r = g = b = l; // achromatic
            } else {
                var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
                var p = 2 * l - q;
                r = hueToRgb(p, q, h + 1 / 3);
                g = hueToRgb(p, q, h);
                b = hueToRgb(p, q, h - 1 / 3);
            }

            return '#' + decToHex[Math.floor(r * 255)] +
                decToHex[Math.floor(g * 255)] +
                decToHex[Math.floor(b * 255)];
        }

        function hueToRgb(m1, m2, h) {
            if (h < 0)
                h++;
            if (h > 1)
                h--;

            if (6 * h < 1)
                return m1 + (m2 - m1) * 6 * h;
            else if (2 * h < 1)
                return m2;
            else if (3 * h < 2)
                return m1 + (m2 - m1) * (2 / 3 - h) * 6;
            else
                return m1;
        }

        var processStyleCache = {};

        function processStyle(styleString) {
            if (styleString in processStyleCache) {
                return processStyleCache[styleString];
            }

            var str, alpha = 1;

            styleString = String(styleString);
            if (styleString.charAt(0) == '#') {
                str = styleString;
            } else if (/^rgb/.test(styleString)) {
                var parts = getRgbHslContent(styleString);
                var str = '#', n;
                for (var i = 0; i < 3; i++) {
                    if (parts[i].indexOf('%') != -1) {
                        n = Math.floor(percent(parts[i]) * 255);
                    } else {
                        n = +parts[i];
                    }
                    str += decToHex[clamp(n, 0, 255)];
                }
                alpha = +parts[3];
            } else if (/^hsl/.test(styleString)) {
                var parts = getRgbHslContent(styleString);
                str = hslToRgb(parts);
                alpha = parts[3];
            } else {
                str = colorData[styleString] || styleString;
            }
            return processStyleCache[styleString] = {color: str, alpha: alpha};
        }

        var DEFAULT_STYLE = {
            style: 'normal',
            variant: 'normal',
            weight: 'normal',
            size: 10,
            family: 'sans-serif'
        };

        // Internal text style cache
        var fontStyleCache = {};

        function processFontStyle(styleString) {
            if (fontStyleCache[styleString]) {
                return fontStyleCache[styleString];
            }

            var el = document.createElement('div');
            var style = el.style;
            try {
                style.font = styleString;
            } catch (ex) {
                // Ignore failures to set to invalid font.
            }

            return fontStyleCache[styleString] = {
                style: style.fontStyle || DEFAULT_STYLE.style,
                variant: style.fontVariant || DEFAULT_STYLE.variant,
                weight: style.fontWeight || DEFAULT_STYLE.weight,
                size: style.fontSize || DEFAULT_STYLE.size,
                family: style.fontFamily || DEFAULT_STYLE.family
            };
        }

        function getComputedStyle(style, element) {
            var computedStyle = {};

            for (var p in style) {
                computedStyle[p] = style[p];
            }

            // Compute the size
            var canvasFontSize = parseFloat(element.currentStyle.fontSize),
                fontSize = parseFloat(style.size);

            if (typeof style.size == 'number') {
                computedStyle.size = style.size;
            } else if (style.size.indexOf('px') != -1) {
                computedStyle.size = fontSize;
            } else if (style.size.indexOf('em') != -1) {
                computedStyle.size = canvasFontSize * fontSize;
            } else if(style.size.indexOf('%') != -1) {
                computedStyle.size = (canvasFontSize / 100) * fontSize;
            } else if (style.size.indexOf('pt') != -1) {
                computedStyle.size = fontSize / .75;
            } else {
                computedStyle.size = canvasFontSize;
            }

            // Different scaling between normal text and VML text. This was found using
            // trial and error to get the same size as non VML text.
            computedStyle.size *= 0.981;

            return computedStyle;
        }

        function buildStyle(style) {
            return style.style + ' ' + style.variant + ' ' + style.weight + ' ' +
                style.size + 'px ' + style.family;
        }

        var lineCapMap = {
            'butt': 'flat',
            'round': 'round'
        };

        function processLineCap(lineCap) {
            return lineCapMap[lineCap] || 'square';
        }

