@createjs/easeljs/src/filters/AlphaMaskFilter.js

The Easel JavaScript library provides a full, hierarchical display list, a core interaction model, and helper classes to make working with the HTML5 Canvas element much easier. Part of the CreateJS suite of libraries.

/**
 * @license AlphaMaskFilter
 * Visit http://createjs.com/ for documentation, updates and examples.
 *
 * Copyright (c) 2017 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.
 */

import Filter from "./Filter";

/**
 * Applies the alpha from the mask image (or canvas) to the target, such that the alpha channel of the result will
 * be derived from the mask, and the RGB channels will be copied from the target. This can be used, for example, to
 * apply an alpha mask to a display object. This can also be used to combine a JPG compressed RGB image with a PNG32
 * alpha mask, which can result in a much smaller file size than a single PNG32 containing ARGB.
 *
 * <b>IMPORTANT NOTE: This filter currently does not support the targetCtx, or targetX/Y parameters correctly.</b>
 *
 * @memberof easeljs
 * @extends easeljs.Filter
 * @example
 * var box = new Shape();
 * box.graphics.beginLinearGradientFill(["#000000", "rgba(0, 0, 0, 0)"], [0, 1], 0, 0, 100, 100)
 * box.graphics.drawRect(0, 0, 100, 100);
 * box.cache(0, 0, 100, 100);
 * var bmp = new Bitmap("path/to/image.jpg");
 * bmp.filters = [ new AlphaMaskFilter(box.cacheCanvas) ];
 * bmp.cache(0, 0, 100, 100);
 *
 * @param {HTMLImageElement | HTMLCanvasElement} mask
 */
export default class AlphaMaskFilter extends Filter {

	constructor (mask) {
		super();

		/**
		 * The image (or canvas) to use as the mask.
		 * @type {HTMLImageElement | HTMLCanvasElement}
		 */
		this.mask = mask;

		this.usesContext = true;

		this.FRAG_SHADER_BODY = `
			uniform sampler2D uAlphaSampler;

			void main (void) {
				vec4 color = texture2D(uSampler, vRenderCoord);
				vec4 alphaMap = texture2D(uAlphaSampler, vTextureCoord);

				gl_FragColor = vec4(color.rgb, color.a * alphaMap.a);
			}
		`;
	}

	/**
	 * Applies the filter to the specified context.
	 *
	 * <strong>IMPORTANT NOTE: This filter currently does not support the targetCtx, or targetX/Y parameters correctly.</strong>
	 * @param {CanvasRenderingContext2D} ctx The 2D context to use as the source.
	 * @param {Number} x The x position to use for the source rect.
	 * @param {Number} y The y position to use for the source rect.
	 * @param {Number} width The width to use for the source rect.
	 * @param {Number} height The height to use for the source rect.
	 * @param {CanvasRenderingContext2D} [targetCtx] NOT SUPPORTED IN THIS FILTER. The 2D context to draw the result to. Defaults to the context passed to ctx.
	 * @param {Number} [targetX] NOT SUPPORTED IN THIS FILTER. The x position to draw the result to. Defaults to the value passed to x.
	 * @param {Number} [targetY] NOT SUPPORTED IN THIS FILTER. The y position to draw the result to. Defaults to the value passed to y.
	 * @return {Boolean} If the filter was applied successfully.
	 */
	applyFilter (ctx, x, y, width, height, targetCtx, targetX, targetY) {
		if (!this.mask) { return true; }
		targetCtx = targetCtx || ctx;
		if (targetX == null) { targetX = x; }
		if (targetY == null) { targetY = y; }

		targetCtx.save();
		if (ctx != targetCtx) {
			// TODO: support targetCtx and targetX/Y
			// clearRect, then draw the ctx in?
			return false;
		}

		targetCtx.globalCompositeOperation = "destination-in";
		targetCtx.drawImage(this.mask, targetX, targetY);
		targetCtx.restore();
		return true;
	}

	/**
	 * @return {easeljs.AlphaMaskFilter}
	 */
	clone () {
		return new AlphaMaskFilter(this.mask);
	}

	/**
	 * @todo docs
	 * @param {*} gl
	 * @param {*} stage
	 * @param {*} shaderProgram
	 */
	shaderParamSetup (gl, stage, shaderProgram) {
		if(!this._mapTexture) { this._mapTexture = gl.createTexture(); }

		gl.activeTexture(gl.TEXTURE1);
		gl.bindTexture(gl.TEXTURE_2D, this._mapTexture);
		stage.setTextureParams(gl);
		gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, this.mask);

		gl.uniform1i(
			gl.getUniformLocation(shaderProgram, "uAlphaSampler"),
			1
		);
	}

}