Optional glbinding as OpenGL binding

[scheibel]

This week my team published an alternative OpenGL binding beside GLEW.
As a simple test we tried to replace the OpenGL binding of known open-source software with ours: glbinding.

For SuperTux this was a pleasingly simple task.
I just want you to be able to use our work we have done while integrating glbinding.
If you pull this PR into your branch, the build defaults to the exact same setting as without this PR.

That has been done:

• add glbinding as optional dependency
• add an option that glbinding can be used instead of GLEW
• add another option to enable per OpenGL-function tracing during runtime
• adapt OpenGL-dependent code so that it works with both GLEW and glbinding

I know this is just a mirror, but if you're interested in the code you can merge this PR in your internally used git-Repository.

[tobbi]

I am no expert in CMake, but shouldn't this option be called USE_GLBINDING since we're referencing USE_GLBINDING later in the code (l. 84)?

[scheibel]

Originally, I named this option like this, but I changed it to GLBINDING_ENABLED when I added the second glbinding option, so that they get grouped by the cmake gui.
I'm not attached to the exact naming of the options, they can be renamed to whatever you like.

[tobbi]

Alright, but they should be the same in line 75 and line 84, so that this actually works, right? In any case: Many thanks for your work.

[scheibel]

Yes, they have to have the same name, I fixed this.

[tobbi]

I can merge this, but I keep getting a crash when I try to start SuperTux with glbinding:
http://pastebin.com/Gf8TeqrT

[scheibel]

I see that you have used OS X as operating system.
I tested my code on Ubuntu 14.04 where all works just fine.
It seems like a bug in glbinding on OS X where function addresses aren't resolved correctly but I'm pretty sure that we fixed this bug a long time ago.
I might be able to test it on OS X on monday and try to fix this issue.

Thanks for the extensive crash report.

[scheibel]

I moved the glbinding initialization code behind the context creation code, where it belongs.
One of our team members has reproduced the error on his OS X machine and is about to test this fix.

[tobbi]

I squashed all commits and applied the pull request on our repository with git revision f266dcd. Changes should appear on this mirror within the hour. In case there are any problems arising, I will get back to you.

Thanks for your contribution! :-)

[tobbi]

Hmm, sorry, this was quick, but I accidentally wasn't compiling with glbinding. It still crashes at startup on my Mac 10.9. Please see pastebin for the error message:
http://pastebin.com/a4wb40vS

[scheibel]

It seems that on OS X an OpenGL context below version 3.0 is used (I assume 2.1), so querying extensions fails.
Therefor we integrated a special test for OpenGL version < 3.0 and return an empty list instead of querying the OpenGL driver.

This is implemented in the no_extensions_below_3_0 branch of glbinding.
Does the current SuperTux code work with the specific branch of glbinding?
If so, we will merge the branch into the master so this piece of code is integrated into the 1.1 release.

[tobbi]

The abovementioned branch works, albeit being rather slow. I can upload the log which contains the opengl calls from starting supertux to loading the first worldmap, however, it's 95 MB big, which is too big for any pastebin service.

[scheibel]

Of course, with ongoing write to disk, the program is much times slower.
You used the debugging mode, which we used to analyse the OpenGL calls made by SuperTux.
There is the CMake option GLBINDING_DEBUG_OUTPUT that can be turned off in order to reduce the functionality of glbinding to a bare OpenGl function binding.
This should be as fast as using GLEW.

[tobbi]

You're right. Disabling that debug statement fixed it. Done the final change in commit 8415881 and closing this. Many thanks, again!