Failsafe core/non-core context creation on OSX

[mosra]

Currently all Platform::*Application classes create the context with no explicit flags, which is (as far as I know) understood as OpenGL <=2.1 + everything possible on top of it without losing backwards compatibility. While this works on most systems with vendor-provided graphics drivers (Linux, Windows), it apparently fails on (some?) OSX systems.

According to OSX OpenGL capabilities tables there are two kinds of OpenGL support:

• The Legacy one works with older hardware, but provides at most OpenGL 2.1.
• The Core one works only with recent hardware and provides up to OpenGL 4.1, but as it is not backward compatible (only core profile), it must be explicitly requested.

On some systems it was reported that the context in Platform::Sdl2Application can't be created unless explicitly requesting Core profile, e.g. via the following SDL2 calls:

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE)

Sadly this cuts off all Legacy hardware, so we basically don't have any context creation method which would cover all systems.

When I get to it, I will add some context creation options to Platform::*Application::Configuration (i.e., at least version and core/non-core profile specification). But it would be good to have something that just works without explicit configuration (i.e. trying core profile first and if that fails, fall back to legacy).

Anyone with OSX system willing to help with this?

[ArEnSc]

I would be up to solving this issue, assign it to me and ill take a look at the code sometime in the new year, it does not seem to difficult to do.

[mosra]

Thank you! Please send pull request then. Sadly it doesn't seem to be possible to assign an issue without giving full repository access permission yet (see e.g. isaacs/github#100).

[ArEnSc]

The issue with creating a 2.1 compatibility context, that is does hit and miss, even when you explicitly create a new window and a context for it using the SDL_GL_SetAttributes. I think it could be an SDL bug. For creating the 3.2 profile it always works well, so from now on I guess we should document for OSX the core profile opengl 3.2 context is created by default.

[mosra]

Fixed in 5218fda (pull request #43).