Begin Fill merge with another fill

Question

Hi all.
Got a problem.
In the below example (if you paste into a new fla with AS3)
you will see that the two squares sit on top of each other. This is
not what I want for a few reasons. I am makeing a brush type tool
that needs to update the shape every time the mouse moves etc.
Is there a way I can make the fill merge with the last fill
rather than sitting on top like a layer. (Surely there must be a
way)
If not can you suggest a way I can do somehting similar. It
is not possible to redraw every fill every time as it would slow
down very quickly.
I goal is to have the user use a square brush. (If a round
brush I would simply use the lineTo to do it quite easily)
var shapeClip:Shape=new Shape();
addChild(shapeClip);
with(shapeClip)
graphics.lineStyle(.25,0x000000,0);
graphics.beginFill(0xFF0000,.5);
graphics.moveTo(10,10);
graphics.lineTo(50,10);
graphics.lineTo(50,50);
graphics.lineTo(10,50);
graphics.lineTo(10,10);
graphics.endFill();
graphics.beginFill(0xFF0000,.5);
graphics.moveTo(30,30);
graphics.lineTo(70,30);
graphics.lineTo(70,70);
graphics.lineTo(30,70);
graphics.lineTo(30,30);
graphics.endFill();
}

Answer 1

Hmm. I've done a lot of investigation and I'm pulling my hair
out with this one.
Surely therre must be a way to merge two shapes
together?