[cairo] Operator optimization based on source or dest opacity
cairo at antoineazar.com
Fri Feb 29 16:40:18 PST 2008
>- I really don't think it's necessary to have a separate
>pixman_transformed_image_is_opaque(). For destination images, the
> transform and filter are always going to be NULL, so the
> additional check is very quick.
I'll trust you on this one, but where is this specified?
>- The if statement in pixman_transformed_image_is_opaque() is
>difficult to follow for me. It's also broken in at least one case:
> convolution filters can introduce translucency even when there
> weren't any to begin with.
How can a convolution filter introduce translucency in an opaque
image that extends?
> Also, I'm not confident that the pi/2 rotation transformation
> check is correct. Doesn't it need the rotation to be around the center of
> the image?
Any affine transform other than non pi/2-multiple rotations (and
shears) are allowed, as long as we use a nearest filter. Whether the
rotation is around the center of the image or not is irrelevant.
> Can we just add something like this to the end of
> /* Convolution filters can always introduce translucency */
> if (convolution filter)
> return FALSE;
> if (repeat_none && (filter || transformation))
> return FALSE;
> return TRUE;
> then get rid of pixman_transformed_image_is_opaque()?
> I *think* that would be correct, though I would appreciate an
> additional review from someone else.
You'd be missing some optimization cases as I explained above.
Thanks for the careful review Soeren!
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