> > I'm inclined to believe that the comments in dri_glx.c are just > > wrong. __glXRegisterExtensions has to be called before a call to > > glXGetProcAddress. The app can query that string via > > glXQueryExtensionsString long before calling glXGetProcAddress. In > > fact, it may never call glXGetProcAddress. I'm sure glxinfo > > doesn't. :)
On the other hand, the app can call glXGetProcAddress without opening a display or creating a context. If you follow the letter of the spec the only way to be sure that a extension is supported is by inspecting the extensions string, and for that you need a display.
> So this does influence which extensions are listed in the extension > string, contradicting what Keith wrote? In that case I have one more > question. How can this work with multi-head configurations where you > can have multiple different cards (different screens) on one display. > Then each driver will add or readd extensions. But they should never > disable any extensions, right? You don't want drivers to disable each > others extensions, do you?
Intuitively glGetString(GL_EXTENSIONS) should return the list of the extensions supported on the context that's current.
For GLX extensions glXQueryExtensionsString is used. All this function gets is a Display pointer and a screen number.
That doesn't say anything about the extension being supported in hardware or software, which is I think the point of your question. That means that if the driver supports the extension and the extension is not precluded by the current context the extension should be reported as being supported. I remember someone on this list mentioning that the NVIDIA drivers do something fuzzy in this respect.
OTOH, if you are talking about GLX extensions, most don't make sense without hardware support.
Right. As an example, we don't want the R200 driver to expose GLX_MESA_swap_control if there's no vblank interrupt available. Since it can't implement the functionality, we don't want to advertise it.
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