The D3D12 capture path grabbed GetBuffer(0) every Present. Unlike D3D11
flip-model -- where DXGI keeps GetBuffer(0) pointing at the live back
buffer -- D3D12 rotates buffers explicitly: the game renders into the
buffer at GetCurrentBackBufferIndex(), which advances each Present. So
buffer 0 only holds fresh content every Nth frame; the rest copied a
stale buffer, and the mirror silently ran at refresh/N with duplicate
frames in between.
Every metric read full rate (Present counter, published FPS, generation
bump, capture->display latency) because they count Presents, not unique
content -- which is why it looked fine but felt like missing frames,
especially on high-refresh DX12 games (DMC5/Myst at 144, Miles Morales).
Query IDXGISwapChain3::GetCurrentBackBufferIndex() before the trampoline
Present (so it's the just-rendered buffer) and copy that one; fall back
to 0 only if the interface is unavailable. The DX11 path is unaffected.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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