Blur filter + mask

Question

I think a couple people asked about this problem but none of them seemed to get an answer so I am re-posting.
This is how blur filter and mask work in code
var blur:BlurFilter = new BlurFilter();
blur.blurX = 10;
blur.blurY = 10;
var mask:Bitmap = new Bitmap(...)
var shape:Shape = new Shape();
shape.graphics.beginFill(color, alpha);
shape.graphics.moveTo(100, 100);
shape.graphics.lineTo(...);
shape.graphics.endFill();
shape.filters = [blur]
shape.mask = mask;
bitmap.bitmapData.draw(shape);
But result is not what I want. Please see the below image:
Making another bitmap and copy pixels using the mask works but it makes whole applcation very slow.
How can I mask blur filter using a single draw?

Answer 1

The difference between the code I posted and what you have there is that you are applying the mask and the blur to the shape, whereas I applied the blur to the shape and the mask to a container the shape is inside. This is because for a given object the filters apply AFTER any masking, but you want the reverse. The only way to control the order that I know if is to create more layers.
In other words, change the last code you posted like this:
1. Create a container for the shape:
var container:Sprite = new Sprite();
2. Add the shape to the container:
container.addChild(shape);
3. Apply the blur to the shape, and the mask to the container:
shape.filters = [blur];
container.mask = block;
3. Draw the container to the bitmap:
bitmap.bitmapData.draw(container);
That should produce the image you want.
-Aaron