context.js

/*!!
 *  SVGCanvas v2.0.3
 *  Draw on SVG using Canvas's 2D Context API.
 *
 *  Licensed under the MIT license:
 *  http://www.opensource.org/licenses/mit-license.php
 *
 *  Author:
 *  Kerry Liu
 *  Zeno Zeng
 *
 *  Copyright (c) 2014 Gliffy Inc.
 *  Copyright (c) 2021 Zeno Zeng
 */

import * as utils from './utils';
import imageUtils from './image';

export default (function () {
    "use strict";

    var STYLES, Context, 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;
    }

    // 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"
        },
        "lineDash" : {
            svgAttr : "stroke-dasharray",
            canvas : [],
            svg : null,
            apply : "stroke"
        }
    };

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

    /**
     * Adds a color stop to the gradient root
     */
    CanvasGradient.prototype.addColorStop = function (offset, color) {
        var stop = this.__ctx.__createElement("stop"), regex, matches;
        stop.setAttribute("offset", offset);
        if (utils.toString(color).indexOf("rgba") !== -1) {
            //separate alpha value, since webkit can't handle it
            regex = /rgba\(\s*(\d*\.?\d+)\s*,\s*(\d*\.?\d+)\s*,\s*(\d*\.?\d+)\s*,\s*(\d?\.?\d*)\s*\)/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", utils.toString(color));
        }
        this.__root.appendChild(stop);
    };

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

    /**
     * The mock canvas context
     * @param o - options include:
     * ctx - existing Context2D to wrap around
     * 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)
     * document - the document object (defaults to the current document)
     */
    Context = function (o) {

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

        // keep support for this way of calling Context: new Context(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 Context)) {
            //did someone call this without new?
            return new Context(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.__document = options.document || document;

        // allow passing in an existing context to wrap around
        // if a context is passed in, we know a canvas already exist
        if (options.ctx) {
            this.__ctx = options.ctx;
        } else {
            this.__canvas = this.__document.createElement("canvas");
            this.__ctx = this.__canvas.getContext("2d");
        }

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

        //the root svg element
        this.__root = this.__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 = this.__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 = this.__document.createElementNS("http://www.w3.org/2000/svg", "g");
        this.__root.appendChild(this.__currentElement);

        // init transformation matrix
        this.resetTransform();

        this.__options = options;
        this.__id = Math.random().toString(16).substring(2, 8);
        this.__debug(`new`, o);
    };

    /**
     * Log
     *
     * @private
     */
    Context.prototype.__debug = function(...data) {
        if (!this.__options.debug) {
            return
        }
        console.debug(`svgcanvas#${this.__id}:`, ...data)
    }

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

        var element = this.__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;
    };

    /**
     * Applies default canvas styles to the context
     * @private
     */
    Context.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
     */
    Context.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
     */
    Context.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;
    };

    /**
     * @see https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/transform
     */
    Context.prototype.__applyTransformation = function (element, matrix) {
        const {a, b, c, d, e, f} = matrix || this.getTransform();
        element.setAttribute('transform', `matrix(${a} ${b} ${c} ${d} ${e} ${f})`)
    }

    /**
     * Apples the current styles to the current SVG element. On "ctx.fill" or "ctx.stroke"
     * @param type
     * @private
     */
    Context.prototype.__applyStyleToCurrentElement = function (type) {
        var currentElement = this.__currentElement;
        var currentStyleGroup = this.__currentElementsToStyle;
        if (currentStyleGroup) {
            currentElement.setAttribute(type, "");
            currentElement = currentStyleGroup.element;
            currentStyleGroup.children.forEach(function (node) {
                node.setAttribute(type, "");
            })
        }

