Compositing issues with 30-bit RGB visuals

[Kai-Uwe Behrmann]

I am not sure where to start and seek for input on a problem with KWin and 
Compiz. They show very similiar wrong rendering of borders, shadows and 
the logout screens.

In compiz is a RGBA buffer used to contruct window borders and shadows:
/* all pixmaps are ARGB32 */
     format = XRenderFindStandardFormat (xdisplay, PictStandardARGB32);

A sreenshot suggests that the 8-bit buffers are blended as is into the 
30-bit visuals. What is the correct way to blend in the final frame buffer 
image with XRenderComposite()?

As a side note, the window contents are almost fine with the exception of 
FF and GTK2 drawing areas.

kind regards
Kai-Uwe Behrmann
-- 
developing for colour management 
www.behrmann.name + www.oyranos.org