How to handle multiple DirectX devices

[docEdub]

I'm working with @bghgary on a project that uses multiple DirectX devices in the same process. Is there a way to do this with bgfx? If not, then how difficult would it be for us to implement? Is it so far outside the scope of what bgfx does currently that changing it to handle multiple devices would be a large undertaking? ...or would it be relatively simple? We're happy to create a PR if it's relatively simple.

[bkaradzic]

bgfx doesn't support this at all right now.

What style multiple devices?

Sharing workload, different workload, etc.?

[bghgary]

One scenario is being able to render to two different screens with different GPUs (e.g., multi-monitor situations). It could be shared workload or different workload.

[bkaradzic]

Shared workload is simpler since then all could be internal, and internally it would flip-flop device workload between two GPUs at different frames, and all resources would uploaded to both GPUs.

Different workloads on GPUs is more complex to implement, because all Resource APIs and submit/dispatch Encoder APIs would have to get node mask (as in D3D12 terminology) parameter, and then sharing between GPUs need to support transfer.

I wanted to implement this for long time, where for example integrated GPU could be used for tasks like occlusion culling, and discrete GPU could be used for main rendering, but never got around it.

I have no ETA for this.

[bghgary]

I think we might be able to get away with shared workload and just render part of the workload depending on the target. We can help with the implementation if you have time to guide us.

[docEdub]

We'd like to move on this ASAP, so any advice on how we can contribute would be appreciated. 🙏

[bkaradzic]

You could just hack whatever you need into your fork. No need to contribute back at this moment.