[Mesa-dev] [Bug 30172] GL_EXT_framebuffer_blit function required

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Sep 16 21:18:31 PDT 2010


--- Comment #19 from Luca Barbieri <luca.barbieri at gmail.com> 2010-09-16 21:18:31 PDT ---
> ELF weak symbols do not allow one to decide behavior (OpenGL library)
> at runtime -- mangling aside.

AFAIK, glXGetProcAddress also doesn't, because you can call it without a
context bound, and thus libGL has no more information than the one it has at
compilation time.

See http://dri.freedesktop.org/wiki/glXGetProcAddressNeverReturnsNULL

Note, BTW, that wglGetProcAddress returns context-dependent pointers, so it has
some reason for existing (even though it's still an unreasonable burden for the
programmer to have to use it).

> We *still* have to support systems that do not have dlsym  =(

I'm curious, how can such a system exist?
Surely a system with dynamic linking must have something like dlsym (perhaps
with another name, like GetProcAddress in Windows).

And if dynamic linking is not supported, then you'll be limited to a single GL
implementation and thus you don't need dlsym since you know exactly what is
available (and it's better to fail at build time in this case).

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