[cairo] Simplifying the operator set

[Carl Worth]

On Fri, 7 Jan 2005 10:13:25 -0800, Bill Spitzak wrote:
> On Thursday 06 January 2005 10:45 pm, Carl Worth wrote:
> >                 "A atop B is the union of A in B and B out A"
> >                 "A xor B is the union of A out B and B out A".
> 
> Actually they are the *sum* of the component operations.
> 
> The word "union" implies to me the "A+B-AB" operation, ie what happens to the 
> alpha in "over" and in many of the photoshop style operators.

Well, "union" was Porter/Duff word choice, not mine. ;-)

But, we do have an ADD operator, so these operators should be
straightforward (if awkward) to emulate. That sounds fine to me since
I don't know of any common use case for ATOP or XOR that justifies
keeping them easy.

So, if nobody objects, I'll drop them.

-Carl