        /**
         * This class implements CanvasRenderingContext2D interface as described by
         * the WHATWG.
         * @param {HTMLElement} canvasElement The element that the 2D context should
         * be associated with
         */
        function CanvasRenderingContext2D_(canvasElement) {
            this.m_ = createMatrixIdentity();

            this.mStack_ = [];
            this.aStack_ = [];
            this.currentPath_ = [];

            // Canvas context properties
            this.strokeStyle = '#000';
            this.fillStyle = '#000';

            this.lineWidth = 1;
            this.lineJoin = 'miter';
            this.lineCap = 'butt';
            this.miterLimit = Z * 1;
            this.globalAlpha = 1;
            this.font = '10px sans-serif';
            this.textAlign = 'left';
            this.textBaseline = 'alphabetic';
            this.canvas = canvasElement;

            var cssText = 'width:' + canvasElement.clientWidth + 'px;height:' +
                canvasElement.clientHeight + 'px;overflow:hidden;position:absolute';
            var el = canvasElement.ownerDocument.createElement('div');
            el.style.cssText = cssText;
            canvasElement.appendChild(el);

            var overlayEl = el.cloneNode(false);
            // Use a non transparent background.
            overlayEl.style.backgroundColor = 'red';
            overlayEl.style.filter = 'alpha(opacity=0)';
            canvasElement.appendChild(overlayEl);

            this.element_ = el;
            this.arcScaleX_ = 1;
            this.arcScaleY_ = 1;
            this.lineScale_ = 1;
        }

        var contextPrototype = CanvasRenderingContext2D_.prototype;
        contextPrototype.clearRect = function() {
            if (this.textMeasureEl_) {
                this.textMeasureEl_.removeNode(true);
                this.textMeasureEl_ = null;
            }
            this.element_.innerHTML = '';
        };

        contextPrototype.beginPath = function() {
            // TODO: Branch current matrix so that save/restore has no effect
            //       as per safari docs.
            this.currentPath_ = [];
        };

        contextPrototype.moveTo = function(aX, aY) {
            var p = getCoords(this, aX, aY);
            this.currentPath_.push({type: 'moveTo', x: p.x, y: p.y});
            this.currentX_ = p.x;
            this.currentY_ = p.y;
        };

        contextPrototype.lineTo = function(aX, aY) {
            var p = getCoords(this, aX, aY);
            this.currentPath_.push({type: 'lineTo', x: p.x, y: p.y});

            this.currentX_ = p.x;
            this.currentY_ = p.y;
        };

        contextPrototype.bezierCurveTo = function(aCP1x, aCP1y,
                                                  aCP2x, aCP2y,
                                                  aX, aY) {
            var p = getCoords(this, aX, aY);
            var cp1 = getCoords(this, aCP1x, aCP1y);
            var cp2 = getCoords(this, aCP2x, aCP2y);
            bezierCurveTo(this, cp1, cp2, p);
        };

        // Helper function that takes the already fixed cordinates.
        function bezierCurveTo(self, cp1, cp2, p) {
            self.currentPath_.push({
                type: 'bezierCurveTo',
                cp1x: cp1.x,
                cp1y: cp1.y,
                cp2x: cp2.x,
                cp2y: cp2.y,
                x: p.x,
                y: p.y
            });
            self.currentX_ = p.x;
            self.currentY_ = p.y;
        }

        contextPrototype.quadraticCurveTo = function(aCPx, aCPy, aX, aY) {
            // the following is lifted almost directly from
            // http://developer.mozilla.org/en/docs/Canvas_tutorial:Drawing_shapes

            var cp = getCoords(this, aCPx, aCPy);
            var p = getCoords(this, aX, aY);

            var cp1 = {
                x: this.currentX_ + 2.0 / 3.0 * (cp.x - this.currentX_),
                y: this.currentY_ + 2.0 / 3.0 * (cp.y - this.currentY_)
            };
            var cp2 = {
                x: cp1.x + (p.x - this.currentX_) / 3.0,
                y: cp1.y + (p.y - this.currentY_) / 3.0
            };

            bezierCurveTo(this, cp1, cp2, p);
        };

        contextPrototype.arc = function(aX, aY, aRadius,
                                        aStartAngle, aEndAngle, aClockwise) {
            aRadius *= Z;
            var arcType = aClockwise ? 'at' : 'wa';

            var xStart = aX + mc(aStartAngle) * aRadius - Z2;
            var yStart = aY + ms(aStartAngle) * aRadius - Z2;

            var xEnd = aX + mc(aEndAngle) * aRadius - Z2;
            var yEnd = aY + ms(aEndAngle) * aRadius - Z2;

