canvas2svg.js

/*!!
 *  Canvas 2 Svg v1.0.15
 *  A low level canvas to SVG converter. Uses a mock canvas context to build an SVG document.
 *
 *  Licensed under the MIT license:
 *  http://www.opensource.org/licenses/mit-license.php
 *
 *  Author:
 *  Kerry Liu
 *
 *  Copyright (c) 2014 Gliffy Inc.
 */

;(function() {
    "use strict";

    var STYLES, ctx, CanvasGradient, CanvasPattern, namedEntities;

    //helper function to format a string
    function format(str, args) {
        var keys = Object.keys(args), i;
        for (i=0; i<keys.length; i++) {
            str = str.replace(new RegExp("\\{" + keys[i] + "\\}", "gi"), args[keys[i]]);
        }
        return str;
    }

    //helper function that generates a random string
    function randomString(holder) {
        var chars, randomstring, i;
        if (!holder) {
            throw new Error("cannot create a random attribute name for an undefined object");
        }
        chars = "ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";
        randomstring = "";
        do {
            randomstring = "";
            for (i = 0; i < 12; i++) {
                randomstring += chars[Math.floor(Math.random() * chars.length)];
            }
        } while (holder[randomstring]);
        return randomstring;
    }

    //helper function to map named to numbered entities
    function createNamedToNumberedLookup(items, radix) {
        var i, entity, lookup = {}, base10, base16;
        items = items.split(',');
        radix = radix || 10;
        // Map from named to numbered entities.
        for (i = 0; i < items.length; i += 2) {
            entity = '&' + items[i + 1] + ';';
            base10 = parseInt(items[i], radix);
            lookup[entity] = '&#'+base10+';';
        }
        //FF and IE need to create a regex from hex values ie &nbsp; == \xa0
        lookup["\\xa0"] = '&#160;';
        return lookup;
    }

    //helper function to map canvas-textAlign to svg-textAnchor
    function getTextAnchor(textAlign) {
        //TODO: support rtl languages
        var mapping = {"left":"start", "right":"end", "center":"middle", "start":"start", "end":"end"};
        return mapping[textAlign] || mapping.start;
    }

    //helper function to map canvas-textBaseline to svg-dominantBaseline
    function getDominantBaseline(textBaseline) {
        //INFO: not supported in all browsers
        var mapping = {"alphabetic": "alphabetic", "hanging": "hanging", "top":"text-before-edge", "bottom":"text-after-edge", "middle":"central"};
        return mapping[textBaseline] || mapping.alphabetic;
    }

    /**
     * Creates the specified svg element
     * @private
     */
    function createElement(elementName, properties, resetFill) {
        if (typeof properties === "undefined") {
            properties = {};
        }

        var element = document.createElementNS("http://www.w3.org/2000/svg", elementName),
            keys = Object.keys(properties), i, key;
        if(resetFill) {
            //if fill or stroke is not specified, the svg element should not display. By default SVG's fill is black.
            element.setAttribute("fill", "none");
            element.setAttribute("stroke", "none");
        }
        for(i=0; i<keys.length; i++) {
            key = keys[i];
            element.setAttribute(key, properties[key]);
        }
        return element;
    }

