What the big difference between the OpenGL and D3D renderer? Are they performing and look the same across Windows and Linux? What about MacOS? I guess if it run on Linux I can fiddle with the source and make it run on it?
Look awesome! Always good to have diversity in 3D engine.
I'm using https://github.com/bkaradzic/bgfx for low-level rendering abstraction. IIRC in the engine there is no difference between opengl and d3d other than a projection matrix. On the outside there can be a difference, e.g. if opengl does not support some operation d3d does (because of drivers). On my computer D3D a tiny bit faster than OGL on windows.
I've not tried Linux for a long time, so it's possible there are some issues. But it's definitely compilable and it used to run few months ago.
MacOS port should be easy, there once was a branch with a lot of stuff already ported, but it was done by other programmer and he did not finish it.