            // IE won't render arches drawn counter clockwise if xStart == xEnd.
            if (xStart == xEnd && !aClockwise) {
                xStart += 0.125; // Offset xStart by 1/80 of a pixel. Use something
                                 // that can be represented in binary
            }

            var p = getCoords(this, aX, aY);
            var pStart = getCoords(this, xStart, yStart);
            var pEnd = getCoords(this, xEnd, yEnd);

            this.currentPath_.push({type: arcType,
                x: p.x,
                y: p.y,
                radius: aRadius,
                xStart: pStart.x,
                yStart: pStart.y,
                xEnd: pEnd.x,
                yEnd: pEnd.y});

        };

        contextPrototype.rect = function(aX, aY, aWidth, aHeight) {
            this.moveTo(aX, aY);
            this.lineTo(aX + aWidth, aY);
            this.lineTo(aX + aWidth, aY + aHeight);
            this.lineTo(aX, aY + aHeight);
            this.closePath();
        };

        contextPrototype.strokeRect = function(aX, aY, aWidth, aHeight) {
            var oldPath = this.currentPath_;
            this.beginPath();

            this.moveTo(aX, aY);
            this.lineTo(aX + aWidth, aY);
            this.lineTo(aX + aWidth, aY + aHeight);
            this.lineTo(aX, aY + aHeight);
            this.closePath();
            this.stroke();

            this.currentPath_ = oldPath;
        };

        contextPrototype.fillRect = function(aX, aY, aWidth, aHeight) {
            var oldPath = this.currentPath_;
            this.beginPath();

            this.moveTo(aX, aY);
            this.lineTo(aX + aWidth, aY);
            this.lineTo(aX + aWidth, aY + aHeight);
            this.lineTo(aX, aY + aHeight);
            this.closePath();
            this.fill();

            this.currentPath_ = oldPath;
        };

        contextPrototype.createLinearGradient = function(aX0, aY0, aX1, aY1) {
            var gradient = new CanvasGradient_('gradient');
            gradient.x0_ = aX0;
            gradient.y0_ = aY0;
            gradient.x1_ = aX1;
            gradient.y1_ = aY1;
            return gradient;
        };

        contextPrototype.createRadialGradient = function(aX0, aY0, aR0,
                                                         aX1, aY1, aR1) {
            var gradient = new CanvasGradient_('gradientradial');
            gradient.x0_ = aX0;
            gradient.y0_ = aY0;
            gradient.r0_ = aR0;
            gradient.x1_ = aX1;
            gradient.y1_ = aY1;
            gradient.r1_ = aR1;
            return gradient;
        };

        contextPrototype.drawImage = function(image, var_args) {
            var dx, dy, dw, dh, sx, sy, sw, sh;

            // to find the original width we overide the width and height
            var oldRuntimeWidth = image.runtimeStyle.width;
            var oldRuntimeHeight = image.runtimeStyle.height;
            image.runtimeStyle.width = 'auto';
            image.runtimeStyle.height = 'auto';

            // get the original size
            var w = image.width;
            var h = image.height;

            // and remove overides
            image.runtimeStyle.width = oldRuntimeWidth;
            image.runtimeStyle.height = oldRuntimeHeight;

            if (arguments.length == 3) {
                dx = arguments[1];
                dy = arguments[2];
                sx = sy = 0;
                sw = dw = w;
                sh = dh = h;
            } else if (arguments.length == 5) {
                dx = arguments[1];
                dy = arguments[2];
                dw = arguments[3];
                dh = arguments[4];
                sx = sy = 0;
                sw = w;
                sh = h;
            } else if (arguments.length == 9) {
                sx = arguments[1];
                sy = arguments[2];
                sw = arguments[3];
                sh = arguments[4];
                dx = arguments[5];
                dy = arguments[6];
                dw = arguments[7];
                dh = arguments[8];
            } else {
                throw Error('Invalid number of arguments');
            }

            var d = getCoords(this, dx, dy);

            var w2 = sw / 2;
            var h2 = sh / 2;

            var vmlStr = [];

            var W = 10;
            var H = 10;

