From fd563726f02427621dce3ca44ede689c2942890d Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Fri, 15 Apr 2022 23:21:52 -0500
Subject: [PATCH] Fix blocking presents in borderless windowed flip modes

---
 .../video/ffmpeg-renderers/dxva2.cpp          | 35 ++++++++-----------
 1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/app/streaming/video/ffmpeg-renderers/dxva2.cpp b/app/streaming/video/ffmpeg-renderers/dxva2.cpp
index d061c06b..828e1fc8 100644
--- a/app/streaming/video/ffmpeg-renderers/dxva2.cpp
+++ b/app/streaming/video/ffmpeg-renderers/dxva2.cpp
@@ -602,20 +602,10 @@ bool DXVA2Renderer::initializeDevice(SDL_Window* window, bool enableVsync)
         // to reduce latency by avoiding double v-syncing.
         d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
 
-        // If V-sync is enabled (not rendering faster than display),
-        // we can use FlipEx for more efficient swapping.
-        if (enableVsync) {
-            // D3DSWAPEFFECT_FLIPEX requires at least 2 back buffers to allow us to
-            // continue while DWM is waiting to render the surface to the display.
-            d3dpp.SwapEffect = D3DSWAPEFFECT_FLIPEX;
-            d3dpp.BackBufferCount = 2;
-        }
-        else {
-            // With V-sync off, we won't use FlipEx because that will block while
-            // DWM is waiting to render our surface (effectively behaving like V-Sync).
-            d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
-            d3dpp.BackBufferCount = 1;
-        }
+        // D3DSWAPEFFECT_FLIPEX requires at least 2 back buffers to allow us to
+        // continue while DWM is waiting to render the surface to the display.
+        d3dpp.SwapEffect = D3DSWAPEFFECT_FLIPEX;
+        d3dpp.BackBufferCount = 2;
 
         m_BlockingPresent = false;
 
@@ -679,12 +669,17 @@ bool DXVA2Renderer::initializeDevice(SDL_Window* window, bool enableVsync)
         return false;
     }
 
-    hr = m_Device->SetMaximumFrameLatency(1);
-    if (FAILED(hr)) {
-        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
-                     "SetMaximumFrameLatency() failed: %x",
-                     hr);
-        return false;
+    // We must not call this for flip swapchains. It will counterintuitively
+    // increase latency by forcing our Present() to block on DWM even when
+    // using D3DPRESENT_INTERVAL_IMMEDIATE.
+    if (d3dpp.SwapEffect != D3DSWAPEFFECT_FLIPEX) {
+        hr = m_Device->SetMaximumFrameLatency(1);
+        if (FAILED(hr)) {
+            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                         "SetMaximumFrameLatency() failed: %x",
+                         hr);
+            return false;
+        }
     }
 
     return true;