Support older 2.x series of glbinding as loader for OpenGL3

[DonKult]

For the moment I have only the older 2.x series available on my system
which uses slightly different header filenames and initialisation, so
as a slight variation of the 3.x series support recently implemented
here the glue needed to make 2.x series work.

I would hope a potential 4.x will not change filenames and such, so the
existing flag isn't rebranded to 3 which also avoids breaking compat.

References: #2870, 5e2329b

No worries if you conclude that you don't want to support/include this, I am pushing the PR mostly at the off chance of it helping someone. That might already be achieved with the references. 😁

[ocornut]

Hello and thanks for this PR.

I would hope a potential 4.x will not change filenames and such, so the
existing flag isn't rebranded to 3 which also avoids breaking compat.

I totally see the point and logic here and would have probably initially done the same, but the end result seems to be really misleading for the end-user since the expectation is that 2 comes after the unnumbered one.

My suggestion would be to backtrack on that specific aspect:

• Rebrand the existing define as IMGUI_IMPL_OPENGL_LOADER_GLBINDING3.
• Add extra comments in Makefile, top of main.cpp files (where the files are included) to more clarily state that the other is 3.x+
• If it happens to work with 4.x it'll be more natural to add a comment saying it also works for 4.x+, or even additional constructs to redirect one version define to the other.

Also note that both main.cpp and Makefile in example_sdl_opengl3/ would be the be updated identically to the example_glfw_opengl3/ files, you may copy and paste those changes even if you can't compile with SDL.

Thank you!

[DonKult]

Yeah, you are right that versioned and unversioned is confusing. I am just kinda suspecting I am more or less the only one left with version 2 usage (as version 3 is 20 months old by now) so I want to avoid disturbing others too much…

So, how about using the unversioned define for auto-detection and two explicit versioned ones for all those with specific needs or compilers not supporting c++17 yet. The new version of the commit tries to implement this. (Also for SDL… completely overlooked that.)

[ocornut]

Thanks for the update!
I noted a typo above (breaking the SDL example).

Looking at this, I feel that removing support for the unnumbered define would clear things out. I was surprised you added it. Note that IMGUI_IMPL_OPENGL_LOADER_GLBINDING was introduced this January, you may be its second or third user, so I feel it is saner to just remove all occurrences. Whoever are the few people using it will quickly realize the define has been renamed (and we'll post to the other thread to let them know).

This way we can clear out the Makefile and the impl_.h file from excess cruft. We can keep the lower ___has_include auto-detection block, the remaining auto-detection block becomes more trivially noise-free.

Using IMGUI_IMPL_OPENGL_LOADER_GLBINDING2 IMGUI_IMPL_OPENGL_LOADER_GLBINDING3 without the underscore would be a little more consistent with our other code.

Finally you may add a note at the top of imgui_impl_opengl3.cpp and in docs/Changelog.txt but if you are not sure about it I'll just them add over your commit when merging.

Thanks for your help and patience!

[DonKult]

My middle name might as well be "No breaking change" so little ifdef trickery and feature detection comes natural to me. No worries, if that isn't house-style I can adapt (after all, breaking house style is a form of breaking change…). Pushed v3 hopefully with all the suggested changes & maybe less copy&paste mistakes. Thanks for your help and patience as well!

I haven't add changelog entries here or there though. Please do as needed.

[ocornut]

Merged now, thank you!