gl: Relax GLSL requirement from 3.3 to 3.1

[plaes]

With these changes, it is possible to start dethrace on
Pinebook Pro (Mali-T860 / Panfrost):

OpenGL vendor string: Panfrost
OpenGL renderer string: Mali-T860 (Panfrost)
OpenGL core profile version string: 3.1 Mesa 22.3.0-devel (git-d08bd9a8d8)
OpenGL core profile shading language version string: 1.40

[dethrace-labs]

thanks! Your core profile reported in your output is 3.1, just curious if you tried to set SDL_GL_CONTEXT_MINOR_VERSION to 1 without any other changes? Does that also compile and run?

Just curious, trying to understand the various OpenGL version conventions!

[plaes]

thanks! Your core profile reported in your output is 3.1, just curious if you tried to set SDL_GL_CONTEXT_MINOR_VERSION to 1 without any other changes? Does that also compile and run?

Just curious, trying to understand the various OpenGL version conventions!

After changing the version to 3.1, it built, but failed to compile shaders runtime:

[PANIC] CreateShaderFromFile shader vertex_shader_2d.glsl failed to compile: 0:1(10): error: GLSL 3.30 is not supported. Supported versions are: 1.10, 1.20, 1.30, 1.40, 1.00 ES, and 3.00 ES

And after fixing the shaders (I eventually settled to lowest possible requirements), it crashed because due to glFrameBufferTexture requires at least OpenGL 3.2. (So calling it resulted in null pointer exception).

[dethrace-labs]

I have to keep the core profile active since I'm on a Mac and without the core profile it falls back to OpenGL 2.1.

I suggested some changes to the PR that still work on my machine and should work on yours too, in theory!

The change from glFrameBufferTexture to glFrameBufferTexture2D is fine, I actually made the same change myself in a different branch

[dethrace-labs]

@plaes when you have a minute, could you help validate the suggested changes? thanks!

[plaes]

@plaes when you have a minute, could you help validate the suggested changes? thanks!

Pushed the changes and validated they work too.

[dethrace-labs]

thanks very much!

[dethrace-labs]

@plaes could you take a quick photo of it running on your pinebook? I'd love to throw it up on our twitter feed :)