        var keys = Object.keys(STYLES), i, style, value, regex, matches, id, nodeIndex, node;
        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 (value instanceof CanvasPattern) {
                    //pattern
                    if (value.__ctx) {
                        //copy over defs
                        for(nodeIndex = 0; nodeIndex < value.__ctx.__defs.childNodes.length; nodeIndex++){
                          node = value.__ctx.__defs.childNodes[nodeIndex];
                          id = node.getAttribute("id");
                          this.__ids[id] = id;
                          this.__defs.appendChild(node);
                        }
                    }
                    currentElement.setAttribute(style.apply, format("url(#{id})", {id:value.__root.getAttribute("id")}));
                }
                else if (value instanceof CanvasGradient) {
                    //gradient
                    currentElement.setAttribute(style.apply, 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 && value.indexOf("rgba") !== -1) {
                        //separate alpha value, since illustrator can't handle it
                        regex = /rgba\(\s*(\d*\.?\d+)\s*,\s*(\d*\.?\d+)\s*,\s*(\d*\.?\d+)\s*,\s*(\d?\.?\d*)\s*\)/gi;
                        matches = regex.exec(value);
                        currentElement.setAttribute(style.svgAttr, format("rgb({r},{g},{b})", {r:matches[1], g:matches[2], b:matches[3]}));
                        //should take globalAlpha here
                        var opacity = matches[4];
                        var globalAlpha = this.globalAlpha;
                        if (globalAlpha != null) {
                            opacity *= globalAlpha;
                        }
                        currentElement.setAttribute(style.svgAttr+"-opacity", opacity);
                    } else {
                        var attr = style.svgAttr;
                        if (keys[i] === 'globalAlpha') {
                            attr = type+'-'+style.svgAttr;
                            if (currentElement.getAttribute(attr)) {
                                 //fill-opacity or stroke-opacity has already been set by stroke or fill.
                                continue;
                            }
                        } else if (keys[i] === 'lineWidth') {
                            var scale = this.__getTransformScale();
                            value = value * Math.max(scale.x, scale.y);
                        }
                        //otherwise only update attribute if right type, and not svg default
                        currentElement.setAttribute(attr, value);
                    }
                }
            }
        }
    };

    /**
     * Will return the closest group or svg node. May return the current element.
     * @private
     */
    Context.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
     */
    Context.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
     */
    Context.prototype.getSvg = function () {
        return this.__root;
    };

    /**
     * Will generate a group tag.
     */
    Context.prototype.save = function () {
        var group = this.__createElement("g");
        var parent = this.__closestGroupOrSvg();
        this.__groupStack.push(parent);
        parent.appendChild(group);
        this.__currentElement = group;
        const style = this.__getStyleState();

        this.__debug('save style', style)
        this.__styleStack.push(style);
        if (!this.__transformMatrixStack) {
            this.__transformMatrixStack = [];
        }
        this.__transformMatrixStack.push(this.getTransform());
    };

    /**
     * Sets current element to parent, or just root if already root
     */
    Context.prototype.restore = function () {
        this.__currentElement = this.__groupStack.pop();
        this.__currentElementsToStyle = null;
        //Clearing canvas will make the poped group invalid, currentElement is set to the root group node.
        if (!this.__currentElement) {
            this.__currentElement = this.__root.childNodes[1];
        }
        var state = this.__styleStack.pop();
        this.__debug('restore style', state);
        this.__applyStyleState(state);
        if (this.__transformMatrixStack && this.__transformMatrixStack.length > 0) {
            this.setTransform(this.__transformMatrixStack.pop())
        }

    };

    /**
     * Create a new Path Element
     */
    Context.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 = this.__createElement("path", {}, true);
        parent = this.__closestGroupOrSvg();
        parent.appendChild(path);
        this.__currentElement = path;
    };

    /**
     * Helper function to apply currentDefaultPath to current path element
     * @private
     */
    Context.prototype.__applyCurrentDefaultPath = function () {
        var currentElement = this.__currentElement;
        if (currentElement.nodeName === "path") {
            currentElement.setAttribute("d", this.__currentDefaultPath);
        } else {
            console.error("Attempted to apply path command to node", currentElement.nodeName);
        }
    };

    /**
     * Helper function to add path command
     * @private
     */
    Context.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
     */
    Context.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: this.__matrixTransform(x, y).x,
            y: this.__matrixTransform(x, y).y
        }));
    };

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

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

    /**
     * Add a bezier command
     */
    Context.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: this.__matrixTransform(cp1x, cp1y).x,
                cp1y: this.__matrixTransform(cp1x, cp1y).y,
                cp2x: this.__matrixTransform(cp2x, cp2y).x,
                cp2y: this.__matrixTransform(cp2x, cp2y).y,
                x: this.__matrixTransform(x, y).x,
                y: this.__matrixTransform(x, y).y
            }));
    };

    /**
     * Adds a quadratic curve to command
     */
    Context.prototype.quadraticCurveTo = function (cpx, cpy, x, y) {
        this.__currentPosition = {x: x, y: y};
        this.__addPathCommand(format("Q {cpx} {cpy} {x} {y}", {
            cpx: this.__matrixTransform(cpx, cpy).x,
            cpy: this.__matrixTransform(cpx, cpy).y,
            x: this.__matrixTransform(x, y).x,
            y: this.__matrixTransform(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
     */
    Context.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
     */
    Context.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
     */
    Context.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.
     */
    Context.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 to the path.
     * https://github.com/processing/p5.js/commit/a975515e9ea0a43d89ed522f281d8c9433ede96c
     */
    Context.prototype.roundRect = function (x, y, w, h, radii) {
        if (this.__currentElement.nodeName !== "path") {
            this.beginPath();
        }
        let tl, tr, br, bl;
        if (typeof radii == 'number') {
            tl = radii;
            tr = radii;
            br = radii;
            bl = radii;
        } else {
            [tl, tr, br, bl] = radii;
        }
        this.moveTo(x + tl, y);
        this.arcTo(x + w, y, x + w, y + h, tr);
        this.arcTo(x + w, y + h, x, y + h, br);
        this.arcTo(x, y + h, x, y, bl);
        this.arcTo(x, y, x + w, y, tl);
        this.closePath();
    };

