前端图片验证码（兼容ie8）

╰半橙微兮° 2022-05-29 12:26 200阅读 0赞

让可爱的我mack一下

## 前提 ##

最后会附上源码的~

*  图片验证码插件名称： GVerify.js
    
    > GVerify主要使用canvas生成图片验证码，但是ie8还没有canvas。
 *  针对ie8 解决canvas插件：excanvas.js
    
    > 主要是解决没有canvas方法getContext。
 *  改变html页面为

js部分

this.verifyCode = new GVerify({
        id: "v_container", //容器Id
        type: "number" //图形验证码默认类型blend:数字字母混合类型、number:纯数字、letter:纯字母
    });

对GVerify.js插件做的修改

/**初始化方法**/
        _init: function() {
            var con = document.getElementById(this.options.id);
            // var canvas = document.createElement("canvas");
            //获得画布 IE不能支持canvas，可以增加excanvas.js插件，但是还是不支持createelement()的形式
            var canvas = document.getElementById(this.options.canvasId);
            this.options.width = con.offsetWidth > 0 ? con.offsetWidth : "124";
            this.options.height = con.offsetHeight > 0 ? con.offsetHeight : "35";
            console.log(con, canvas,document.getElementById('img-code'));
    
    
            // 为了兼容ie去掉
            // canvas.id = this.options.canvasId;
            // canvas.width = this.options.width;
            // canvas.height = this.options.height;
            // canvas.style.cursor = "pointer";
            // canvas.innerHTML = "您的浏览器版本不支持canvas";
            // con.appendChild(canvas);
    
    
            var parent = this;
            parent.refresh();
            canvas.onclick = function(){
                parent.refresh();
            }
        },

## 遇到的问题 ##

在某种情况下：比如。图片二维码是append上去的。  
或许你发现在网上下载的excanvas.js出现了有事不生效的情况。  
excanvas.js查看源码发现

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');
    
          使用了事件监听，注释掉直接掉用就可以。
          // doc.attachEvent('onreadystatechange', bind(this.init_, this, 
          this.init_(doc);
          doc));
        },

## 源码保留 ##

### GVerify.js ###

### excanvas.js ###

// 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, '&').replace(/"/g, '"');
      }
    
      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');
          this.init_(doc);
          // doc.attachEvent('onreadystatechange', bind(this.init_, this, doc));
        },
    
        init_: function(doc) { 
          // find all canvas elements
          var els = doc.getElementsByTagName('canvas');
          console.log(els);
          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_;
    })();
    
    }