Fabric.js — Building a Canvas Library

Fabric.jsBulding a canvas library @kangax ✎ BK.js ✎ 2011

Who am I? @kangaxperfectionkills.com kangax.github.com/es5-compat-table/

fabric.js Fabric.js is a framework that makes it easy to work with HTML5 canvas element. It is an interactive object model on top of canvas element.It is also an SVG-to-canvas parser.

t ian Canvas? -co m pl WHATWG says:“The canvas element provides scripts with a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, or other visual images on the ﬂy.” http://www.whatwg.org/specs/web-apps/current-work/ multipage/the-canvas-element.html#the-canvas-element

CanvasCharts GamesEditors Physics simulation

How canvas works document.getElementById(‘canvas’).getContext(‘2d’) CanvasRenderingContext2D• clearRect() • arc()• fillRect() • drawImage() • createImageData() • arcTo()• strokeRect() • bezierCurveTo() • putImageData() • getImageData() • clip() • closePath()• restore() • fill()• save() • strokeText() • lineTo() • fillText() • moveTo()• rotate() • measureText() • quadraticCurveTo()• scale() • rect()• transform() • stroke()• translate() • strokeStyle= • fillStyle=

But why get rid of an elegant canvas API forsome questionable blob of Javascript code?

fabric vs. nativenative var canvasEl = document.getElementById(canvas); var ctx = canvasEl.getContext(2d); ctx.strokeStyle = ; ctx.fillStyle = red; ctx.fillRect(100, 100, 20, 20);fabric var canvas = new fabric.Element(canvas); var rect = new fabric.Rect({ top: 100, left: 100, fill: red, width: 20, height: 20 }); canvas.add(rect);

fabric vs. nativenative var canvasEl = document.getElementById(canvas); var ctx = canvasEl.getContext(2d); ctx.strokeStyle = ; ctx.fillStyle = red; because we all love radians ctx.save(); ctx.translate(100, 100); ctx.rotate(Math.PI / 180 * 45); ctx.fillRect(-10, -10, 20, 20); ctx.restore();fabric var canvas = new fabric.Element(canvas); var rect = new fabric.Rect({ top: 100, left: 100, fill: red, width: 20, height: 20, angle: 45 }); canvas.add(rect);

fabric vs. nativenative ctx.fillRect(20, 50, 20, 20);fabricrect.set(‘left’, 20).set(‘top’, 50);canvas.renderAll();

fabric vs. nativenative ctx.fillRect(20, 50, 20, 20); ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); ctx.fillRect(20, 50, 20, 20);fabricrect.set(‘left’, 20).set(‘top’, 50);canvas.renderAll();

But wait, there’s more! Object manipulations with mouse http://kangax.github.com/fabric.js/test/demo/

Goals• Unit tested (1000+ tests at the moment)• Modular (~20 small "classes")• Cross-browser (degrades gracefully)• Fast• Encapsulated in one object• No browser snifﬁng• ES5 strict mode -ready

Supported browsers• Firefox 2+• Safari 3+• Opera 9.64+• Chrome (all versions should work)• IE9 (IE7/8 via excanvas)

How fabric works “Hello world” examplevar canvas = new fabric.Element(canvas);var text = new fabric.Text(hello world, { fontfamily: delicious_500});canvas.add(text);

How fabric works “Hello world” examplevar canvas = new fabric.Element(canvas);var text = new fabric.Text(hello world, { fontfamily: delicious_500});canvas.add(text);text.setText(trololololo) .set(left, 100) .set(top, 100) .set(fontfamily, comic_sans);

How fabric works “Hello world” examplevar canvas = new fabric.Element(canvas);var text = new fabric.Text(hello world, { fontfamily: delicious_500});canvas.add(text);text.setText(trololololo) .set(left, 100) .set(top, 100) .set(fontfamily, comic_sans);canvas.remove(text);

How fabric works “Class” hierarchyfabric.Object fabric.util.* fabric.Elementfabric.Linefabric.Circlefabric.Triangle fabric.parseAttributesfabric.Ellipse fabric.parseElementsfabric.Rect fabric.parseStyleAttributefabric.Polyline fabric.parsePointsAttributefabric.Polygonfabric.Groupfabric.Textfabric.Image fabric.Colorfabric.Path fabric.PathGroup fabric.Point fabric.Intersection

How fabric works “Class” hierarchyfabric.Object clone cloneAsImage complexity getfabric.Line getCenterfabric.Circle getWidthfabric.Triangle getHeight intersectsWithObjectfabric.Ellipse isActivefabric.Rect isTypefabric.Polyline scale scaleToHeightfabric.Polygon scaleToWidthfabric.Group setfabric.Text setActive straightenfabric.Image toDataURLfabric.Path toJSON ...

How fabric works “Class” hierarchy clonefabric.Object cloneAsImage complexity get getCenterfabric.Line getRadiusXfabric.Circle getRadiusYfabric.Triangle getWidth getHeightfabric.Ellipse intersectsWithObjectfabric.Rect isActivefabric.Polyline isType scalefabric.Polygon scaleToHeightfabric.Group scaleToWidthfabric.Text set setActivefabric.Image straightenfabric.Path toDataURL toJSON ...