    /**
     * adds a rectangle element
     */
    Context.prototype.fillRect = function (x, y, width, height) {
        let {a, b, c, d, e, f} = this.getTransform();
        if (JSON.stringify([a, b, c, d, e, f]) === JSON.stringify([1, 0, 0, 1, 0, 0])) {
            //clear entire canvas
            if (x === 0 && y === 0 && width === this.width && height === this.height) {
                this.__clearCanvas();
            }
        }
        var rect, parent;
        rect = this.__createElement("rect", {
            x : x,
            y : y,
            width : width,
            height : height
        }, true);
        parent = this.__closestGroupOrSvg();
        parent.appendChild(rect);
        this.__currentElement = rect;
        this.__applyTransformation(rect);
        this.__applyStyleToCurrentElement("fill");
    };

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


    /**
     * Clear entire canvas:
     * 1. save current transforms
     * 2. remove all the childNodes of the root g element
     */
    Context.prototype.__clearCanvas = function () {
        var rootGroup = this.__root.childNodes[1];
        this.__root.removeChild(rootGroup);
        this.__currentElement = this.__document.createElementNS("http://www.w3.org/2000/svg", "g");
        this.__root.appendChild(this.__currentElement);
        //reset __groupStack as all the child group nodes are all removed.
        this.__groupStack = [];
    };

    /**
     * "Clears" a canvas by just drawing a white rectangle in the current group.
     */
    Context.prototype.clearRect = function (x, y, width, height) {
        let {a, b, c, d, e, f} = this.getTransform();
        if (JSON.stringify([a, b, c, d, e, f]) === JSON.stringify([1, 0, 0, 1, 0, 0])) {
            //clear entire canvas
            if (x === 0 && y === 0 && width === this.width && height === this.height) {
                this.__clearCanvas();
                return;
            }
        }
        var rect, parent = this.__closestGroupOrSvg();
        rect = this.__createElement("rect", {
            x : x,
            y : y,
            width : width,
            height : height,
            fill : "#FFFFFF"
        }, true);
        this.__applyTransformation(rect)
        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
     */
    Context.prototype.createLinearGradient = function (x1, y1, x2, y2) {
        var grad = this.__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, this);
    };

    /**
     * Adds a radial gradient to a defs tag.
     * Returns a canvas gradient object that has a reference to it's parent def
     */
    Context.prototype.createRadialGradient = function (x0, y0, r0, x1, y1, r1) {
        var grad = this.__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, this);

    };

    /**
     * Fills or strokes text
     * @param text
     * @param x
     * @param y
     * @param action - stroke or fill
     * @private
     */
    Context.prototype.__applyText = function (text, x, y, action) {
        var el = document.createElement("span");
        el.setAttribute("style", 'font:' + this.font);

        var style = el.style, // CSSStyleDeclaration object
            parent = this.__closestGroupOrSvg(),
            textElement = this.__createElement("text", {
                "font-family": style.fontFamily,
                "font-size": style.fontSize,
                "font-style": style.fontStyle,
                "font-weight": style.fontWeight,

                // canvas doesn't support underline natively, but we do :)
                "text-decoration": this.__fontUnderline,
                "x": x,
                "y": y,
                "text-anchor": getTextAnchor(this.textAlign),
                "dominant-baseline": getDominantBaseline(this.textBaseline)
            }, true);

        textElement.appendChild(this.__document.createTextNode(text));
        this.__currentElement = textElement;
        this.__applyTransformation(textElement);
        this.__applyStyleToCurrentElement(action);

        if (this.__fontHref) {
            var a = this.__createElement("a");
            // canvas doesn't natively support linking, but we do :)
            a.setAttributeNS("http://www.w3.org/1999/xlink", "xlink:href", this.__fontHref);
            a.appendChild(textElement);
            textElement = a;
        }

        parent.appendChild(textElement);
    };