    // Unpack entities lookup where the numbers are in radix 32 to reduce the size
    // entity mapping courtesy of tinymce
    namedEntities = createNamedToNumberedLookup(
        '50,nbsp,51,iexcl,52,cent,53,pound,54,curren,55,yen,56,brvbar,57,sect,58,uml,59,copy,' +
            '5a,ordf,5b,laquo,5c,not,5d,shy,5e,reg,5f,macr,5g,deg,5h,plusmn,5i,sup2,5j,sup3,5k,acute,' +
            '5l,micro,5m,para,5n,middot,5o,cedil,5p,sup1,5q,ordm,5r,raquo,5s,frac14,5t,frac12,5u,frac34,' +
            '5v,iquest,60,Agrave,61,Aacute,62,Acirc,63,Atilde,64,Auml,65,Aring,66,AElig,67,Ccedil,' +
            '68,Egrave,69,Eacute,6a,Ecirc,6b,Euml,6c,Igrave,6d,Iacute,6e,Icirc,6f,Iuml,6g,ETH,6h,Ntilde,' +
            '6i,Ograve,6j,Oacute,6k,Ocirc,6l,Otilde,6m,Ouml,6n,times,6o,Oslash,6p,Ugrave,6q,Uacute,' +
            '6r,Ucirc,6s,Uuml,6t,Yacute,6u,THORN,6v,szlig,70,agrave,71,aacute,72,acirc,73,atilde,74,auml,' +
            '75,aring,76,aelig,77,ccedil,78,egrave,79,eacute,7a,ecirc,7b,euml,7c,igrave,7d,iacute,7e,icirc,' +
            '7f,iuml,7g,eth,7h,ntilde,7i,ograve,7j,oacute,7k,ocirc,7l,otilde,7m,ouml,7n,divide,7o,oslash,' +
            '7p,ugrave,7q,uacute,7r,ucirc,7s,uuml,7t,yacute,7u,thorn,7v,yuml,ci,fnof,sh,Alpha,si,Beta,' +
            'sj,Gamma,sk,Delta,sl,Epsilon,sm,Zeta,sn,Eta,so,Theta,sp,Iota,sq,Kappa,sr,Lambda,ss,Mu,' +
            'st,Nu,su,Xi,sv,Omicron,t0,Pi,t1,Rho,t3,Sigma,t4,Tau,t5,Upsilon,t6,Phi,t7,Chi,t8,Psi,' +
            't9,Omega,th,alpha,ti,beta,tj,gamma,tk,delta,tl,epsilon,tm,zeta,tn,eta,to,theta,tp,iota,' +
            'tq,kappa,tr,lambda,ts,mu,tt,nu,tu,xi,tv,omicron,u0,pi,u1,rho,u2,sigmaf,u3,sigma,u4,tau,' +
            'u5,upsilon,u6,phi,u7,chi,u8,psi,u9,omega,uh,thetasym,ui,upsih,um,piv,812,bull,816,hellip,' +
            '81i,prime,81j,Prime,81u,oline,824,frasl,88o,weierp,88h,image,88s,real,892,trade,89l,alefsym,' +
            '8cg,larr,8ch,uarr,8ci,rarr,8cj,darr,8ck,harr,8dl,crarr,8eg,lArr,8eh,uArr,8ei,rArr,8ej,dArr,' +
            '8ek,hArr,8g0,forall,8g2,part,8g3,exist,8g5,empty,8g7,nabla,8g8,isin,8g9,notin,8gb,ni,8gf,prod,' +
            '8gh,sum,8gi,minus,8gn,lowast,8gq,radic,8gt,prop,8gu,infin,8h0,ang,8h7,and,8h8,or,8h9,cap,8ha,cup,' +
            '8hb,int,8hk,there4,8hs,sim,8i5,cong,8i8,asymp,8j0,ne,8j1,equiv,8j4,le,8j5,ge,8k2,sub,8k3,sup,8k4,' +
            'nsub,8k6,sube,8k7,supe,8kl,oplus,8kn,otimes,8l5,perp,8m5,sdot,8o8,lceil,8o9,rceil,8oa,lfloor,8ob,' +
            'rfloor,8p9,lang,8pa,rang,9ea,loz,9j0,spades,9j3,clubs,9j5,hearts,9j6,diams,ai,OElig,aj,oelig,b0,' +
            'Scaron,b1,scaron,bo,Yuml,m6,circ,ms,tilde,802,ensp,803,emsp,809,thinsp,80c,zwnj,80d,zwj,80e,lrm,' +
            '80f,rlm,80j,ndash,80k,mdash,80o,lsquo,80p,rsquo,80q,sbquo,80s,ldquo,80t,rdquo,80u,bdquo,810,dagger,' +
            '811,Dagger,81g,permil,81p,lsaquo,81q,rsaquo,85c,euro', 32);


    //Some basic mappings for attributes and default values.
    STYLES = {
        "strokeStyle":{
            svgAttr : "stroke", //corresponding svg attribute
            canvas : "#000000", //canvas default
            svg : "none",       //svg default
            apply : "stroke"    //apply on stroke() or fill()
        },
        "fillStyle":{
            svgAttr : "fill",
            canvas : "#000000",
            svg : null, //svg default is black, but we need to special case this to handle canvas stroke without fill
            apply : "fill"
        },
        "lineCap":{
            svgAttr : "stroke-linecap",
            canvas : "butt",
            svg : "butt",
            apply : "stroke"
        },
        "lineJoin":{
            svgAttr : "stroke-linejoin",
            canvas : "miter",
            svg : "miter",
            apply : "stroke"
        },
        "miterLimit":{
            svgAttr : "stroke-miterlimit",
            canvas : 10,
            svg : 4,
            apply : "stroke"
        },
        "lineWidth":{
            svgAttr : "stroke-width",
            canvas : 1,
            svg : 1,
            apply : "stroke"
        },
        "globalAlpha": {
            svgAttr : "opacity",
            canvas : 1,
            svg : 1,
            apply : "fill stroke"
        },
        "font":{
            //font converts to multiple svg attributes, there is custom logic for this
            canvas : "10px sans-serif"
        },
        "shadowColor":{
            canvas : "#000000"
        },
        "shadowOffsetX":{
            canvas : 0
        },
        "shadowOffsetY":{
            canvas : 0
        },
        "shadowBlur":{
            canvas : 0
        },
        "textAlign":{
            canvas : "start"
        },
        "textBaseline":{
            canvas : "alphabetic"
        }
    };

    /**
     *
     * @param gradientNode - reference to the gradient
     * @constructor
     */
    CanvasGradient = function(gradientNode) {
        this.__root = gradientNode;
    };

