CanvasBlocker/lib/colorStatistics.js

/* 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";
	
	
	var scope;
	if ((typeof exports) !== "undefined"){
		scope = exports;
	}
	else {
		window.scope.colorStatistics = {};
		scope = window.scope.colorStatistics;
	}
	
	class Statistic{
		constructor(){
			this.colors = Object.create(null);
			this.numberOfColors = 0;
			
			this.minBoundary = {count: Number.NEGATIVE_INFINITY};
			this.maxBoundary = {count: Number.POSITIVE_INFINITY, previousColor: this.minBoundary};
			this.minBoundary.nextColor = this.maxBoundary;
		}
		addColor(r, g, b, a){
			var index = String.fromCharCode(r, g, b, a);
			var color = this.colors[index];
			if (!color){
				color = {
					index,
					color: [r, g, b, a],
					count: 0,
					previousColor: this.minBoundary,
					nextColor: this.minBoundary.nextColor
				};
				this.numberOfColors += 1;
				this.minBoundary.nextColor = color;
				color.nextColor.previousColor = color;
				this.colors[index] = color;
			}
			color.count += 1;
			if (color.count > color.nextColor.count){
				// swap colors to remain in right order
				// a_ -> b_ -> c -> d becomes a_ -> c -> b_ -> d
				var a_ = color.previousColor;
				var b_ = color;
				var c = color.nextColor;
				var d = color.nextColor.nextColor;
				
				a_.nextColor = c;
				c.previousColor = a_;
				
				c.nextColor = b_;
				b_.previousColor = c;
				
				b_.nextColor = d;
				d.previousColor = b_;
			}
		}
		getMaxColors(n){
			n = Math.min(n, this.numberOfColors);
			var colors = Object.create(null);
			var current = this.maxBoundary;
			for (;n && current;n -= 1){
				current = current.previousColor;
				colors[current.index] = current;
			}
			return colors;
		}
	}
	
	scope.compute = function computeColorStatistics(rawData){
		var statistic = new Statistic();
		for (var i = 0, l = rawData.length; i < l; i += 4){
			statistic.addColor(
				rawData[i + 0],
				rawData[i + 1],
				rawData[i + 2],
				rawData[i + 3]
			);
		}
		return statistic;
	};
	scope.hasMoreColors = function hasMoreColors(rawData, threshold, statistic){
		if (statistic){
			return statistic.numberOfColors > threshold;
		}
		else {
			var colors = Object.create(null);
			var count = 0;
			for (var i = 0, l = rawData.length; i < l; i += 4){
				var index = String.fromCharCode(
					rawData[i + 0],
					rawData[i + 1],
					rawData[i + 2],
					rawData[i + 3]
				);
				if (!Object.prototype.hasOwnProperty.call(colors, index)){
					colors[index] = true;
					count += 1;
					if (count > threshold){
						return true;
					}
				}
			}
			return count > threshold;
		}
	};
}());