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

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

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

    /**
     *  Arc command!
     */
    Context.prototype.arc = function (x, y, radius, startAngle, endAngle, counterClockwise) {
        // in canvas no circle is drawn if no angle is provided.
        if (startAngle === endAngle) {
            return;
        }
        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;
        }

        var scaleX = Math.hypot(this.__transformMatrix.a, this.__transformMatrix.b);
        var scaleY = Math.hypot(this.__transformMatrix.c, this.__transformMatrix.d);

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

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

    /**
     *  Ellipse command!
     */
     Context.prototype.ellipse = function(x, y, radiusX, radiusY, rotation, startAngle, endAngle, counterClockwise) {
        if (startAngle === endAngle) {
            return;
        }

        var transformedCenter = this.__matrixTransform(x, y);
        x = transformedCenter.x;
        y = transformedCenter.y;
        var scale = this.__getTransformScale();
        radiusX = radiusX * scale.x;
        radiusY = radiusY * scale.y;
        rotation = rotation + this.__getTransformRotation()

        startAngle = startAngle % (2*Math.PI);
        endAngle = endAngle % (2*Math.PI);
        if(startAngle === endAngle) {
            endAngle = ((endAngle + (2*Math.PI)) - 0.001 * (counterClockwise ? -1 : 1)) % (2*Math.PI);
        }
        var endX = x + Math.cos(-rotation) * radiusX * Math.cos(endAngle)
                     + Math.sin(-rotation) * radiusY * Math.sin(endAngle),
            endY = y - Math.sin(-rotation) * radiusX * Math.cos(endAngle)
                     + Math.cos(-rotation) * radiusY * Math.sin(endAngle),
            startX = x + Math.cos(-rotation) * radiusX * Math.cos(startAngle)
                       + Math.sin(-rotation) * radiusY * Math.sin(startAngle),
            startY = y - Math.sin(-rotation) * radiusX * Math.cos(startAngle)
                       + Math.cos(-rotation) * radiusY * Math.sin(startAngle),
            sweepFlag = counterClockwise ? 0 : 1,
            largeArcFlag = 0,
            diff = endAngle - startAngle;

        if(diff < 0) {
            diff += 2*Math.PI;
        }

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

        // Transform is already applied, so temporarily remove since lineTo
        // will apply it again.
        var currentTransform = this.__transformMatrix;
        this.resetTransform();
        this.lineTo(startX, startY);
        this.__transformMatrix = currentTransform;

        this.__addPathCommand(format("A {rx} {ry} {xAxisRotation} {largeArcFlag} {sweepFlag} {endX} {endY}",
            {
                rx:radiusX, 
                ry:radiusY, 
                xAxisRotation:rotation*(180/Math.PI), 
                largeArcFlag:largeArcFlag, 
                sweepFlag:sweepFlag, 
                endX:endX,
                endY:endY
            }));

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

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

        this.__applyCurrentDefaultPath();
        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
     */
    Context.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("Invalid number of arguments passed to drawImage: " + arguments.length);
        }

        parent = this.__closestGroupOrSvg();
        currentElement = this.__currentElement;
        const matrix = this.getTransform().translate(dx, dy);
        if (image instanceof Context) {
            //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().cloneNode(true);
            if (svg.childNodes && svg.childNodes.length > 1) {
                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];
                if (group) {
                    this.__applyTransformation(group, matrix);
                    parent.appendChild(group);
                }
            }
        } else if (image.nodeName === "CANVAS" || image.nodeName === "IMG") {
            //canvas or image
            svgImage = this.__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 = this.__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;
            }
            this.__applyTransformation(svgImage, matrix);
            svgImage.setAttributeNS("http://www.w3.org/1999/xlink", "xlink:href",
                image.nodeName === "CANVAS" ? image.toDataURL() : image.getAttribute("src"));
            parent.appendChild(svgImage);
        }
    };

    /**
     * Generates a pattern tag
     */
    Context.prototype.createPattern = function (image, repetition) {
        var pattern = this.__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);
        // We want the pattern sizing to be absolute, and not relative
        // https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Patterns
        // https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/patternUnits
        pattern.setAttribute("patternUnits", "userSpaceOnUse");

        if (image.nodeName === "CANVAS" || image.nodeName === "IMG") {
            img = this.__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 Context) {
            pattern.appendChild(image.__root.childNodes[1]);
            this.__defs.appendChild(pattern);
        }
        return new CanvasPattern(pattern, this);
    };

    Context.prototype.setLineDash = function (dashArray) {
        if (dashArray && dashArray.length > 0) {
            this.lineDash = dashArray.join(",");
        } else {
            this.lineDash = null;
        }
    };