    /**
     * Adds a color stop to the gradient root
     */
    CanvasGradient.prototype.addColorStop = function(offset, color) {
        var stop = createElement("stop"), regex, matches;
        stop.setAttribute("offset", offset);
        if(color.indexOf("rgba") !== -1) {
            //separate alpha value, since webkit can't handle it
            regex = /rgba\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d?\.?\d*)\s*\)/gi;
            matches = regex.exec(color);
            stop.setAttribute("stop-color", format("rgb({r},{g},{b})", {r:matches[1], g:matches[2], b:matches[3]}));
            stop.setAttribute("stop-opacity", matches[4]);
        } else {
            stop.setAttribute("stop-color", color);
        }
        this.__root.appendChild(stop);
    };

    CanvasPattern = function(pattern, ctx) {
        this.__root = pattern;
        this.__ctx = ctx;
    };

    /**
     * The mock canvas context
     * @param o - options include:
     * width - width of your canvas (defaults to 500)
     * height - height of your canvas (defaults to 500)
     * enableMirroring - enables canvas mirroring (get image data) (defaults to false)
     */
    ctx = function(o) {

        var defaultOptions = { width:500, height:500, enableMirroring : false }, options;

        //keep support for this way of calling C2S: new C2S(width,height)
        if(arguments.length > 1) {
            options = defaultOptions;
            options.width = arguments[0];
            options.height = arguments[1];
        } else if( !o ) {
            options = defaultOptions;
        } else {
            options = o;
        }

        if(!(this instanceof ctx)) {
            //did someone call this without new?
            return new ctx(options);
        }

        //setup options
        this.width = options.width || defaultOptions.width;
        this.height = options.height || defaultOptions.height;
        this.enableMirroring = options.enableMirroring !== undefined ? options.enableMirroring : defaultOptions.enableMirroring;

        this.canvas = this;   ///point back to this instance!
        this.__canvas = document.createElement("canvas");
        this.__ctx = this.__canvas.getContext("2d");

        this.__setDefaultStyles();
        this.__stack = [this.__getStyleState()];
        this.__groupStack = [];

        //the root svg element
        this.__root = document.createElementNS("http://www.w3.org/2000/svg", "svg");
        this.__root.setAttribute("version", 1.1);
        this.__root.setAttribute("xmlns", "http://www.w3.org/2000/svg");
        this.__root.setAttributeNS("http://www.w3.org/2000/xmlns/", "xmlns:xlink", "http://www.w3.org/1999/xlink");
        this.__root.setAttribute("width", this.width);
        this.__root.setAttribute("height", this.height);

        //make sure we don't generate the same ids in defs
        this.__ids = {};

        //defs tag
        this.__defs = document.createElementNS("http://www.w3.org/2000/svg", "defs");
        this.__root.appendChild(this.__defs);

        //also add a group child. the svg element can't use the transform attribute
        this.__currentElement = document.createElementNS("http://www.w3.org/2000/svg", "g");
        this.__root.appendChild(this.__currentElement);
    };

    /**
     * Applies default canvas styles to the context
     * @private
     */
    ctx.prototype.__setDefaultStyles = function() {
        //default 2d canvas context properties see:http://www.w3.org/TR/2dcontext/
        var keys = Object.keys(STYLES), i, key;
        for(i=0; i<keys.length; i++) {
            key = keys[i];
            this[key] = STYLES[key].canvas;
        }
    };

    /**
     * Applies styles on restore
     * @param styleState
     * @private
     */
    ctx.prototype.__applyStyleState = function(styleState) {
        var keys = Object.keys(styleState), i, key;
        for(i=0; i<keys.length; i++) {
            key = keys[i];
            this[key] = styleState[key];
        }
    };

    /**
     * Gets the current style state
     * @return {Object}
     * @private
     */
    ctx.prototype.__getStyleState = function() {
        var i, styleState = {}, keys = Object.keys(STYLES), key;
        for(i=0; i<keys.length; i++) {
            key = keys[i];
            styleState[key] = this[key];
        }
        return styleState;
    };

    /**
     * Apples the current styles to the current SVG element. On "ctx.fill" or "ctx.stroke"
     * @param type
     * @private
     */
    ctx.prototype.__applyStyleToCurrentElement = function(type) {
        var keys = Object.keys(STYLES), i, style, value, id, regex, matches;
        for(i=0; i<keys.length; i++) {
            style = STYLES[keys[i]];
            value = this[keys[i]];
            if(style.apply) {
                //is this a gradient or pattern?
                if(style.apply.indexOf("fill")!==-1 && value instanceof CanvasPattern) {
                    //pattern
                    if(value.__ctx) {
                        //copy over defs
                        while(value.__ctx.__defs.childNodes.length) {
                            id = value.__ctx.__defs.childNodes[0].getAttribute("id");
                            this.__ids[id] = id;
                            this.__defs.appendChild(value.__ctx.__defs.childNodes[0]);
                        }
                    }
                    this.__currentElement.setAttribute("fill", format("url(#{id})", {id:value.__root.getAttribute("id")}));
                }
                else if(style.apply.indexOf("fill")!==-1 && value instanceof CanvasGradient) {
                    //gradient
                    this.__currentElement.setAttribute("fill", format("url(#{id})", {id:value.__root.getAttribute("id")}));
                } else if(style.apply.indexOf(type)!==-1 && style.svg !== value) {
                    if((style.svgAttr === "stroke" || style.svgAttr === "fill") && value.indexOf("rgba") !== -1) {
                        //separate alpha value, since illustrator can't handle it
                        regex = /rgba\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d?\.?\d*)\s*\)/gi;
                        matches = regex.exec(value);
                        this.__currentElement.setAttribute(style.svgAttr, format("rgb({r},{g},{b})", {r:matches[1], g:matches[2], b:matches[3]}));
                        this.__currentElement.setAttribute(style.svgAttr+"-opacity", matches[4]);
                    } else {
                        //otherwise only update attribute if right type, and not svg default
                        this.__currentElement.setAttribute(style.svgAttr, value);
                    }
                }
            }
        }

