Класс вращения объекта вокруг произвольной точки

Код AS3:

package com.in4core.transformation 
{
	import fl.motion.MatrixTransformer;
	import flash.display.DisplayObject;
	import flash.geom.Matrix;
	import flash.geom.Point;
	/**
	 * $(c)2011
	 * 
	 * @author in4core
	 * 
	 * About :
	 * 
	 * RotationPoint is a static class for rotation DisplayObject around freePoint.
	 * For define internal Point use RotationPoint.internalPoint property.
	 * For define internal Matrix use RotationPoint.internalMatrix property.
	 * For begin rotation use RotationPoint.rotateAroundPoint method.
	 * 
	 * ...
	 * version 1.0
	 */
	public class RotationPoint 
	{
		private static var _defaultPoint:Point = new Point(0, 0);
 
		private static var _defaultMatrix:Matrix = new Matrix();
 
		private static var _localMatrix:Matrix = new Matrix();
 
		public static function set internalPoint ( p : Point  ):void {
 
			_defaultPoint = p;
		}
 
		public static function set internalMatrix ( m : Matrix ) : void {
 
			_defaultMatrix = m;
		}
 
		public static function rotateAroundPoint ( disObj : DisplayObject , angle : Number ):void {
 
			disObj.transform.matrix = _defaultMatrix;
 
			_localMatrix = disObj.transform.matrix;
 
			MatrixTransformer.rotateAroundInternalPoint ( _localMatrix  , _defaultPoint.x, _defaultPoint.y , angle );
 
			disObj.transform.matrix = _localMatrix;
 
		}
 
		private static const VERSION = 1.0;
	}
 
}

Код AS3:

RotationPoint.internalPoint = new Point(obj.width/2 , obj.height/2) // если точка в центре
RotationPoint.internalMatrix = obj.transform.matrix;
RotationPoint.rotateAroundPoint ( obj , 20 );