On May 6, 2007, at 16:12 , Jim Rosenberg wrote:

> Consider two rectangles, a and b. The only constraint I will put on  
> them is that neither contains the other. I wish to create a  
> PolygonMorph programmatically consisting of a merge: b with b  
> removed but all of a retained in the case a and b overlap. I think  
> I see my way to how to do this, but if anyone knows of any code I  
> can look at where something like this is already implemented I'd be  
> much obliged.
>
> My idea for how to go about this is to use "turtle logic" more or  
> less as follows: Start with the first vertex of a merge: b which is  
> not inside of b. Proceed clockwise along the bounds of a merge: b;  
> if you hit b turn left, if you hit a turn right. But this may be  
> doing things the hard way.

Sounds reasonable. There is a polygon clipper in Rome that you could  
take a look at. The class is named RomePolygonClipper in package Rome- 
Reference at

	http://squeaksource.com/Rome.html

Might be simpler if you state the larger problem you need this for.

- Bert -