[quake2] difference between glx and sdl opengl implementation

Anders Storsveen wakko at generation.no
Wed Mar 23 18:36:41 EST 2005

ok, guys I was playing around with nvidia-settings and I found the root of  
the problem.

GLX somehow gets access to hardware gamma, while sdl does not (and uses  
some software hack to make it happen). This results in much poorer  
quality, while hwgamma justs ups the gamma and keeps the contrasts and  
stuff the software gamma (which i call it, I have no idea what it is)  
justs makes colors brighter.

I tested this while using nvidia-settings and using the gamma-slider the  
following way.
When using glx and sdl in fullscreen, both at the lowest gamma setting  
under the video menu they look quite similiar, however when setting both  
to max they look very different, glx far superior. but when going to  
windowed mode, they both look just the same again. This seems to me that  
when going to fullscreen, the desktop gives up its hold over hwgamma and  
glx picks it up and uses it, while sdl does not. This could be that sdl  
just doesn't do it at all, or that they use different fullscreen modes or  
something, that in sdl's case doesn't free up hwgamma.

Another proof that hwgamma is used on glx and not on sdl is that if you  
actually set hwgamma with the nvidia-settings gamma-slider to about 1.9  
which i would believe is around the max of the gamma slider in q2, the  
colours, contrast and texture looks just like glx does.

I tried to peek a little into the code, but I'm not experienced enough to  
make anything useful out of it, i'm also not sure what files to look in.  
This could be a very simple problem to fix, so it would be great if  
someone could look into it because hwgamma is FAR better than software  
gamma. Also, I personally can't use glx because of the buggy mouse  
(acceleration and negative movment when moving slow).

On Sun, 20 Mar 2005 04:12:29 +0100, Anders Storsveen <wakko at generation.no>  

>  from where does sdl/glx get this information, how do you set it, and  
> what is it set to?
> On Fri, 18 Mar 2005 19:45:43 +0100, Julien Langer <jlanger at zigweb.de>  
> wrote:
>> On Fr, 2005-03-18 at 19:31 +0100, Anders Storsveen wrote:
>>> well, strangest thing just happened!
>>> I was testing around with this to check if it affected the mouse.
>>>      SubSection  "extmod"
>>>          Option  "omit xfree86-dga"
>>>      EndSubSection
>>> what I found is that, when having it like this:
>>>      SubSection  "extmod"
>>> #        Option  "omit xfree86-dga"
>>>      EndSubSection
>>> the colors of glx opengl was dark and un-pretty, but when I removed the
>>> comment again and restarted X the colors where back to "normal" the  
>>> yellow
>>> bright hue I like! Apparently xfree86-dga somehow affects the
>>> color-rendering... Anyone have any idea why?
>> Hmm...maybe you have changed some colour settings in your xserver?
>> With DGA enabled (DGA stands for Directs Graphic Access) the game also
>> accesses your graphic hardware directly, bypassing the xserver I think.

Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

More information about the quake2 mailing list