[cairo] Bug with paint_with_alpha and perf issues when compositing with SOURCE

[Carl Worth]

On Tue, 27 May 2008 09:11:17 -0400, Owen Taylor wrote:
> On Thu, 2008-05-01 at 03:34 -0400, Antoine Azar wrote:
> > Hey all,
> > I discussed this already with cworth and am looking for feedback on
> > this issue.
> >
> > paint_with_alpha will return an "incorrect" result when used with a
> > SOURCE operator. According to the doc, paint_with_alpha is "A drawing
> > operator that paints the current source everywhere within the current
> > clip region using a mask of constant alpha value alpha. The effect is
> > similar to cairo_paint(), but the drawing is faded out using the alpha
> > value."
...
> Which doc is this?

Antoine is quoting our current documentation for
cairo_paint_with_alpha as seen here:

http://cairographics.org/manual/cairo-cairo-t.html#cairo-paint-with-alpha

> I can sort of see why you think that paint_with_alpha() should be
> different ... there's an intuitive understanding of the operation as
> "make the source partially transparent and then paint it"... but that's
> not how it's defined.

Right. That intuitive understanding is what's described in the
documentation there and seems to be what was tripping up
Antoine. Maybe the phrasing of "the effect is similar to" just needs
to be "the effect (with the default OVER operator) is similar to" in
order to be accurate?

-Carl
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