    /**
     * SetTransform changes the current transformation matrix to
     * the matrix given by the arguments as described below.
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setTransform
     */
    Context.prototype.setTransform = function (a, b, c, d, e, f) {
        if (a instanceof DOMMatrix) {
            this.__transformMatrix = new DOMMatrix([a.a, a.b, a.c, a.d, a.e, a.f]);
        } else {
            this.__transformMatrix = new DOMMatrix([a, b, c, d, e, f]);
        }
    };

    /**
     * GetTransform Returns a copy of the current transformation matrix,
     * as a newly created DOMMAtrix Object
     *
     * @returns A DOMMatrix Object
     */
    Context.prototype.getTransform = function () {
        let {a, b, c, d, e, f} = this.__transformMatrix;
        return new DOMMatrix([a, b, c, d, e, f]);
    };

    /**
     * ResetTransform resets the current transformation matrix to the identity matrix
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/resetTransform
     */
    Context.prototype.resetTransform = function () {
        this.setTransform(1, 0, 0, 1, 0, 0);
    };

    /**
     * Add the scaling transformation described by the arguments to the current transformation matrix.
     *
     * @param x The x argument represents the scale factor in the horizontal direction
     * @param y The y argument represents the scale factor in the vertical direction.
     * @see https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-scale
     */
    Context.prototype.scale = function (x, y) {
        if (y === undefined) {
            y = x;
        }
        // If either of the arguments are infinite or NaN, then return.
        if (isNaN(x) || isNaN(y) || !isFinite(x) || !isFinite(y)) {
            return
        }
        let matrix = this.getTransform().scale(x, y);
        this.setTransform(matrix);
    };

    /**
     * Rotate adds a rotation to the transformation matrix.
     *
     * @param angle The rotation angle, clockwise in radians. You can use degree * Math.PI / 180 to calculate a radian from a degree.
     * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/rotate
     * @see https://www.w3.org/TR/css-transforms-1
     */
    Context.prototype.rotate = function (angle) {
        let matrix = this.getTransform().multiply(new DOMMatrix([
            Math.cos(angle),
            Math.sin(angle),
            -Math.sin(angle),
            Math.cos(angle),
            0,
            0
        ]))
        this.setTransform(matrix);
    };

    /**
     * Translate adds a translation transformation to the current matrix.
     *
     * @param x Distance to move in the horizontal direction. Positive values are to the right, and negative to the left.
     * @param y Distance to move in the vertical direction. Positive values are down, and negative are up.
     * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/translate
     */
    Context.prototype.translate = function (x, y) {
        const matrix = this.getTransform().translate(x, y);
        this.setTransform(matrix);
    };

    /**
     * Transform multiplies the current transformation with the matrix described by the arguments of this method.
     * This lets you scale, rotate, translate (move), and skew the context.
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/transform
     */
    Context.prototype.transform = function (a, b, c, d, e, f) {
        const matrix = this.getTransform().multiply(new DOMMatrix([a, b, c, d, e, f]));
        this.setTransform(matrix);
    };

    Context.prototype.__matrixTransform = function(x, y) {
        return new DOMPoint(x, y).matrixTransform(this.__transformMatrix)
    }

    /**
     * 
     * @returns The scale component of the transform matrix as {x,y}.
     */
    Context.prototype.__getTransformScale = function() {
        return {
            x: Math.hypot(this.__transformMatrix.a, this.__transformMatrix.b),
            y: Math.hypot(this.__transformMatrix.c, this.__transformMatrix.d)
        };
    }

    /**
     * 
     * @returns The rotation component of the transform matrix in radians.
     */
    Context.prototype.__getTransformRotation = function() {
        return Math.atan2(this.__transformMatrix.b, this.__transformMatrix.a);
    }

    /**
     *
     * @param {*} sx The x-axis coordinate of the top-left corner of the rectangle from which the ImageData will be extracted.
     * @param {*} sy The y-axis coordinate of the top-left corner of the rectangle from which the ImageData will be extracted.
     * @param {*} sw The width of the rectangle from which the ImageData will be extracted. Positive values are to the right, and negative to the left.
     * @param {*} sh The height of the rectangle from which the ImageData will be extracted. Positive values are down, and negative are up.
     * @param {Boolean} options.async Will return a Promise<ImageData> if true, must be set to true
     * @returns An ImageData object containing the image data for the rectangle of the canvas specified. The coordinates of the rectangle's top-left corner are (sx, sy), while the coordinates of the bottom corner are (sx + sw, sy + sh).
     */
    Context.prototype.getImageData = function(sx, sy, sw, sh, options) {
        return imageUtils.getImageData(this.getSvg(), this.width, this.height, sx, sy, sw, sh, options);
    };

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

    return Context;
}());