CanvasBlocker/lib/modifiedAPI.js

/* jslint moz: true, bitwise: true */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
(function(){
	"use strict";
	
	function getFakeCanvas(window, original){
		var context = window.HTMLCanvasElement.prototype.getContext.call(original, "2d");
		var imageData, data, source;
		if (context){
			imageData = window.CanvasRenderingContext2D.prototype.getImageData.call(context, 0, 0, original.width, original.height);
			source = imageData.data;
		}
		else {
			context = 
				window.HTMLCanvasElement.prototype.getContext.call(original, "webgl") ||
				window.HTMLCanvasElement.prototype.getContext.call(original, "experimental-webgl") ||
				window.HTMLCanvasElement.prototype.getContext.call(original, "webgl2") ||
				window.HTMLCanvasElement.prototype.getContext.call(original, "experimental-webgl2");
			imageData = new window.wrappedJSObject.ImageData(original.width, original.height);
			source = new window.wrappedJSObject.Uint8Array(imageData.data.length);
			window.WebGLRenderingContext.prototype.readPixels.call(
				context,
				0, 0, original.width, original.height,
				context.RGBA, context.UNSIGNED_BYTE,
				source
			);
		}
		data = imageData.data;
		
		for (var i = 0, l = data.length; i < l; i += 1){
			var value = source[i];
			if (value >= 0x80){
				value = value ^ Math.floor(Math.random() * 0x20);
			}
			else if (value >= 0x40){
				value = value ^ Math.floor(Math.random() * 0x10);
			}
			else if (value >= 0x20){
				value = value ^ Math.floor(Math.random() * 0x08);
			}
			else if (value >= 0x10){
				value = value ^ Math.floor(Math.random() * 0x04);
			}
			else if (value >= 0x08){
				value = value ^ Math.floor(Math.random() * 0x02);
			}
			else if (value >= 0x04){
				value = value ^ Math.floor(Math.random() * 0x01);
			}
			data[i] = value;
		}
		var canvas = original.cloneNode(true);
		context = window.HTMLCanvasElement.prototype.getContext.call(canvas, "2d");
		context.putImageData(imageData, 0, 0);
		return canvas;
	}
	function getWindow(canvas){
		return canvas.ownerDocument.defaultView;
	}
	// changed functions and their fakes
	exports.changedFunctions = {
		getContext: {
			type: "context",
			object: "HTMLCanvasElement"
		},
		toDataURL: {
			type: "readout",
			object: "HTMLCanvasElement",
			fake: function toDataURL(){
				var window = getWindow(this);
				return window.HTMLCanvasElement.prototype.toDataURL.apply(getFakeCanvas(window, this), arguments);
			}
		},
		toBlob: {
			type: "readout",
			object: "HTMLCanvasElement",
			fake: function toBlob(callback){
				var window = getWindow(this);
				return window.HTMLCanvasElement.prototype.toBlob.apply(getFakeCanvas(window, this), arguments);
			},
			exportOptions: {allowCallbacks: true}
		},
		mozGetAsFile: {
			type: "readout",
			object: "HTMLCanvasElement",
			mozGetAsFile: function mozGetAsFile(callbak){
				var window = getWindow(this);
				return window.HTMLCanvasElement.prototype.mozGetAsFile.apply(getFakeCanvas(window, this), arguments);
			}
		},
		getImageData: {
			type: "readout",
			object: "CanvasRenderingContext2D",
			fake: function getImageData(sx, sy, sw, sh){
				var window = getWindow(this.canvas);
				var context = window.HTMLCanvasElement.prototype.getContext.call(getFakeCanvas(window, this.canvas), "2d");
				var data = window.CanvasRenderingContext2D.prototype.getImageData.apply(context, arguments).data;
				
				var imageData = new window.wrappedJSObject.ImageData(sw, sh);
				for (var i = 0, l = data.length; i < l; i += 1){
					imageData.data[i] = data[i];
				}
				return imageData;
			}
		},
		readPixels: {
			type: "readout",
			object: "WebGLRenderingContext",
			fake: function readPixels(x, y, width, height, format, type, pixels){
				var window = getWindow(this.canvas);
				var context = window.HTMLCanvasElement.prototype.getContext.call(getFakeCanvas(window, this.canvas), "webGL");
				return window.WebGLRenderingContext.prototype.readPixels.apply(context, arguments);
				
			}
		}
	};
}());