DX12 Implementation Details

[adriengivry]

Starting a thread for discussions on DX12 implementation.

[adriengivry]

Answering this comment.

I'd be very happy for you to help with the DX12 implementation! So far we have one collaborator that started background work on DX12, so you might need to discuss with him to avoid overlap.

1. Not at all, the API isn't set is stone. As I mentioned in the README, I expect it to change while new backends get added. I'd be open to move to something as you suggested (BeginRendering), so that could be a nice first work item if you're willing to tackle it.

2. I believe OpenRHI's sempahores and fences can both be a fence in DX12's implementation. I'm not super familiar with DX12, but from what I could gather, DX12 fences seem to be more flexible. This is always something we can iterate on in the future.

Also, I created a branch specifically for DX12: feature/dx12, so feel free to target it for any DX12-specific work.

[RobTOsb]

Alright, I'll just keep a reference to the allocator in the context then and we'll keep it separate, thanks Adrian! It seems to be what they do in NRI too.

[adriengivry]

I think #13 should be ready to merge to feature/dx12 soon, which provides the foundations for the DX12 backend. From there I'll let you and Frank decide how you want to split that up. I believe he suggested that you start with RenderPass, CommandPool, CommandBuffer once it's merged. Or you can base your branch on his branch AQUOSTICS:frank.xu/DirectX12Base and rebase later

[AQUOSTICS]

@RobTOsb hey Robert, quick fyi I just merged the foundation PR to feature/dx12 branch. Feel free to pull latest on that and rebased on top of that.

[RobTOsb]

@AQUOSTICS @adriengivry Hey thanks for your work, I got everything synced now and have got a bit of work done on the render pass class and command classes. I think I'm going to have to heavily rework the code around these though as DX12 is significantly different from vulkan in this kind of usage. For example when starting a render pass you have to pass the CPU handles to the render targets to set them and clear them. However these render targets are allocated from a descriptor heap and there is currently no way of passing a descriptor heap.

I could put the heaps in the framebuffer structure, but that doesn't really make sense to me and the application should probably handle these as well. Its the same with allocating command lists. There is no allocating multiple command lists at once and each command list needs to be associated with an allocator.

So what I'm doing right now is creating the command pool and the command list separately and passing the allocator to the command list, this is less abstract than the current version and maps better to both api's. If a user wants to create multiple command lists at a time and associate them with the same allocator that should be their choice and up to them, not something we choose for them. As for render passes I don't really know what to do as everything feels kind of like a hack to me, I could keep references to the handles from the descriptor heap to the render targets in the render pass itself but that feels wrong as well. What do you guys think? I'm sorry if I am asking too many questions too quickly.

[AQUOSTICS]

I didn't modify RenderPassContext but for dx12 I think you need more data in the context(rtv/dsv descriptor heap, or at least current rtv/dsv). I personally disagree with how dx12 separates command allocator and command list as different objects, but yes as you said we should let user to decide what they want.

[adriengivry]

Following the merging of @AQUOSTICS and @RobTOsb work to feature/dx12, next steps would be to create a branch that integrate the latest changes from main to feature/dx12. Premake files should be removed in lieu of adjusted CMake configuration to support DX12. gen_proj_win32.bat could be renamed to gen_proj_win32_vulkan.bat and a gen_proj_win32_dx12.bat could be added.

[AQUOSTICS]

On it already.

[AQUOSTICS]

Done! @RobTOsb feel free to rebase on latest feature/dx12.

[adriengivry]

Just created the PR for the integration of DX12 feature branch to main.
I've added a bunch of to-do items before integration.

#24