[cairo] unbounded by source operators != unbounded by mask operators

[Carl Worth]

On Thu, 27 Oct 2005 19:10:57 -0700, Keith Packard wrote:
> I've found several places in the code which want to know whether the
> operation is bounded by the source and are using _cairo_operator_bounded
> in conjunction with explicit tests for SOURCE and (sometimes) CLEAR
> operations. This seems silly to me, and I also wonder if some of these
> existing cases are wrong as they don't check for CLEAR.
> 
> I suggest renaming our existing function and adding a new one:

Good catch Keith, and I like the distinction in the functions and
their names here.

Two minor notes/questions on the documentation of the new function:

>  * A bounded operator is one where source pixels (not just alpha)
>  * of zero results in no effect on the destination image.

What does the "(not just alpha)" refer to here? That's not clear to
me.

>  * Unbounded operators often require special handling; if you, for
>  * example, copy a surface with an unbounded operator, the effect
>  * extends past the bounding box of the surface

"copy a surface with an unbounded operator" ? Wouldn't it be more
clear to just say "if you, for example, draw with the SOURCE operator,
the effect extends" ?

-Carl
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