Refactor rendering to use SDL3 GPU

[NoelFB]

This is more of just a long term intention of replacing the current custom rendering API implementations with SDL3's GPU api, once it is ready.

This will likely require breaking changes to the C# Shader API as I believe the plan is for SDL3 to have a custom shader language.

[NoelFB]

I'm likely going to try implementing https://github.com/thatcosmonaut/SDL/tree/gpu in a branch. It's a SDL3 GPU implantation proposal that I think has a good chance of going through, and I've been following its development for quite a while. I think I'll likely keep OpenGL support as well to keep potential webgl and older platforms functional, but long term if it works out I might move to it entirely.

At which point, the entire current C layer's usefulness is really up for debate. There's still a fair amount of stuff (image loading, font loading) that really requires a native library but SDL3 (with this GPU implementation) really covers everything else required...

[MrBrixican]

Sounds great. I've been following development as well and I'm interested to see how complex using the new API is in practice compared to using particularly verbose backends directly (looking at you Vulkan). From what I can see it's not horrible, but still certainly a big shift in thinking from OpenGL. Also curious as to if there's any performance gains to be had.

[NoelFB]

still certainly a big shift in thinking from OpenGL

Yeah, Foster in general is set up to abstract a lot of that away because it's intended for simple 2D games, but the tradeoff is it doesn't support a lot of the more complex options that a modern 3D rendering API has. I could potentially see a C# library that is more 1-1 with everything SDL provides being pretty cool... I'm not sure if that makes sense for Foster or not, though.

[NoelFB]

Keeping OpenGL is a bit tricky due to the differences in how Uniforms work. Newer APIs tend to just use "Uniform blocks" where you just pass blobs of data for vertex/fragment uniforms and it's up to you to make sure the data matches what the shader expects. Where as OpenGL (or WebGL) combines the shader programs and then has a big list of named Uniforms you're expected to assign individually. I do like the new system a lot more but I'm not sure how to handle this gracefully without having to awkwardly have the user build a table of all their uniforms if they use OpenGL (which I believe is what sokol gfx does)