            // For some reason that I've now forgotten, using divs didn't work
            vmlStr.push(' <g_vml_:group',
                ' coordsize="', Z * W, ',', Z * H, '"',
                ' coordorigin="0,0"' ,
                ' style="width:', W, 'px;height:', H, 'px;position:absolute;');

            // If filters are necessary (rotation exists), create them
            // filters are bog-slow, so only create them if abbsolutely necessary
            // The following check doesn't account for skews (which don't exist
            // in the canvas spec (yet) anyway.

            if (this.m_[0][0] != 1 || this.m_[0][1] ||
                this.m_[1][1] != 1 || this.m_[1][0]) {
                var filter = [];

                // Note the 12/21 reversal
                filter.push('M11=', this.m_[0][0], ',',
                    'M12=', this.m_[1][0], ',',
                    'M21=', this.m_[0][1], ',',
                    'M22=', this.m_[1][1], ',',
                    'Dx=', mr(d.x / Z), ',',
                    'Dy=', mr(d.y / Z), '');

                // Bounding box calculation (need to minimize displayed area so that
                // filters don't waste time on unused pixels.
                var max = d;
                var c2 = getCoords(this, dx + dw, dy);
                var c3 = getCoords(this, dx, dy + dh);
                var c4 = getCoords(this, dx + dw, dy + dh);

                max.x = m.max(max.x, c2.x, c3.x, c4.x);
                max.y = m.max(max.y, c2.y, c3.y, c4.y);

                vmlStr.push('padding:0 ', mr(max.x / Z), 'px ', mr(max.y / Z),
                    'px 0;filter:progid:DXImageTransform.Microsoft.Matrix(',
                    filter.join(''), ", sizingmethod='clip');");

            } else {
                vmlStr.push('top:', mr(d.y / Z), 'px;left:', mr(d.x / Z), 'px;');
            }

            vmlStr.push(' ">' ,
                '<g_vml_:image src="', image.src, '"',
                ' style="width:', Z * dw, 'px;',
                ' height:', Z * dh, 'px"',
                ' cropleft="', sx / w, '"',
                ' croptop="', sy / h, '"',
                ' cropright="', (w - sx - sw) / w, '"',
                ' cropbottom="', (h - sy - sh) / h, '"',
                ' />',
                '</g_vml_:group>');

            this.element_.insertAdjacentHTML('BeforeEnd', vmlStr.join(''));
        };

        contextPrototype.stroke = function(aFill) {
            var lineStr = [];
            var lineOpen = false;

            var W = 10;
            var H = 10;

            lineStr.push('<g_vml_:shape',
                ' filled="', !!aFill, '"',
                ' style="position:absolute;width:', W, 'px;height:', H, 'px;"',
                ' coordorigin="0,0"',
                ' coordsize="', Z * W, ',', Z * H, '"',
                ' stroked="', !aFill, '"',
                ' path="');

            var newSeq = false;
            var min = {x: null, y: null};
            var max = {x: null, y: null};

            for (var i = 0; i < this.currentPath_.length; i++) {
                var p = this.currentPath_[i];
                var c;