    };

    /**
     * Will return the closest group or svg node. May return the current element.
     * @private
     */
    ctx.prototype.__closestGroupOrSvg = function(node) {
        node = node || this.__currentElement;
        if(node.nodeName === "g" || node.nodeName === "svg") {
            return node;
        } else {
            return this.__closestGroupOrSvg(node.parentNode);
        }
    };

    /**
     * Returns the serialized value of the svg so far
     * @param fixNamedEntities - Standalone SVG doesn't support named entities, which document.createTextNode encodes.
     *                           If true, we attempt to find all named entities and encode it as a numeric entity.
     * @return serialized svg
     */
    ctx.prototype.getSerializedSvg = function(fixNamedEntities) {
        var serialized = new XMLSerializer().serializeToString(this.__root),
            keys, i, key, value, regexp, xmlns;

        //IE search for a duplicate xmnls because they didn't implement setAttributeNS correctly
        xmlns = /xmlns="http:\/\/www\.w3\.org\/2000\/svg".+xmlns="http:\/\/www\.w3\.org\/2000\/svg/gi;
        if(xmlns.test(serialized)) {
            serialized = serialized.replace('xmlns="http://www.w3.org/2000/svg','xmlns:xlink="http://www.w3.org/1999/xlink');
        }

        if(fixNamedEntities) {
            keys = Object.keys(namedEntities);
            //loop over each named entity and replace with the proper equivalent.
            for(i=0; i<keys.length; i++) {
                key = keys[i];
                value = namedEntities[key];
                regexp = new RegExp(key, "gi");
                if(regexp.test(serialized)) {
                    serialized = serialized.replace(regexp, value);
                }
            }
        }

        return serialized;
    };


    /**
     * Returns the root svg
     * @return
     */
    ctx.prototype.getSvg = function() {
        return this.__root;
    };
    /**
     * Will generate a group tag.
     */
    ctx.prototype.save = function() {
        var group = createElement("g"), parent = this.__closestGroupOrSvg();
        this.__groupStack.push(parent);
        parent.appendChild(group);
        this.__currentElement = group;
        this.__stack.push(this.__getStyleState());
    };
    /**
     * Sets current element to parent, or just root if already root
     */
    ctx.prototype.restore = function(){
        this.__currentElement = this.__groupStack.pop();
        var state = this.__stack.pop();
        this.__applyStyleState(state);

    };

    /**
     * Helper method to add transform
     * @private
     */
    ctx.prototype.__addTransform = function(t) {

        //if the current element has siblings, add another group
        var parent = this.__closestGroupOrSvg();
        if(parent.childNodes.length > 0) {
            var group = createElement("g");
            parent.appendChild(group);
            this.__currentElement = group;
        }

        var transform = this.__currentElement.getAttribute("transform");
        if(transform) {
            transform += " ";
        } else {
            transform = "";
        }
        transform += t;
        this.__currentElement.setAttribute("transform", transform);
    };

    /**
     *  scales the current element
     */
    ctx.prototype.scale = function(x, y) {
        if(y === undefined) {
            y = x;
        }
        this.__addTransform(format("scale({x},{y})", {x:x, y:y}));
    };

    /**
     * rotates the current element
     */
    ctx.prototype.rotate = function(angle){
        var degrees = (angle * 180 / Math.PI);
        this.__addTransform(format("rotate({angle},{cx},{cy})", {angle:degrees, cx:0, cy:0}));
    };

    /**
     * translates the current element
     */
    ctx.prototype.translate = function(x, y){
        this.__addTransform(format("translate({x},{y})", {x:x,y:y}));
    };

    /**
     * applies a transform to the current element
     */
    ctx.prototype.transform = function(a, b, c, d, e, f){
        this.__addTransform(format("matrix({a},{b},{c},{d},{e},{f})", {a:a, b:b, c:c, d:d, e:e, f:f}));
    };

    /**
     * Create a new Path Element
     */
    ctx.prototype.beginPath = function(){
        var path, parent;

        // Note that there is only one current default path, it is not part of the drawing state.
        // See also: https://html.spec.whatwg.org/multipage/scripting.html#current-default-path
        this.__currentDefaultPath = "";
        this.__currentPosition = {};

        path = createElement("path", {}, true);
        parent = this.__closestGroupOrSvg();
        parent.appendChild(path);
        this.__currentElement = path;
    };