How fabric works “Class” hierarchy clonefabric.Object cloneAsImage complexity get getCenterfabric.Line getWidth getElementfabric.Circle getHeightfabric.Triangle intersectsWithObjectfabric.Ellipse isActive isTypefabric.Rect scalefabric.Polyline scaleToHeightfabric.Polygon scaleToWidth setfabric.Group setActivefabric.Text setElementfabric.Image straighten toDataURLfabric.Path toJSON toGrayscale ...

How fabric works fabric.Element add bringForwardfabric.Element bringToFront centerObjectH centerObjectV clear clone Main drawing area complexity containsPoint deactivateAll - Wraps <canvas> element getActiveObject - Renders fabric.* objects added to it getCenter - Provides mouse-based selection getHeight getWidth - Dispatches events getObjects insertAt isEmpty item loadFromJSON loadSVGFromURL remove renderAll ...

How fabric works fabric.Element render()fabric.Rect.prototype.render render() fabric.Path.prototype.render render() render() fabric.Image.prototype.render fabric.Circle.prototype.render

How fabric works Drawing a frame 1. clear entire canvas 2. for each object in canvas 2a. object.render() render() render()fabric.Rect.prototype.render fabric.Path.prototype.render render() render() fabric.Image.prototype.render fabric.Circle.prototype.render

How fabric works Prototypal inheritancefunction createClass() { var parent = null, based on properties = slice.call(arguments, 0); Prototype.js if (typeof properties[0] === function) { parent = properties.shift(); } function klass() { this.initialize.apply(this, arguments); } klass.superclass = parent; klass.subclasses = [ ]; if (parent) { subclass.prototype = parent.prototype; klass.prototype = new subclass; parent.subclasses.push(klass); } for (var i = 0, length = properties.length; i < length; i++) { addMethods(klass, properties[i]); } if (!klass.prototype.initialize) { klass.prototype.initialize = emptyFunction; } klass.prototype.constructor = klass; return klass;}

How fabric works Prototypal inheritancefabric.Path = fabric.util.createClass( fabric.Object, { type: path, initialize: function(path, options) { options = options || { }; ... }, render: function() { ... }, toString: function() { return #<fabric.Path ( + this.complexity() + ): + JSON.stringify({ top: this.top, left: this.left }) + >; }});

How fabric works SVG parser

How fabric works SVG parser<path d="M-122.304 84.285C-122.304 {84.285 -122.203 86.179 -123.027 path: [86.16C-123.851 86.141 -140.305 [ "M", -122.304, 84.285 ],38.066 -160.833 40.309C-160.833 [ "C", -122.304, 84.285,40.309 -143.05 32.956 -122.304 -122.203, 86.179,84.285z" /> -123.027, 86.16 ], [ "C", -123.851, ... ], [ ... ], ... ] }

How fabric works SVG parser { path: [ [ "M", -122.304, 84.285 ], [ "C", -122.304, 84.285, Instance of fabric.Path -122.203, 86.179,[[Prototype]] == fabric.Path.prototype -123.027, 86.16 ], [ "C", -123.851, ... ], [ ... ], ... ] }

How fabric works SVG parser fabric.Path.prototype.render (line 173)case C: // bezierCurveTo, absolute x = current[5]; { y = current[6]; path: [ controlX = current[3]; [ "M", -122.304, 84.285 ], controlY = current[4]; [ "C", -122.304, 84.285, ctx.bezierCurveTo( -122.203, 86.179, current[1] + l, current[2] + t, -123.027, 86.16 ], controlX + l, [ "C", -123.851, ... ], controlY + t, [ ... ], x + l, ... y + t ] ); } break;

How fabric works SVG parser Static fromElement method on all constructorsfabric.Line.fromElement = function(element, options) { var parsedAttributes = fabric.parseAttributes(element, fabric.Line.ATTRIBUTE_NAMES); var points = [ parsedAttributes.x1 || 0, parsedAttributes.y1 || 0, parsedAttributes.x2 || 0, parsedAttributes.y2 || 0 ]; return new fabric.Line(points, extend(parsedAttributes, options));};

How fabric works SVG parser Static fromElement method on all constructorsfabric.Path.fromElement = function(element, options) { var parsedAttributes = fabric.parseAttributes(element, fabric.Path.ATTRIBUTE_NAMES); return new fabric.Path(parsedAttributes.d, extend(parsedAttributes, options));}; Ditto for fabric.Rect, fabric.Circle, etc.

http://www.w3.org/TR/SVG/ paths.html#PathDataBNF Fun with SVG parsing

continued...

are we there yet?

Fun with SVG parsing

Docshttp://kangax.github.com/fabric.js/docs

Unit testshttp://kangax.github.com/fabric.js/test/unit/suite_runner

Benchmarks http://kangax.github.com/fabric.js/test/ raphael_vs_fabric/simple_shapeshttp://kangax.github.com/fabric.js/test/ raphael_vs_fabric/complex_shape

Future plans:• Smaller footprint (delete Cufon)• Custom builder• Better docs• More complete SVG parsing• toSVG()• Pretty website, logo (help!!111)• Better IE support

These slides online:http://slideshare.net/kangax

Thank you! Questions? http://spkr8.com/t/7303github.com/kangax/fabric.js@FabricJS Follow me @kangax

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Fabric.js — Building a Canvas Library

by Juriy Zaytsev on Apr 19, 2011

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