var lineSize:Number=40;

var drawnBitmapData:BitmapData = new BitmapData(210, 145, true, 0x00000000);

var drawnBitmap:Bitmap = new Bitmap(drawnBitmapData);

var erasableBitmapData:BitmapData = new BitmapData(210, 145, true, 0xFFFFFFFF);

var erasableBitmap:Bitmap = new Bitmap(erasableBitmapData);

erasableBitmap.cacheAsBitmap = true;

addChild(erasableBitmap);

maskee.cacheAsBitmap = true;

maskee.mask = erasableBitmap;

var eraserClip:Sprite = new Sprite();

initEraser();

function initEraser():void {

        eraserClip.graphics.lineStyle(lineSize,0xff0000);

        eraserClip.graphics.moveTo(stage.mouseX,stage.mouseY);

        stage.addEventListener(MouseEvent.MOUSE_MOVE,maskMove);

}

 

function maskMove(e:MouseEvent):void {

                // Draw a line to current mouse position

                eraserClip.graphics.lineTo(stage.mouseX,stage.mouseY);

                // Clear the drawn bitmap by filling it with a transparent color

                drawnBitmapData.fillRect(drawnBitmapData.rect, 0x00000000); 

                // Copy our eraser drawing into the erasable bitmap

                // (This is required to ensure the smooth alpha edges on our eraser are retained)

                drawnBitmapData.draw(eraserClip , new Matrix(), null, BlendMode.NORMAL);

                // Fill the erasable bitmap with a solid color

                erasableBitmapData.fillRect(erasableBitmapData.rect, 0xFFFFFFFF);

                // Copy the scribble bitmap to our main bitmap, with blendmode set to ERASE

                // This erases the portion of the mask that has been drawn.

                erasableBitmapData.draw(drawnBitmap, new Matrix(), null, BlendMode.ERASE);

}

 

function startDrawing(e:MouseEvent):void {

        eraserClip.graphics.moveTo(stage.mouseX,stage.mouseY);

}