    /**
     * Helper function to apply currentDefaultPath to current path element
     * @private
     */
    ctx.prototype.__applyCurrentDefaultPath = function() {
        if(this.__currentElement.nodeName === "path") {
            var d = this.__currentDefaultPath;
            this.__currentElement.setAttribute("d", d);
        } else {
            throw new Error("Attempted to apply path command to node " + this.__currentElement.nodeName);
        }
    };

    /**
     * Helper function to add path command
     * @private
     */
    ctx.prototype.__addPathCommand = function(command){
        this.__currentDefaultPath += " ";
        this.__currentDefaultPath += command;
    };

    /**
     * Adds the move command to the current path element,
     * if the currentPathElement is not empty create a new path element
     */
    ctx.prototype.moveTo = function(x,y){
        if(this.__currentElement.nodeName !== "path") {
            this.beginPath();
        }

        // creates a new subpath with the given point
        this.__currentPosition = {x: x, y: y};
        this.__addPathCommand(format("M {x} {y}", {x:x, y:y}));
    };

    /**
     * Closes the current path
     */
    ctx.prototype.closePath = function(){
        this.__addPathCommand("Z");
    };

    /**
     * Adds a line to command
     */
    ctx.prototype.lineTo = function(x, y){
        this.__currentPosition = {x: x, y: y};
        if (this.__currentDefaultPath.indexOf('M') > -1) {
            this.__addPathCommand(format("L {x} {y}", {x:x, y:y}));
        } else {
            this.__addPathCommand(format("M {x} {y}", {x:x, y:y}));
        }
    };

    /**
     * Add a bezier command
     */
    ctx.prototype.bezierCurveTo = function(cp1x, cp1y, cp2x, cp2y, x, y) {
        this.__currentPosition = {x: x, y: y};
        this.__addPathCommand(format("C {cp1x} {cp1y} {cp2x} {cp2y} {x} {y}",
            {cp1x:cp1x, cp1y:cp1y, cp2x:cp2x, cp2y:cp2y, x:x, y:y}));
    };

    /**
     * Adds a quadratic curve to command
     */
    ctx.prototype.quadraticCurveTo = function(cpx, cpy, x, y){
        this.__currentPosition = {x: x, y: y};
        this.__addPathCommand(format("Q {cpx} {cpy} {x} {y}", {cpx:cpx, cpy:cpy, x:x, y:y}));
    };


    /**
     * Return a new normalized vector of given vector
     */
    var normalize = function(vector) {
        var len = Math.sqrt(vector[0] * vector[0] + vector[1] * vector[1]);
        return [vector[0] / len, vector[1] / len];
    };

    /**
     * Adds the arcTo to the current path
     *
     * @see http://www.w3.org/TR/2015/WD-2dcontext-20150514/#dom-context-2d-arcto
     */
    ctx.prototype.arcTo = function(x1, y1, x2, y2, radius) {
        // Let the point (x0, y0) be the last point in the subpath.
        var x0 = this.__currentPosition && this.__currentPosition.x;
        var y0 = this.__currentPosition && this.__currentPosition.y;

        // First ensure there is a subpath for (x1, y1).
        if (typeof x0 == "undefined" || typeof y0 == "undefined") {
            return;
        }

        // Negative values for radius must cause the implementation to throw an IndexSizeError exception.
        if (radius < 0) {
            throw new Error("IndexSizeError: The radius provided (" + radius + ") is negative.");
        }

        // If the point (x0, y0) is equal to the point (x1, y1),
        // or if the point (x1, y1) is equal to the point (x2, y2),
        // or if the radius radius is zero,
        // then the method must add the point (x1, y1) to the subpath,
        // and connect that point to the previous point (x0, y0) by a straight line.
        if (((x0 === x1) && (y0 === y1))
            || ((x1 === x2) && (y1 === y2))
            || (radius === 0)) {
            this.lineTo(x1, y1);
            return;
        }

        // Otherwise, if the points (x0, y0), (x1, y1), and (x2, y2) all lie on a single straight line,
        // then the method must add the point (x1, y1) to the subpath,
        // and connect that point to the previous point (x0, y0) by a straight line.
        var unit_vec_p1_p0 = normalize([x0 - x1, y0 - y1]);
        var unit_vec_p1_p2 = normalize([x2 - x1, y2 - y1]);
        if (unit_vec_p1_p0[0] * unit_vec_p1_p2[1] === unit_vec_p1_p0[1] * unit_vec_p1_p2[0]) {
            this.lineTo(x1, y1);
            return;
        }

        // Otherwise, let The Arc be the shortest arc given by circumference of the circle that has radius radius,
        // and that has one point tangent to the half-infinite line that crosses the point (x0, y0) and ends at the point (x1, y1),
        // and that has a different point tangent to the half-infinite line that ends at the point (x1, y1), and crosses the point (x2, y2).
        // The points at which this circle touches these two lines are called the start and end tangent points respectively.

