paper.js/src/canvas/CanvasProvider.js

/*
 * Paper.js - The Swiss Army Knife of Vector Graphics Scripting.
 * http://paperjs.org/
 *
 * Copyright (c) 2011 - 2013, Juerg Lehni & Jonathan Puckey
 * http://lehni.org/ & http://jonathanpuckey.com/
 *
 * Distributed under the MIT license. See LICENSE file for details.
 *
 * All rights reserved.
 */

// TODO: Run through the canvas array to find a canvas with the requested
// width / height, so we don't need to resize it?
var CanvasProvider = {
	canvases: [],

	getCanvas: function(width, height) {
		var size = height === undefined ? width : Size.create(width, height);
		if (this.canvases.length) {
			var canvas = this.canvases.pop();
			// If they are not the same size, we don't need to clear them
			// using clearRect and visa versa.
			if ((canvas.width != size.width)
					|| (canvas.height != size.height)) {
				canvas.width = size.width;
				canvas.height = size.height;
			} else {
				// +1 is needed on some browsers to really clear the borders
				canvas.getContext('2d').clearRect(0, 0,
						size.width + 1, size.height + 1);
			}
			return canvas;
		} else {
/*#*/ if (options.browser) {
			var canvas = document.createElement('canvas');
			canvas.width = size.width;
			canvas.height = size.height;
			return canvas;
/*#*/ } else { // !options.browser
			return new Canvas(size.width, size.height);
/*#*/ } // !options.browser
		}
	},

	getContext: function(width, height) {
		return this.getCanvas(width, height).getContext('2d');
	},

	 // release can receive either a canvas or a context.
	release: function(obj) {
		this.canvases.push(obj.canvas ? obj.canvas : obj);
	},
};