Problem with actionscript 3 erasing drawing

I have a based image and some sprites on top of the basd image movieclip... Some of the sprites can be drawn by the user using graphics api in actionscript 3. I can draw things on the sprites but I can't create an eraser like brush that can remove part of the unwanted drawings. I try using Alpha but no it doesn't work

I have googled about it and come up with the solution:

1) Linebitmapstyle... This solution is not the best one coz I my sprites can be moved so if I us开发者_JS百科e linebitmapstyle, it does draw the pixel from the image to the sprite but if the sprite moved the drawn pixel won't change.

2) Masking may not work for me either....

What is the best way of creating the eraser

You may rather want to use a Bitmap to make such things easier to manipulate (unless you need to do scalable vector graphics of course!). To draw shapes you can still use the graphics API to create the shapes.

To do so, instantiate a "dummy" sprite (or another IBitmapDrawable implementation) to create the graphics and then "copy" them to the BitmapData the bitmapData.draw() function. This way you can for instance draw with the option BlendMode.ERASE in order remove the pixels of the shape.

Example (from the top of my mind) :

// creates a bitmap data canvas
var bitmapData:BitmapData = new BitmapData(500, 500);

// creates a bitmap display object to contain the BitmapData
addChild(new Bitmap(bitmapData));

// creates a dummy object to draw and draws a 10px circle 
var brush:Sprite = new Sprite(); // note this is not even added to the stage
brush.graphics.beginFill(0xff0000);
brush.graphics.drawCircle(10, 10, 10); 

// the matrix will be used to position the "brush strokes" on the canvas
var matrix:Matrix = new Matrix();

// draws a circle in the middle of the canvas
matrix.translate(250, 250);
bitmapData.draw(brush, matrix

// translates the position 5 pixels to the right to slightly erase the previously
// drawn circle creating a half moon            
matrix.translate(5, 0);
bitmapData.draw(brush, matrix,null,BlendMode.ERASE);