Compositing issues with 30-bit RGB visuals

Pierre-Loup A. Griffais pgriffais at
Tue Oct 18 20:10:28 PDT 2011

On 10/17/2011 11:41 PM, Kai-Uwe Behrmann wrote:
> 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()?

Is the problem that the destination picture is created with the wrong 
format? To create a Picture around the root window, the WM probably 
wants to use PICT_a2r10g10b10 when it's depth 30 instead.

Are you trying to fix the same bug that I reported a while back?

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

I believe Damien Leone (CCed) came up with a patch for GTK that should 
fix the issue you're seeing? He attached it to a bug you filed back in July:

Have you tried applying that to see if it fixes the non-WM related 
issues you're seeing?

  - Pierre-Loup

> kind regards
> Kai-Uwe Behrmann

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