Use vendor-neutral OpenGL implementation instead of legacy GLX.

[vanfanel]

Description

Nowadays vendor-neutral GL is used instead of GLX is used in all GNU/Linux distributions.

So, using -lOpenGL works for X11, KMS/DRM and Wayland, while legacy -lGL only works for X11.

Reviewers

@hunterk

[LibretroAdmin]

How would we go about fixing the CI build error for linux-c89?

[vanfanel]

I don't quite understand why this c89 configuration tries to build code with GLX calls.
What configure parameter is causing that?

[gouchi]

@vanfanel For the Linux building of Github CI so we should check for C89_BUILD ?

[MistyDreams]

The c89 fails without this commit anyway.

CC cores/libretro-video-processor/video_processor_v4l2.c
cores/libretro-video-processor/video_processor_v4l2.c: In function ‘libretro_videoprocessor_retro_set_environment’:
cores/libretro-video-processor/video_processor_v4l2.c:286:4: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
  286 |    bool no_content = true;

edit moving that variable up one line will fix the build issue with C89_BUILD=1. Make sure libglvnd packages are installed on the buildbot, if you want to do it this way.

[vanfanel]

@hunterk can you take a look?

[hizzlekizzle]

Hmm, fails with a bunch of glx linking errors on my machine, as well. :/

[gouchi]

Same errors and I have libglvnd.

[vanfanel]

How can it be? It just swaps -lGL with -lOpenGL

Using OpenGL shouldn't imply using GLX code at all. That makes zero sense.

[MistyDreams]

Hmm, fails with a bunch of glx linking errors on my machine, as well. :/

you probably havent installed the libs what distro are you using ill get you the package names this is basic stuff though.

apt install libglvnd0

if thats not installing the libs add a apt-get install libopengl0 and any other libs you might need if they dont auto install with libglvnd0. If its not ubuntu/debian tell me the distro ill get the package names for you.

[LibretroAdmin]

pushed a c89buildfix for the video preprocessor

[vanfanel]

So it should build now?

[keithbowes]

Good idea, but would it be possible to use -lGL if -lOpenGL isn't available? The check_lib function seems not to allow to continue if the library isn't found, but I suppose it would be possible to make a compile-time option like --enable-legacy-glx.

[LibretroAdmin]

Decided to approach this in a different way.

8abe49a

You can build with vendor-neutral GL implementation by running this before compiling:

./configure --disable-glx

[vanfanel]

I love how this ended up being solved :)