[AS3] Animated GIF optimization – frame differencing

/*
 * This work is licensed under a Creative Commons Attribution 3.0 License.
 * http://creativecommons.org/licenses/by/3.0/
 */
 
/*
 * FrameDifferencing
 * FrameDifferencing class compares two bitmaps and extracts different area
 *
 * @author: Han Sanghun (http://hangunsworld.com/blog)
 * @last modified: 2007-05-24
 * @language version: ActionScript 3.0
 */
 
package{
 
	import	flash.display.*;
	import	flash.events.*;
	import	flash.geom.*;
	import	flash.text.*;
 
	public class FrameDifferencing extends MovieClip{
 
		// image dimension
		private const WID:uint = 89;
		private const HGT:uint = 104;
 
		// source image 1
		private var bd1:BitmapData;
		private var bmp1:Bitmap;
 
		// source image 2
		private var bd2:BitmapData;
		private var bmp2:Bitmap;
 
		// compare image
		private var compare_bd:BitmapData;
		private var compare_bmp:Bitmap;
 
		// different area image
		private var diff_bd:BitmapData;
		private var diff_bmp:Bitmap;
 
		// result movieclip
		private var result_mc:MovieClip;
		private var result_bmp1:Bitmap;
		private var result_bmp2:Bitmap;
 
		/*
		 * FrameDifferencing constructor
		 */
		public function FrameDifferencing(){
 
			// original images
			bd1 = new BitmapData(WID, HGT, true, 0×00000000);
			bd2 = new BitmapData(WID, HGT, true, 0×00000000);
 
			bd1.draw(mc1);
			bd2.draw(mc2);
 
			bmp1 = new Bitmap(bd1);
			bmp2 = new Bitmap(bd2);
 
			// compare 2 images
			var returnObject:Object = bd1.compare(bd2);
			// cast returned Object to BitmapData
			// i don’t know this is right solution, but i have to do this to avoide type mismatch error on compile
			compare_bd = BitmapData(returnObject);
			compare_bmp = new Bitmap(compare_bd);
			addChild(compare_bmp);
			compare_bmp.x = 200;
 
			// hide same area from 2nd image
			diff_bd = bd2.clone();
			var rect:Rectangle = new Rectangle(0, 0, WID, HGT);
			var pnt:Point = new Point(0, 0);
			diff_bd.copyChannel(compare_bd, rect, pnt, BitmapDataChannel.ALPHA, BitmapDataChannel.ALPHA);
			diff_bmp = new Bitmap(diff_bd);
			addChild(diff_bmp);
			diff_bmp.x = 300;
 
			// movieclip to view preview
			result_mc = new MovieClip();
			result_mc.x = 400;
			addChild(result_mc);
 
			// 1st frame image
			result_bmp1 = new Bitmap(bd1);
			result_mc.addChild(result_bmp1);
			// 2nd frame image
			result_bmp2 = new Bitmap(diff_bd);
			result_mc.addChild(result_bmp2);
			result_bmp2.visible = false;
 
			// enterframe event for previewing
			result_mc.addEventListener(Event.ENTER_FRAME, showPreview);
 
		}
 
		/*
		 * showPreview
		 * just show/hide 2nd image to mimic previewing
		 * GIF encoder is not yet completed
		 */
		private function showPreview(evt:Event):void{
			result_bmp2.visible = !result_bmp2.visible;
		}
 
	}
 
}