var flag:Boolean = false;

 

var mymask:Sprite = new Sprite();

addChild(mymask);

 

mypic.mask = mymask;

 

stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDowns);

stage.addEventListener(MouseEvent.MOUSE_MOVE, onMouseMoves);

stage.addEventListener(MouseEvent.MOUSE_UP, onMouseUps);

 

function onMouseDowns(event:MouseEvent):void

{

        flag = true;

}

 

function onMouseUps(event:MouseEvent):void

{

        flag = false;

}

 

function onMouseMoves(event:MouseEvent):void

{

        if (flag)

        {

                mymask.graphics.beginFill(0x000000);

                mymask.graphics.drawCircle(mouseX, mouseY, 40);

                mymask.graphics.endFill();

        }

}