From 1e825c85e5b03c7d435799dbc497b9a64ee14e4f Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Mon, 19 Jan 2026 18:38:38 -0600
Subject: [PATCH] Optimize render to decode fence usage to reduce pipeline
 bubbles

---
 .../video/ffmpeg-renderers/d3d11va.cpp          | 17 ++++++++++++-----
 app/streaming/video/ffmpeg-renderers/d3d11va.h  |  3 ++-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/app/streaming/video/ffmpeg-renderers/d3d11va.cpp b/app/streaming/video/ffmpeg-renderers/d3d11va.cpp
index edcd827d..bcc6ffbb 100644
--- a/app/streaming/video/ffmpeg-renderers/d3d11va.cpp
+++ b/app/streaming/video/ffmpeg-renderers/d3d11va.cpp
@@ -226,12 +226,13 @@ bool D3D11VARenderer::setupSharedDevice(IDXGIAdapter1* adapter)
     }
 
     // Create our decode->render fence
-    m_DecodeRenderSyncFenceValue = 1;
+    m_D2RFenceValue = 1;
     if (!createSharedFencePair(0, m_DecodeDevice.Get(), m_RenderDevice.Get(), m_DecodeD2RFence, m_RenderD2RFence)) {
         goto Exit;
     }
 
     // Create our render->decode fence
+    m_R2DFenceValue = 1;
     if (!createSharedFencePair(0, m_DecodeDevice.Get(), m_RenderDevice.Get(), m_DecodeR2DFence, m_RenderR2DFence)) {
         goto Exit;
     }
@@ -992,8 +993,8 @@ void D3D11VARenderer::renderVideo(AVFrame* frame)
         SDL_assert(m_RenderD2RFence);
 
         lockContext(this);
-        if (SUCCEEDED(m_DecodeDeviceContext->Signal(m_DecodeD2RFence.Get(), m_DecodeRenderSyncFenceValue))) {
-            m_RenderDeviceContext->Wait(m_RenderD2RFence.Get(), m_DecodeRenderSyncFenceValue++);
+        if (SUCCEEDED(m_DecodeDeviceContext->Signal(m_DecodeD2RFence.Get(), m_D2RFenceValue))) {
+            m_RenderDeviceContext->Wait(m_RenderD2RFence.Get(), m_D2RFenceValue++);
         }
         unlockContext(this);
     }
@@ -1046,10 +1047,16 @@ void D3D11VARenderer::renderVideo(AVFrame* frame)
         SDL_assert(m_DecodeR2DFence);
         SDL_assert(m_RenderR2DFence);
 
-        if (SUCCEEDED(m_RenderDeviceContext->Signal(m_RenderR2DFence.Get(), m_DecodeRenderSyncFenceValue))) {
+        // Because Pacer keeps a reference to the current frame until the next frame is rendered,
+        // we insert a wait for the previous frame's fence value rather than the current one.
+        // This means the fence should generally not cause a pipeline bubble for the decoder
+        // unless rendering is taking much longer than expected.
+        if (SUCCEEDED(m_RenderDeviceContext->Signal(m_RenderR2DFence.Get(), m_R2DFenceValue))) {
             lockContext(this);
-            m_DecodeDeviceContext->Wait(m_DecodeR2DFence.Get(), m_DecodeRenderSyncFenceValue++);
+            SDL_assert(m_R2DFenceValue > 0);
+            m_DecodeDeviceContext->Wait(m_DecodeR2DFence.Get(), m_R2DFenceValue - 1);
             unlockContext(this);
+            m_R2DFenceValue++;
         }
     }
 }
diff --git a/app/streaming/video/ffmpeg-renderers/d3d11va.h b/app/streaming/video/ffmpeg-renderers/d3d11va.h
index 72db9846..80ea6781 100644
--- a/app/streaming/video/ffmpeg-renderers/d3d11va.h
+++ b/app/streaming/video/ffmpeg-renderers/d3d11va.h
@@ -79,8 +79,9 @@ private:
 
     SupportedFenceType m_FenceType;
     Microsoft::WRL::ComPtr<ID3D11Fence> m_DecodeD2RFence, m_RenderD2RFence;
+    UINT64 m_D2RFenceValue;
     Microsoft::WRL::ComPtr<ID3D11Fence> m_DecodeR2DFence, m_RenderR2DFence;
-    UINT64 m_DecodeRenderSyncFenceValue;
+    UINT64 m_R2DFenceValue;
     SDL_mutex* m_ContextLock;
     bool m_BindDecoderOutputTextures;