[cairo] Alpha masks

[Nathan Hurst]

On Fri, 7 Jan 2005, Carl Worth wrote:

> And I guess the other thing that I don't like about this is that we
> end up with infinitely large geometry. For some reason, it's easy for
> me to accept operators with infinite effects, (eg. draw a small object
> with SRC and the output is cleared to infinity outside the
> object). But it feels much more awkward to have to deal with
> infinitely large operands.

If you only require 'regions' to have a finite boundary and allow the
winding number/alpha outside the region to be non-zero then 'regions' are
still closed under all the operations.  So they aren't really infinite
operands, merely operands that can be inside out.  (You can even introduce
half-planes without complicating things much :)

njh