        // note that both vectors are unit vectors, so the length is 1
        var cos = (unit_vec_p1_p0[0] * unit_vec_p1_p2[0] + unit_vec_p1_p0[1] * unit_vec_p1_p2[1]);
        var theta = Math.acos(Math.abs(cos));

        // Calculate origin
        var unit_vec_p1_origin = normalize([
            unit_vec_p1_p0[0] + unit_vec_p1_p2[0],
            unit_vec_p1_p0[1] + unit_vec_p1_p2[1]
        ]);
        var len_p1_origin = radius / Math.sin(theta / 2);
        var x = x1 + len_p1_origin * unit_vec_p1_origin[0];
        var y = y1 + len_p1_origin * unit_vec_p1_origin[1];

        // Calculate start angle and end angle
        // rotate 90deg clockwise (note that y axis points to its down)
        var unit_vec_origin_start_tangent = [
            -unit_vec_p1_p0[1],
            unit_vec_p1_p0[0]
        ];
        // rotate 90deg counter clockwise (note that y axis points to its down)
        var unit_vec_origin_end_tangent = [
            unit_vec_p1_p2[1],
            -unit_vec_p1_p2[0]
        ];
        var getAngle = function(vector) {
            // get angle (clockwise) between vector and (1, 0)
            var x = vector[0];
            var y = vector[1];
            if (y >= 0) { // note that y axis points to its down
                return Math.acos(x);
            } else {
                return -Math.acos(x);
            }
        };
        var startAngle = getAngle(unit_vec_origin_start_tangent);
        var endAngle = getAngle(unit_vec_origin_end_tangent);

        // Connect the point (x0, y0) to the start tangent point by a straight line
        this.lineTo(x + unit_vec_origin_start_tangent[0] * radius,
                    y + unit_vec_origin_start_tangent[1] * radius);

        // Connect the start tangent point to the end tangent point by arc
        // and adding the end tangent point to the subpath.
        this.arc(x, y, radius, startAngle, endAngle);
    };

    /**
     * Sets the stroke property on the current element
     */
    ctx.prototype.stroke = function(){
        if(this.__currentElement.nodeName === "path") {
            this.__currentElement.setAttribute("paint-order", "fill stroke markers");
        }
        this.__applyCurrentDefaultPath();
        this.__applyStyleToCurrentElement("stroke");
    };

    /**
     * Sets fill properties on the current element
     */
    ctx.prototype.fill = function(){
        if(this.__currentElement.nodeName === "path") {
            this.__currentElement.setAttribute("paint-order", "stroke fill markers");
        }
        this.__applyCurrentDefaultPath();
        this.__applyStyleToCurrentElement("fill");
    };

    /**
     *  Adds a rectangle to the path.
     */
    ctx.prototype.rect = function(x, y, width, height){
        if(this.__currentElement.nodeName !== "path") {
            this.beginPath();
        }
        this.moveTo(x, y);
        this.lineTo(x+width, y);
        this.lineTo(x+width, y+height);
        this.lineTo(x, y+height);
        this.lineTo(x, y);
        this.closePath();
    };


    /**
     * adds a rectangle element
     */
    ctx.prototype.fillRect = function(x, y, width, height){
        var rect, parent;
        rect = createElement("rect", {
            x : x,
            y : y,
            width : width,
            height : height
        }, true);
        parent = this.__closestGroupOrSvg();
        parent.appendChild(rect);
        this.__currentElement = rect;
        this.__applyStyleToCurrentElement("fill");
    };

    /**
     * Draws a rectangle with no fill
     * @param x
     * @param y
     * @param width
     * @param height
     */
    ctx.prototype.strokeRect = function(x, y, width, height){
        var rect, parent;
        rect = createElement("rect", {
            x : x,
            y : y,
            width : width,
            height : height
        }, true);
        parent = this.__closestGroupOrSvg();
        parent.appendChild(rect);
        this.__currentElement = rect;
        this.__applyStyleToCurrentElement("stroke");
    };


    /**
     * "Clears" a canvas by just drawing a white rectangle in the current group.
     */
    ctx.prototype.clearRect = function(x, y, width, height) {
        var rect, parent = this.__closestGroupOrSvg();
        rect = createElement("rect", {
            x : x,
            y : y,
            width : width,
            height : height,
            fill : "#FFFFFF"
        }, true);
        parent.appendChild(rect);
    };

    /**
     * Adds a linear gradient to a defs tag.
     * Returns a canvas gradient object that has a reference to it's parent def
     */
    ctx.prototype.createLinearGradient = function(x1, y1, x2, y2){
        var grad = createElement("linearGradient", {
            id : randomString(this.__ids),
            x1 : x1+"px",
            x2 : x2+"px",
            y1 : y1+"px",
            y2 : y2+"px",
            "gradientUnits" : "userSpaceOnUse"
        }, false);
        this.__defs.appendChild(grad);
        return new CanvasGradient(grad);
    };

    /**
     * Adds a radial gradient to a defs tag.
     * Returns a canvas gradient object that has a reference to it's parent def
     */
    ctx.prototype.createRadialGradient = function(x0, y0, r0, x1, y1, r1){
        var grad = createElement("radialGradient", {
            id : randomString(this.__ids),
            cx : x1+"px",
            cy : y1+"px",
            r  : r1+"px",
            fx : x0+"px",
            fy : y0+"px",
            "gradientUnits" : "userSpaceOnUse"
        }, false);
        this.__defs.appendChild(grad);
        return new CanvasGradient(grad);