                switch (p.type) {
                    case 'moveTo':
                        c = p;
                        lineStr.push(' m ', mr(p.x), ',', mr(p.y));
                        break;
                    case 'lineTo':
                        lineStr.push(' l ', mr(p.x), ',', mr(p.y));
                        break;
                    case 'close':
                        lineStr.push(' x ');
                        p = null;
                        break;
                    case 'bezierCurveTo':
                        lineStr.push(' c ',
                            mr(p.cp1x), ',', mr(p.cp1y), ',',
                            mr(p.cp2x), ',', mr(p.cp2y), ',',
                            mr(p.x), ',', mr(p.y));
                        break;
                    case 'at':
                    case 'wa':
                        lineStr.push(' ', p.type, ' ',
                            mr(p.x - this.arcScaleX_ * p.radius), ',',
                            mr(p.y - this.arcScaleY_ * p.radius), ' ',
                            mr(p.x + this.arcScaleX_ * p.radius), ',',
                            mr(p.y + this.arcScaleY_ * p.radius), ' ',
                            mr(p.xStart), ',', mr(p.yStart), ' ',
                            mr(p.xEnd), ',', mr(p.yEnd));
                        break;
                }


                // TODO: Following is broken for curves due to
                //       move to proper paths.

                // Figure out dimensions so we can do gradient fills
                // properly
                if (p) {
                    if (min.x == null || p.x < min.x) {
                        min.x = p.x;
                    }
                    if (max.x == null || p.x > max.x) {
                        max.x = p.x;
                    }
                    if (min.y == null || p.y < min.y) {
                        min.y = p.y;
                    }
                    if (max.y == null || p.y > max.y) {
                        max.y = p.y;
                    }
                }
            }
            lineStr.push(' ">');

            if (!aFill) {
                appendStroke(this, lineStr);
            } else {
                appendFill(this, lineStr, min, max);
            }

            lineStr.push('</g_vml_:shape>');

            this.element_.insertAdjacentHTML('beforeEnd', lineStr.join(''));
        };

        function appendStroke(ctx, lineStr) {
            var a = processStyle(ctx.strokeStyle);
            var color = a.color;
            var opacity = a.alpha * ctx.globalAlpha;
            var lineWidth = ctx.lineScale_ * ctx.lineWidth;

            // VML cannot correctly render a line if the width is less than 1px.
            // In that case, we dilute the color to make the line look thinner.
            if (lineWidth < 1) {
                opacity *= lineWidth;
            }

            lineStr.push(
                '<g_vml_:stroke',
                ' opacity="', opacity, '"',
                ' joinstyle="', ctx.lineJoin, '"',
                ' miterlimit="', ctx.miterLimit, '"',
                ' endcap="', processLineCap(ctx.lineCap), '"',
                ' weight="', lineWidth, 'px"',
                ' color="', color, '" />'
            );
        }

        function appendFill(ctx, lineStr, min, max) {
            var fillStyle = ctx.fillStyle;
            var arcScaleX = ctx.arcScaleX_;
            var arcScaleY = ctx.arcScaleY_;
            var width = max.x - min.x;
            var height = max.y - min.y;
            if (fillStyle instanceof CanvasGradient_) {
                // TODO: Gradients transformed with the transformation matrix.
                var angle = 0;
                var focus = {x: 0, y: 0};

                // additional offset
                var shift = 0;
                // scale factor for offset
                var expansion = 1;

                if (fillStyle.type_ == 'gradient') {
                    var x0 = fillStyle.x0_ / arcScaleX;
                    var y0 = fillStyle.y0_ / arcScaleY;
                    var x1 = fillStyle.x1_ / arcScaleX;
                    var y1 = fillStyle.y1_ / arcScaleY;
                    var p0 = getCoords(ctx, x0, y0);
                    var p1 = getCoords(ctx, x1, y1);
                    var dx = p1.x - p0.x;
                    var dy = p1.y - p0.y;
                    angle = Math.atan2(dx, dy) * 180 / Math.PI;

                    // The angle should be a non-negative number.
                    if (angle < 0) {
                        angle += 360;
                    }

                    // Very small angles produce an unexpected result because they are
                    // converted to a scientific notation string.
                    if (angle < 1e-6) {
                        angle = 0;
                    }
                } else {
                    var p0 = getCoords(ctx, fillStyle.x0_, fillStyle.y0_);
                    focus = {
                        x: (p0.x - min.x) / width,
                        y: (p0.y - min.y) / height
                    };

                    width  /= arcScaleX * Z;
                    height /= arcScaleY * Z;
                    var dimension = m.max(width, height);
                    shift = 2 * fillStyle.r0_ / dimension;
                    expansion = 2 * fillStyle.r1_ / dimension - shift;
                }

