[cairo] [RFC] Pixman & compositing with overlapping source and destination pixel data

Bill Spitzak spitzak at thefoundry.co.uk
Thu Jun 4 03:11:28 PDT 2009

Cairo can do a transformation when copying (like a rotation or scale). I 
think it is best to say that no guarantee is made when the source and 
destination intersect. You could say it works if there is no 
transformation other than integer translation but it seems a little 
artificial to me. It seems most consistent to say that nothing is allowed.

Also on modern graphics systems it is probably a lot easier to write and 
just as fast to just draw the entire image over again in it's new 
position, rather than trying to copy areas. Or if copying an area really 
does help, making the entire image in an off-screen surface and copying 
from that would work better.

Soeren Sandmann wrote:
> Siarhei Siamashka <siarhei.siamashka at gmail.com> writes:
>> What kind of guarantees (or the lack of) pixman and XRender are supposed to
>> provide when dealing with overlapping parts of images?

Bill Spitzak, Senior Software Engineer
The Foundry, 1 Wardour Street, London, W1D 6PA, UK
Tel: +44 (0)20 7434 0449 * Fax: +44 (0)20 7434 1550 * Web: 
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