Revert "opengl32: Return a NULL pointer for functions requiring unsupported or disabled extensions.".

[Sebastian Lackner]

On 27.11.2015 06:21, Alexandre Julliard wrote:
> Henri Verbeet <hverbeet at gmail.com> writes:
> 
>> Essentially, I think the number of affected users doesn't outweigh
>> doing the correct thing in this case.
> 
> Correct me if I'm wrong, but isn't this simply a matter of returning
> glCopyTexSubImage3D if glCopyTexSubImage3DEXT is missing?  That seems a
> better solution than relying on quirks of the Nvidia driver.
> 
> Could someone please give this a try so that we can solve this
> regression for 1.8?
> 

@Henri: Thanks for the explanation about the difference of wglGetProcAddress
and glXGetProcAddress, I wasn't aware that the Windows version works more
reliable, which explains why you would like to keep this part. Do you see
any other chance to implement a more general detection which functions are
available, than to rely on the extension string? Analyzing thunk wrappers,
or doing a test call with exception handler would probably work, but sounds
a bit too ugly. :/

@Alexandre: Just to make sure I tested it in practice, and it indeed solves
the bug. It would be acceptable but 1.8, but wouldn't solve
https://bugs.winehq.org/show_bug.cgi?id=39563 for example. I am aware that
its technically not a Wine bug, but it could still be solved by being less
strict with extension filtering. Both MESA and NVIDIA return valid valid
function pointers in this case.

Regards,
Sebastian