D3D12: implement backend

[oviano]

Hello @floooh

Long-time sokol user here. Thanks for the great library!

I know you've mentioned D3D12 is better suited for sokol_gfx2. That said, I had a need for it and have a complete implementation that passes all samples. Offering it in case it's useful, with no expectation to merge.

Even if it's not right for mainline, others may find it helpful?

Summary

• Full D3D12 backend implementation for sokol_gfx.h
• Supports all existing sokol features including compute shaders
• Passes all unit tests and samples (d3d12-specific samples in separate sokol-samples PR)
• Shader compilation via d3dcompiler_47.dll (same approach as D3D11)
• Performance: ~5-25% faster than D3D11 depending on workload

Design

The implementation follows D3D12 best practices rather than being a thin wrapper over D3D11 patterns:

• Double-buffered frames - per-frame command allocators for CPU/GPU overlap
• Fence-based synchronization - application provides fence via sg_environment
• Root signatures - per-pipeline, using descriptor tables and root CBVs
• Pipeline state objects - full PSO with caching and deferred release
• Descriptor heaps - CPU-side for creation, GPU-visible for binding (configurable sizes)
• Uniform buffer ring - per-frame with 256-byte alignment
• Upload ring buffer - per-frame staging for image updates
• Resource barriers - automatic state tracking and transitions
• Deferred release queue - fence-based safe resource cleanup

Written in C99-compatible style consistent with the other backends.

Implementation size: ~4,600 lines (compared to D3D11's ~2,300 lines). The larger size reflects D3D12's explicit resource management model.

Changes

• sokol_gfx.h - D3D12 backend implementation
• sokol_app.h - D3D12 swapchain/window integration
• sokol_glue.h - D3D12 environment/swapchain helpers
• util/sokol_*.h - D3D12 support in utility headers
• tests/ - D3D12 test configurations and presets

Testing

• All 322 unit tests pass (Debug)
• Static analysis clean (clang --analyze)
• Tested on Windows with NVIDIA RTX 3060

Note

The language binding examples (sokol-odin, sokol-rust, etc.) will need their switch/match statements updated to handle the new D3D12 backend case.

Related PRs

floooh/sokol-samples#188
floooh/sokol-tools#206

[floooh]

Impressive work, but this is too big to review/merge (as you expected though ;)

I'll keep the PR open though for other people to reference, and maybe also as reference for a time when an official D3D12 backend might be implemented.

PS: when I got some more time I'll try to play around with the PR a bit. E.g. when the performance is comparable to the D3D11 backend, that might be a good reason to start thinking about replacing the D3D11 backend with D3D12 - mainly because D3D12 has a more modern shader compiler infrastructure...

[floooh]

PS: the failing CI is about missing switch-prongs for a switch on the backend enum in some of the language samples... nothing critical.

[oviano]

Yup, all understood and that makes sense.

Essentially...use it as you see fit (or not!).

[oviano]

I added my stress test to a new branch, which might be useful if/when you come to experiment.

https://github.com/oviano/sokol/tree/d3d12-backend-with-stress-test