[cairo] Redoing SOURCE and CLEAR

[Carl Worth]

On Wed, 17 Aug 2005 16:28:14 -0400, Owen Taylor wrote:
> I'll skip adding commentary here and let the images stand on their
> own.

Well, I'll comment on it then.

Fantastic work, Owen!

These pictures are exactly what I needed to convince myself we want
the new equation. Under the new equation, the operator controls the
interaction of source and dest, while the shape and clip are only used
to restrict the behavior. As the images show, this provides consistent
behavior across all operators, and unique results for each.

And if the old behavior is ever useful, it looks like it would be
simple enough to obtain with an extra CLEAR and some intermediate
surface juggling, (even less juggling if we add the INVERSE_FILL rules
at some point).

How's the patch looking for this now? Is there a lot of churn needed
to get the same level of optimization with the new equation?

Or do we get to throw away a lot of the "unbounded clearing" code?

So, I guess what we've done is to reduce "fill" to be conceptually
equivalent to "clip; paint"? (with the exception of SATURATE). That's
not unpleasant.

-Carl
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