How to switch from ARGB to BGRA colors?

Clemens Koller clemens.koller at
Tue Aug 21 15:07:40 PDT 2007

Hi, Alex, Simone!

>> Now switched to using the Xorg 501 driver.  We have seen issue with yellow
>> shadowing around fonts.

Seems to be the same issue over here with the sm501.
(remember: ARGB <-> BGRA)
It looks to me like the alpha channel is a missing blue
(resulting in a yellowish shadow) and not transparency.

>>  This looks similar to an issue we 'corrected' when
>> using acceleration.  This was caused by the use of an int for colour in the
>> acceleration functions.  We end up 0x7FFFFFxx for white instead of
>> 0xFFFFFFxx.  I'll let you know if we get anywhere with the fonts.
> I'll happily commit patches to the xorg 501 driver if you fix this or
> add any other featured you feel would be useful to others.

I would be also glad to help and debug that stuff on PowerPC
if you provide me some patches / pointers / hints / ideas...

Is there some documentation available how a pixel gets handed through
the functions from a Xorg window out to the framebuffer or hardware?

The PowerPC instruction set has some nice instructions like stwbrx
(Store Word Byte Reverse Indexed) and friends which could
save a lot of hassle reordering the color values here.

Clemens Koller
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Str. 45/1
81379 Muenchen
Phone: +49-89-741518-50
Fax: +49-89-741518-19

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