                // We need to sort the color stops in ascending order by offset,
                // otherwise IE won't interpret it correctly.
                var stops = fillStyle.colors_;
                stops.sort(function(cs1, cs2) {
                    return cs1.offset - cs2.offset;
                });

                var length = stops.length;
                var color1 = stops[0].color;
                var color2 = stops[length - 1].color;
                var opacity1 = stops[0].alpha * ctx.globalAlpha;
                var opacity2 = stops[length - 1].alpha * ctx.globalAlpha;

                var colors = [];
                for (var i = 0; i < length; i++) {
                    var stop = stops[i];
                    colors.push(stop.offset * expansion + shift + ' ' + stop.color);
                }

                // When colors attribute is used, the meanings of opacity and o:opacity2
                // are reversed.
                lineStr.push('<g_vml_:fill type="', fillStyle.type_, '"',
                    ' method="none" focus="100%"',
                    ' color="', color1, '"',
                    ' color2="', color2, '"',
                    ' colors="', colors.join(','), '"',
                    ' opacity="', opacity2, '"',
                    ' g_o_:opacity2="', opacity1, '"',
                    ' angle="', angle, '"',
                    ' focusposition="', focus.x, ',', focus.y, '" />');
            } else if (fillStyle instanceof CanvasPattern_) {
                if (width && height) {
                    var deltaLeft = -min.x;
                    var deltaTop = -min.y;
                    lineStr.push('<g_vml_:fill',
                        ' position="',
                        deltaLeft / width * arcScaleX * arcScaleX, ',',
                        deltaTop / height * arcScaleY * arcScaleY, '"',
                        ' type="tile"',
                        // TODO: Figure out the correct size to fit the scale.
                        //' size="', w, 'px ', h, 'px"',
                        ' src="', fillStyle.src_, '" />');
                }
            } else {
                var a = processStyle(ctx.fillStyle);
                var color = a.color;
                var opacity = a.alpha * ctx.globalAlpha;
                lineStr.push('<g_vml_:fill color="', color, '" opacity="', opacity,
                    '" />');
            }
        }

        contextPrototype.fill = function() {
            this.stroke(true);
        };

        contextPrototype.closePath = function() {
            this.currentPath_.push({type: 'close'});
        };

        function getCoords(ctx, aX, aY) {
            var m = ctx.m_;
            return {
                x: Z * (aX * m[0][0] + aY * m[1][0] + m[2][0]) - Z2,
                y: Z * (aX * m[0][1] + aY * m[1][1] + m[2][1]) - Z2
            };
        };

        contextPrototype.save = function() {
            var o = {};
            copyState(this, o);
            this.aStack_.push(o);
            this.mStack_.push(this.m_);
            this.m_ = matrixMultiply(createMatrixIdentity(), this.m_);
        };

        contextPrototype.restore = function() {
            if (this.aStack_.length) {
                copyState(this.aStack_.pop(), this);
                this.m_ = this.mStack_.pop();
            }
        };

        function matrixIsFinite(m) {
            return isFinite(m[0][0]) && isFinite(m[0][1]) &&
                isFinite(m[1][0]) && isFinite(m[1][1]) &&
                isFinite(m[2][0]) && isFinite(m[2][1]);
        }

        function setM(ctx, m, updateLineScale) {
            if (!matrixIsFinite(m)) {
                return;
            }
            ctx.m_ = m;

            if (updateLineScale) {
                // Get the line scale.
                // Determinant of this.m_ means how much the area is enlarged by the
                // transformation. So its square root can be used as a scale factor
                // for width.
                var det = m[0][0] * m[1][1] - m[0][1] * m[1][0];
                ctx.lineScale_ = sqrt(abs(det));
            }
        }

        contextPrototype.translate = function(aX, aY) {
            var m1 = [
                [1,  0,  0],
                [0,  1,  0],
                [aX, aY, 1]
            ];

            setM(this, matrixMultiply(m1, this.m_), false);
        };

        contextPrototype.rotate = function(aRot) {
            var c = mc(aRot);
            var s = ms(aRot);