    };

    /**
     * Parses the font string and returns svg mapping
     * @private
     */
    ctx.prototype.__parseFont = function() {
        var regex = /^\s*(?=(?:(?:[-a-z]+\s*){0,2}(italic|oblique))?)(?=(?:(?:[-a-z]+\s*){0,2}(small-caps))?)(?=(?:(?:[-a-z]+\s*){0,2}(bold(?:er)?|lighter|[1-9]00))?)(?:(?:normal|\1|\2|\3)\s*){0,3}((?:xx?-)?(?:small|large)|medium|smaller|larger|[.\d]+(?:\%|in|[cem]m|ex|p[ctx]))(?:\s*\/\s*(normal|[.\d]+(?:\%|in|[cem]m|ex|p[ctx])))?\s*([-,\"\sa-z]+?)\s*$/i;
        var fontPart = regex.exec( this.font );
        var data = {
            style : fontPart[1] || 'normal',
            size : fontPart[4] || '10px',
            family : fontPart[6] || 'sans-serif',
            weight: fontPart[3] || 'normal',
            decoration : fontPart[2] || 'normal',
            href : null
        };

        //canvas doesn't support underline natively, but we can pass this attribute
        if(this.__fontUnderline === "underline") {
            data.decoration = "underline";
        }

        //canvas also doesn't support linking, but we can pass this as well
        if(this.__fontHref) {
            data.href = this.__fontHref;
        }

        return data;
    };

    /**
     * Helper to link text fragments
     * @param font
     * @param element
     * @return {*}
     * @private
     */
    ctx.prototype.__wrapTextLink = function(font, element) {
        if(font.href) {
            var a = createElement("a");
            a.setAttributeNS("http://www.w3.org/1999/xlink", "xlink:href", font.href);
            a.appendChild(element);
            return a;
        }
        return element;
    };

    /**
     * Fills or strokes text
     * @param text
     * @param x
     * @param y
     * @param action - stroke or fill
     * @private
     */
    ctx.prototype.__applyText = function(text, x, y, action) {
        var font = this.__parseFont(),
            parent = this.__closestGroupOrSvg(),
            textElement = createElement("text", {
                "font-family" : font.family,
                "font-size" : font.size,
                "font-style" : font.style,
                "font-weight" : font.weight,
                "text-decoration" : font.decoration,
                "x" : x,
                "y" : y,
                "text-anchor": getTextAnchor(this.textAlign),
                "dominant-baseline": getDominantBaseline(this.textBaseline)
            }, true);

        textElement.appendChild(document.createTextNode(text));
        this.__currentElement = textElement;
        this.__applyStyleToCurrentElement(action);
        parent.appendChild(this.__wrapTextLink(font,textElement));
    };

    /**
     * Creates a text element
     * @param text
     * @param x
     * @param y
     */
    ctx.prototype.fillText = function(text, x, y){
        this.__applyText(text, x, y, "fill");
    };

    /**
     * Strokes text
     * @param text
     * @param x
     * @param y
     */
    ctx.prototype.strokeText = function(text, x, y){
        this.__applyText(text, x, y, "stroke");
    };

    /**
     * No need to implement this for svg.
     * @param text
     * @return {TextMetrics}
     */
    ctx.prototype.measureText = function(text){
        this.__ctx.font = this.font;
        return this.__ctx.measureText(text);
    };

    /**
     *  Arc command!
     */
    ctx.prototype.arc = function(x, y, radius, startAngle, endAngle, counterClockwise) {
        startAngle = startAngle % (2*Math.PI);
        endAngle = endAngle % (2*Math.PI);
        if(startAngle === endAngle) {
            //circle time! subtract some of the angle so svg is happy (svg elliptical arc can't draw a full circle)
            endAngle = ((endAngle + (2*Math.PI)) - 0.001 * (counterClockwise ? -1 : 1)) % (2*Math.PI);
        }
        var endX = x+radius*Math.cos(endAngle),
            endY = y+radius*Math.sin(endAngle),
            startX = x+radius*Math.cos(startAngle),
            startY = y+radius*Math.sin(startAngle),
            sweepFlag = counterClockwise ? 0 : 1,
            largeArcFlag = 0,
            diff = endAngle - startAngle;

        // https://github.com/gliffy/canvas2svg/issues/4
        if(diff < 0) {
            diff += 2*Math.PI;
        }

        if(counterClockwise) {
            largeArcFlag = diff > Math.PI ? 0 : 1;
        } else {
            largeArcFlag = diff > Math.PI ? 1 : 0;
        }

        this.lineTo(startX, startY);
        this.__addPathCommand(format("A {rx} {ry} {xAxisRotation} {largeArcFlag} {sweepFlag} {endX} {endY}",
            {rx:radius, ry:radius, xAxisRotation:0, largeArcFlag:largeArcFlag, sweepFlag:sweepFlag, endX:endX, endY:endY}));

        this.__currentPosition = {x: endX, y: endY};
    };

