Backends: DX12: Let user specifies the backbuffer count by setting ImGui_ImplDX12_InitInfo::BackBuffer and add support for a single frame in flight. #9035
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…itInfo::BackBuffer and add support for a single frame in flight
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With this change the waitable object latency is tied to |
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Frames in flight can improve and stabilize the framerate, but they may also introduce some input lag, because frames are buffered ahead of time. Allowing the user to set just one frame in flight, effectively disabling frame queuing, can be useful in scenarios where minimizing input latency is more important than maximizing throughput.
Currently, if the user specify only one frame in flight, the DX12 backend crashes. Just to be clear, this is not a regression introduced by #8961, it was already present beforehand.
The crash occurs because, unlike the example implementation, the backend links the back buffer count directly to the number of frames in flight. If you set 1 frame in flight, the backend will use 1 backbuffer, but DXGI_SWAP_EFFECT_FLIP_DISCARD requires at least 2 back buffers, causing the swapchain creation to fail.
To fix this, it was necessary to decouple the back buffer count from the frame in flight count. The back buffer related members have been moved from ImGui_ImplDX12_FrameContext to a new structure, ImGui_ImplDX12_Backbuffer, allowing each to have a different count. I also added a BackBuffer field to ImGui_ImplDX12_InitInfo so users can configure it explicitly.