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If I ask for OpenGL version 2.1 via



what can be guaranteed (assuming no failure on SDL_CreateWindow (with SDL_WINDOW_OPENGL)?

The documentation says SDL_GL_SetAttribute doesn't necessarily guarantee anything... but I'd think with version it might fail if you don't get the one requested? Or is it like "you get version at LEAST what you request"?

Also, does anyone know of a straightforward resource (or just tell me) for what openGL versions are available with various platforms?

For example, OSX? I assumed it would be safe to ask for 2.1, but I do and I seem to be getting 4.1... (via glGetIntegerv(GL_MAJOR_VERSION, ...))

Ok, so apparently with SDL_GL_CONTEXT_PROFILE_CORE you can only get OpenGL 4.1 on OSX? And SDL_GL_CONTEXT_PROFILE_COMPATIBILITY you should get 2.1 (which is what I want!).

However, now when getting the version with glGetIntegerv(GL_MAJOR_VERSION, ...), which I had used before to correctly deduce that I was being given an OpenGL 4 profile, I am getting 32767 (the max int size for a signed 32 bit int). That response doesn't seem to be documented anywhere in either the SDL or the OpenGL docs, so I'm at a loss.

What's weirder still is that glGetString(GL_VERSION) IS returning "2.1 INTEL-10.6.31". Which is weird.

Any ideas?

I have had similar questions to you which have also been bugging me. I also would like to know exactly what OpenGL context I have once I have set the flags.

I tried playing around on both my PCs at home, and I added some legacy OpenGL code to my project to test the context. Using the following code I set my OpenGL context :

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, ...);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, ...);

However on both PCs if I set it to 3.2 or higher the legacy code won't render (which I expected as I presume I am now in a modern forward compatible OpenGL context). If I set it to 3.1 or lower, the legacy code will render. Okay, so far so good. The issue though is two things.

1. If I set the context to 3.1 or lower and call glGetString(GL_VERSION) the output is always 4.5 on one PC and 4.4 on the other (One PC is better than the other). The fact remains that my legacy code runs, so I know I am in the 3.1 or below context. But it tells me I'm in a 4.4 / 4.5 context. If I set it to 3.2 or higher and call glGetString(GL_VERSION) I get exactly the context I asked for, eg 3.3 or 4.2 etc. But the question is why? Does the graphics card not recognise anything less than 3.2?

2. The other burning question is if I leave out SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, ...) and SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, ...) and query OpenGL what context I am in, it tells me 4.5 or 4.4 (depending on PC used) BUT my legacy code renders, so what I presume here is that I am in an older OpenGL context BUT again the graphics card doesn't recognise older versions when calling glGetString(GL_VERSION) so it just says the latest one instead.

If anyone knows any better, please share their thoughts, as this is a little confusing to say the least.