    /**
     * Generates a ClipPath from the clip command.
     */
    ctx.prototype.clip = function(){
        var group = this.__closestGroupOrSvg(),
            clipPath = createElement("clipPath"),
            id =  randomString(this.__ids),
            newGroup = createElement("g");

        group.removeChild(this.__currentElement);
        clipPath.setAttribute("id", id);
        clipPath.appendChild(this.__currentElement);

        this.__defs.appendChild(clipPath);

        //set the clip path to this group
        group.setAttribute("clip-path", format("url(#{id})", {id:id}));

        //clip paths can be scaled and transformed, we need to add another wrapper group to avoid later transformations
        // to this path
        group.appendChild(newGroup);

        this.__currentElement = newGroup;

    };

    /**
     * Draws a canvas, image or mock context to this canvas.
     * Note that all svg dom manipulation uses node.childNodes rather than node.children for IE support.
     * http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-drawimage
     */
    ctx.prototype.drawImage = function(){
        //convert arguments to a real array
        var args = Array.prototype.slice.call(arguments),
            image=args[0],
            dx, dy, dw, dh, sx=0, sy=0, sw, sh, parent, svg, defs, group,
            currentElement, svgImage, canvas, context, id;

        if(args.length === 3) {
            dx = args[1];
            dy = args[2];
            sw = image.width;
            sh = image.height;
            dw = sw;
            dh = sh;
        } else if(args.length === 5) {
            dx = args[1];
            dy = args[2];
            dw = args[3];
            dh = args[4];
            sw = image.width;
            sh = image.height;
        } else if(args.length === 9) {
            sx = args[1];
            sy = args[2];
            sw = args[3];
            sh = args[4];
            dx = args[5];
            dy = args[6];
            dw = args[7];
            dh = args[8];
        } else {
            throw new Error("Inavlid number of arguments passed to drawImage: " + arguments.length);
        }

        parent = this.__closestGroupOrSvg();
        currentElement = this.__currentElement;

        if(image instanceof ctx) {
            //canvas2svg mock canvas context. In the future we may want to clone nodes instead.
            //also I'm currently ignoring dw, dh, sw, sh, sx, sy for a mock context.
            svg = image.getSvg();
            defs = svg.childNodes[0];
            while(defs.childNodes.length) {
                id = defs.childNodes[0].getAttribute("id");
                this.__ids[id] = id;
                this.__defs.appendChild(defs.childNodes[0]);
            }
            group = svg.childNodes[1];
            parent.appendChild(group);
            this.__currentElement = group;
            this.translate(dx, dy);
            this.__currentElement = currentElement;
        } else if(image.nodeName === "CANVAS" || image.nodeName === "IMG") {
            //canvas or image
            svgImage = createElement("image");
            svgImage.setAttribute("width", dw);
            svgImage.setAttribute("height", dh);
            svgImage.setAttribute("preserveAspectRatio", "none");

            if(sx || sy || sw !== image.width || sh !== image.height) {
                //crop the image using a temporary canvas
                canvas = document.createElement("canvas");
                canvas.width = dw;
                canvas.height = dh;
                context = canvas.getContext("2d");
                context.drawImage(image, sx, sy, sw, sh, 0, 0, dw, dh);
                image = canvas;
            }

            svgImage.setAttributeNS("http://www.w3.org/1999/xlink", "xlink:href",
                image.nodeName === "CANVAS" ? image.toDataURL() : image.getAttribute("src"));
            parent.appendChild(svgImage);
            this.__currentElement = svgImage;
            this.translate(dx, dy);
            this.__currentElement = currentElement;
        }
    };

    /**
     * Generates a pattern tag
     */
    ctx.prototype.createPattern = function(image, repetition){
        var pattern = document.createElementNS("http://www.w3.org/2000/svg", "pattern"), id = randomString(this.__ids),
            img;
        pattern.setAttribute("id", id);
        pattern.setAttribute("width", image.width);
        pattern.setAttribute("height", image.height);
        if(image.nodeName === "CANVAS" || image.nodeName === "IMG") {
            img = document.createElementNS("http://www.w3.org/2000/svg", "image");
            img.setAttribute("width", image.width);
            img.setAttribute("height", image.height);
            img.setAttributeNS("http://www.w3.org/1999/xlink", "xlink:href",
                image.nodeName === "CANVAS" ? image.toDataURL() : image.getAttribute("src"));
            pattern.appendChild(img);
            this.__defs.appendChild(pattern);
        } else if(image instanceof ctx) {
            pattern.appendChild(image.__root.childNodes[1]);
            this.__defs.appendChild(pattern);
        }
        return new CanvasPattern(pattern, this);
    };

    /**
     * Not yet implemented
     */
    ctx.prototype.drawFocusRing = function(){};
    ctx.prototype.createImageData = function(){};
    ctx.prototype.getImageData = function(){};
    ctx.prototype.putImageData = function(){};
    ctx.prototype.globalCompositeOperation = function(){};
    ctx.prototype.setTransform = function(){};

    //add options for alternative namespace
    window.C2S = ctx;

}());