private function init():void {
                          eventSprite = new Sprite();
                          addChild(eventSprite);
                          eventSprite.graphics.beginFill(0xff0000);
                          eventSprite.graphics.drawCircle(0, 0, 100);
                          eventSprite.x = stage.stageWidth / 2;
                          eventSprite.y = stage.stageHeight / 2;
                          eventSprite.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);          
                          eventSprite.addEventListener(MouseEvent.MOUSE_UP, onMouseUp);
                  }