            var m1 = [
                [c,  s, 0],
                [-s, c, 0],
                [0,  0, 1]
            ];

            setM(this, matrixMultiply(m1, this.m_), false);
        };

        contextPrototype.scale = function(aX, aY) {
            this.arcScaleX_ *= aX;
            this.arcScaleY_ *= aY;
            var m1 = [
                [aX, 0,  0],
                [0,  aY, 0],
                [0,  0,  1]
            ];

            setM(this, matrixMultiply(m1, this.m_), true);
        };

        contextPrototype.transform = function(m11, m12, m21, m22, dx, dy) {
            var m1 = [
                [m11, m12, 0],
                [m21, m22, 0],
                [dx,  dy,  1]
            ];

            setM(this, matrixMultiply(m1, this.m_), true);
        };

        contextPrototype.setTransform = function(m11, m12, m21, m22, dx, dy) {
            var m = [
                [m11, m12, 0],
                [m21, m22, 0],
                [dx,  dy,  1]
            ];

            setM(this, m, true);
        };

        /**
         * The text drawing function.
         * The maxWidth argument isn't taken in account, since no browser supports
         * it yet.
         */
        contextPrototype.drawText_ = function(text, x, y, maxWidth, stroke) {
            var m = this.m_,
                delta = 1000,
                left = 0,
                right = delta,
                offset = {x: 0, y: 0},
                lineStr = [];

            var fontStyle = getComputedStyle(processFontStyle(this.font),
                this.element_);

            var fontStyleString = buildStyle(fontStyle);

            var elementStyle = this.element_.currentStyle;
            var textAlign = this.textAlign.toLowerCase();
            switch (textAlign) {
                case 'left':
                case 'center':
                case 'right':
                    break;
                case 'end':
                    textAlign = elementStyle.direction == 'ltr' ? 'right' : 'left';
                    break;
                case 'start':
                    textAlign = elementStyle.direction == 'rtl' ? 'right' : 'left';
                    break;
                default:
                    textAlign = 'left';
            }

            // 1.75 is an arbitrary number, as there is no info about the text baseline
            switch (this.textBaseline) {
                case 'hanging':
                case 'top':
                    offset.y = fontStyle.size / 1.75;
                    break;
                case 'middle':
                    break;
                default:
                case null:
                case 'alphabetic':
                case 'ideographic':
                case 'bottom':
                    offset.y = -fontStyle.size / 2.25;
                    break;
            }

            switch(textAlign) {
                case 'right':
                    left = delta;
                    right = 0.05;
                    break;
                case 'center':
                    left = right = delta / 2;
                    break;
            }

            var d = getCoords(this, x + offset.x, y + offset.y);

            lineStr.push('<g_vml_:line from="', -left ,' 0" to="', right ,' 0.05" ',
                ' coordsize="100 100" coordorigin="0 0"',
                ' filled="', !stroke, '" stroked="', !!stroke,
                '" style="position:absolute;width:1px;height:1px;">');

            if (stroke) {
                appendStroke(this, lineStr);
            } else {
                // TODO: Fix the min and max params.
                appendFill(this, lineStr, {x: -left, y: 0},
                    {x: right, y: fontStyle.size});
            }

            var skewM = m[0][0].toFixed(3) + ',' + m[1][0].toFixed(3) + ',' +
                m[0][1].toFixed(3) + ',' + m[1][1].toFixed(3) + ',0,0';

            var skewOffset = mr(d.x / Z) + ',' + mr(d.y / Z);

            lineStr.push('<g_vml_:skew on="t" matrix="', skewM ,'" ',
                ' offset="', skewOffset, '" origin="', left ,' 0" />',
                '<g_vml_:path textpathok="true" />',
                '<g_vml_:textpath on="true" string="',
                encodeHtmlAttribute(text),
                '" style="v-text-align:', textAlign,
                ';font:', encodeHtmlAttribute(fontStyleString),
                '" /></g_vml_:line>');

            this.element_.insertAdjacentHTML('beforeEnd', lineStr.join(''));
        };

