node-easel/src/easeljs/filters/AlphaMapFilter.js

node wrapper for EaselJS, utilizing node-canvas.

/*
 * AlphaMapFilter
 * Visit http://createjs.com/ for documentation, updates and examples.
 *
 * Copyright (c) 2010 gskinner.com, inc.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

/**
 * @module EaselJS
 */

// namespace:
this.createjs = this.createjs || {};

(function () {
	"use strict";
	/**
	 * Applies a greyscale alpha map image (or canvas) to the target, such that the alpha channel of the result will
	 * be copied from the red channel of the map, and the RGB channels will be copied from the target.
	 *
	 * Generally, it is recommended that you use {{#crossLink "AlphaMaskFilter"}}{{/crossLink}}, because it has much
	 * better performance.
	 *
	 * <h4>Example</h4>
	 * This example draws a red->blue box, caches it, and then uses the cache canvas as an alpha map on a 100x100 image.
	 *
	 *       var box = new createjs.Shape();
	 *       box.graphics.beginLinearGradientFill(["#ff0000", "#0000ff"], [0, 1], 0, 0, 0, 100)
	 *       box.graphics.drawRect(0, 0, 100, 100);
	 *       box.cache(0, 0, 100, 100);
	 *
	 *       var bmp = new createjs.Bitmap("path/to/image.jpg");
	 *       bmp.filters = [
	 *           new createjs.AlphaMapFilter(box.cacheCanvas)
	 *       ];
	 *       bmp.cache(0, 0, 100, 100);
	 *       stage.addChild(bmp);
	 *
	 * See {{#crossLink "Filter"}}{{/crossLink}} for more information on applying filters.
	 * @class AlphaMapFilter
	 * @extends Filter
	 * @constructor
	 * @param {Image|HTMLCanvasElement} alphaMap The greyscale image (or canvas) to use as the alpha value for the
	 * result. This should be exactly the same dimensions as the target.
	 **/
	var AlphaMapFilter = function (alphaMap) {
		this.initialize(alphaMap);
	};
	var p = AlphaMapFilter.prototype = new createjs.Filter();

// constructor:
	/** @ignore */
	p.initialize = function (alphaMap) {
		this.alphaMap = alphaMap;
	};

// public properties:

	/**
	 * The greyscale image (or canvas) to use as the alpha value for the result. This should be exactly the same
	 * dimensions as the target.
	 * @property alphaMap
	 * @type Image|HTMLCanvasElement
	 **/
	p.alphaMap = null;

// private properties:
	p._alphaMap = null;
	p._mapData = null;

// public methods:

	p.applyFilter = function (ctx, x, y, width, height, targetCtx, targetX, targetY) {
		if (!this.alphaMap) {
			return true;
		}
		if (!this._prepAlphaMap()) {
			return false;
		}
		targetCtx = targetCtx || ctx;
		if (targetX == null) {
			targetX = x;
		}
		if (targetY == null) {
			targetY = y;
		}

		try {
			var imageData = ctx.getImageData(x, y, width, height);
		} catch (e) {
			//if (!this.suppressCrossDomainErrors) throw new Error("unable to access local image data: " + e);
			return false;
		}
		var data = imageData.data;
		var map = this._mapData;
		var l = data.length;
		for(var i = 0; i < l; i += 4) {
			data[i + 3] = map[i] || 0;
		}
		imageData.data = data;
		targetCtx.putImageData(imageData, targetX, targetY);
		return true;
	};

	/**
	 * Returns a clone of this object.
	 * @return {AlphaMapFilter} A clone of the current AlphaMapFilter instance.
	 **/
	p.clone = function () {
		return new AlphaMapFilter(this.alphaMap);
	};

	p.toString = function () {
		return "[AlphaMapFilter]";
	};

// private methods:
	p._prepAlphaMap = function () {
		if (!this.alphaMap) {
			return false;
		}
		if (this.alphaMap == this._alphaMap && this._mapData) {
			return true;
		}

		this._mapData = null;
		var map = this._alphaMap = this.alphaMap;
		var canvas = map;
		var ctx;
		if (map instanceof HTMLCanvasElement) {
			ctx = canvas.getContext("2d");
		} else {
			canvas = createjs.createCanvas ? createjs.createCanvas() : document.createElement("canvas");
			canvas.width = map.width;
			canvas.height = map.height;
			ctx = canvas.getContext("2d");
			ctx.drawImage(map, 0, 0);
		}

		try {
			var imgData = ctx.getImageData(0, 0, map.width, map.height);
		} catch (e) {
			//if (!this.suppressCrossDomainErrors) throw new Error("unable to access local image data: " + e);
			return false;
		}
		this._mapData = imgData.data;
		return true;
	};

	createjs.AlphaMapFilter = AlphaMapFilter;

}());