GL Visual Initialization

[Ben Gamari]

Correction: my debugging output was incorrect (serves me right for
trusting debug output over reading the code directly).
filterOutNativeConfigs filters out configs of my default visual, just as
the name would indicate. This makes much more sense as far as naming
consistency, however why it desirable or necessary to filter out native
configs? Wouldn't this make it impossible for the default config to be
expressed as a GLX visual?

- Ben


On Mon, 2008-05-26 at 12:51 -0400, Ben Gamari wrote:
> Hey all,
> 
> For a few months now I've been experiencing an odd bug with GL visual
> initialization (#15641) where the default root visual is not being
> exported as a supported GL visual. This, for obvious reasons, causes
> some issues when running some software (most notably, compiz). While
> school has kept me from putting too much time into debuggin to-date, now
> since classes are over, I have a bit of time to put into finally nailing
> this bug down (and cease the weekly pokes of krh; sorry about that krh).
> 
> I guess my first question is what is the relationship between FBConfigs,
> GLX Visuals, and X Visuals (and "Modes" which are occassionally
> mentioned in the source)? While the respective specs give definitions,
> these really don't offer much help when it comes to how they are all
> generated and interact within the X server.
> 
> Thusfar, I've tried poking around in the X server to identify the code
> path of GL visual initialization and have come up with this,
> 
> - __glXDRIscreenProbe() ->
>   - driCreateNewScreen() ->
>     - intelInitScreen() ->  (I'm on Intel hardware)
>       - intelFillInModes() ->
>         - driCreateConfigs(): (Generate __GLcontextModes, and __DRIconfigs)
>   - glxConvertConfigs() ->  (Generate FBConfigs (aka Modes?) from DRI Configs?)
>     - createModeFromConfig()
>   - __glXScreenInit() ->
>     - filterOutNativeConfigs()
>     - addFullSet() -> 
>       - AddScreenVisuals()  
> 
> Does this look about right? Did I miss any steps? I have been able to
> figure out what some of this code does but without basic background, it
> has been a little tough. From what I can tell, the configs pertaining to
> my default visual (0x21) are being looked at by
> filterOutNativeConfigs(). What precisely is this function supposed to
> do?
> 
> I would be quite grateful if someone with experience with this code
> could spare a few minutes and write down some background and perhaps
> answer some of my previous questions. Thanks a ton,
> 
>  - Ben
> 
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