package {
	import flash.display.BitmapData;
	public class Subtractor {
		public var threshold:uint; // 影化のしきい値
		public var bg:BitmapData;
		public var bmd:BitmapData;
		public var shadow:Shadow;

		public function Subtractor() {
			threshold = 30;
			shadow = new Shadow();
			bg = new BitmapData(shadow.width, shadow.height);
			bmd = new BitmapData(shadow.width, shadow.height);
			trace("construct: Subtractor");
		}
				
		public function subtract():void {
			for (var y:int = 0; y < bg.height; y++) {
				for (var x:int = 0; x < bg.width; x++) {
					if ( comparePixels( bg.getPixel(x, y), bmd.getPixel(x, y), threshold ) ) {
						shadow.setPixel(x, y, true);
					} else {
						shadow.setPixel(x, y, false);
					}
				}
			}
			shadow.updateBitmapData();
		}
		
		function comparePixels(a:uint, b:uint, threshold:uint):Boolean {
			var a_red:int = a>>16&0xFF;
			var b_red:int = b>>16&0xFF;
			var a_green:int = a>>8&0xFF;
			var b_green:int = b>>8&0xFF;
			var a_blue:int = a&0xFF;
			var b_blue:int = b&0xFF;
			if ((a_red > b_red && a_red-b_red > threshold) || (a_red < b_red && b_red-a_red > threshold) ||
			   (a_green > b_green && a_green-b_green > threshold) || (a_green < b_green && b_green-a_green > threshold) ||
			   (a_blue > b_blue && a_blue-b_blue > threshold) || (a_blue < b_blue && b_blue-a_blue > threshold)
			   ) {
				return true;// 色に差がある時
			} else {
				return false;
			}// 色に差が無い時
		}
	}

}