        contextPrototype.fillText = function(text, x, y, maxWidth) {
            this.drawText_(text, x, y, maxWidth, false);
        };

        contextPrototype.strokeText = function(text, x, y, maxWidth) {
            this.drawText_(text, x, y, maxWidth, true);
        };

        contextPrototype.measureText = function(text) {
            if (!this.textMeasureEl_) {
                var s = '<span style="position:absolute;' +
                    'top:-20000px;left:0;padding:0;margin:0;border:none;' +
                    'white-space:pre;"></span>';
                this.element_.insertAdjacentHTML('beforeEnd', s);
                this.textMeasureEl_ = this.element_.lastChild;
            }
            var doc = this.element_.ownerDocument;
            this.textMeasureEl_.innerHTML = '';
            this.textMeasureEl_.style.font = this.font;
            // Don't use innerHTML or innerText because they allow markup/whitespace.
            this.textMeasureEl_.appendChild(doc.createTextNode(text));
            return {width: this.textMeasureEl_.offsetWidth};
        };

        /******** STUBS ********/
        contextPrototype.clip = function() {
            // TODO: Implement
        };

        contextPrototype.arcTo = function() {
            // TODO: Implement
        };

        contextPrototype.createPattern = function(image, repetition) {
            return new CanvasPattern_(image, repetition);
        };

        // Gradient / Pattern Stubs
        function CanvasGradient_(aType) {
            this.type_ = aType;
            this.x0_ = 0;
            this.y0_ = 0;
            this.r0_ = 0;
            this.x1_ = 0;
            this.y1_ = 0;
            this.r1_ = 0;
            this.colors_ = [];
        }

        CanvasGradient_.prototype.addColorStop = function(aOffset, aColor) {
            aColor = processStyle(aColor);
            this.colors_.push({offset: aOffset,
                color: aColor.color,
                alpha: aColor.alpha});
        };

        function CanvasPattern_(image, repetition) {
            assertImageIsValid(image);
            switch (repetition) {
                case 'repeat':
                case null:
                case '':
                    this.repetition_ = 'repeat';
                    break
                case 'repeat-x':
                case 'repeat-y':
                case 'no-repeat':
                    this.repetition_ = repetition;
                    break;
                default:
                    throwException('SYNTAX_ERR');
            }

            this.src_ = image.src;
            this.width_ = image.width;
            this.height_ = image.height;
        }

        function throwException(s) {
            throw new DOMException_(s);
        }

        function assertImageIsValid(img) {
            if (!img || img.nodeType != 1 || img.tagName != 'IMG') {
                throwException('TYPE_MISMATCH_ERR');
            }
            if (img.readyState != 'complete') {
                throwException('INVALID_STATE_ERR');
            }
        }

        function DOMException_(s) {
            this.code = this[s];
            this.message = s +': DOM Exception ' + this.code;
        }
        var p = DOMException_.prototype = new Error;
        p.INDEX_SIZE_ERR = 1;
        p.DOMSTRING_SIZE_ERR = 2;
        p.HIERARCHY_REQUEST_ERR = 3;
        p.WRONG_DOCUMENT_ERR = 4;
        p.INVALID_CHARACTER_ERR = 5;
        p.NO_DATA_ALLOWED_ERR = 6;
        p.NO_MODIFICATION_ALLOWED_ERR = 7;
        p.NOT_FOUND_ERR = 8;
        p.NOT_SUPPORTED_ERR = 9;
        p.INUSE_ATTRIBUTE_ERR = 10;
        p.INVALID_STATE_ERR = 11;
        p.SYNTAX_ERR = 12;
        p.INVALID_MODIFICATION_ERR = 13;
        p.NAMESPACE_ERR = 14;
        p.INVALID_ACCESS_ERR = 15;
        p.VALIDATION_ERR = 16;
        p.TYPE_MISMATCH_ERR = 17;

        // set up externs
        G_vmlCanvasManager = G_vmlCanvasManager_;
        CanvasRenderingContext2D = CanvasRenderingContext2D_;
        CanvasGradient = CanvasGradient_;
        CanvasPattern = CanvasPattern_;
        DOMException = DOMException_;
    })();

} // if