Add PoC VsyncSource for Windows using DwmFlush(). Soon to be replaced with D3DKMTWaitForVerticalBlankEvent().

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.cpp

@@ -0,0 +1,49 @@
+#include "dxvsyncsource.h"
+
+#include <dwmapi.h>
+
+DxVsyncSource::DxVsyncSource(Pacer* pacer) :
+    m_Pacer(pacer),
+    m_Thread(nullptr)
+{
+    SDL_AtomicSet(&m_Stopping, 0);
+}
+
+DxVsyncSource::~DxVsyncSource()
+{
+    if (m_Thread != nullptr) {
+        SDL_AtomicSet(&m_Stopping, 1);
+        SDL_WaitThread(m_Thread, nullptr);
+    }
+}
+
+bool DxVsyncSource::initialize(SDL_Window* window)
+{
+    m_Thread = SDL_CreateThread(vsyncThread, "DX Vsync Thread", this);
+    if (m_Thread == nullptr) {
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                     "Unable to create DX V-sync thread: %s",
+                     SDL_GetError());
+        return false;
+    }
+
+    return true;
+}
+
+int DxVsyncSource::vsyncThread(void* context)
+{
+    DxVsyncSource* me = reinterpret_cast<DxVsyncSource*>(context);
+
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
+
+    while (SDL_AtomicGet(&me->m_Stopping) == 0) {
+        // FIXME: We should really use D3DKMTWaitForVerticalBlankEvent() instead!
+        // https://bugs.chromium.org/p/chromium/issues/detail?id=467617
+        // https://chromium.googlesource.com/chromium/src.git/+/c564f2fe339b2b2abb0c8773c90c83215670ea71/gpu/ipc/service/gpu_vsync_provider_win.cc
+        DwmFlush();
+
+        me->m_Pacer->vsyncCallback();
+    }
+
+    return 0;
+}

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "pacer.h"
+
+class DxVsyncSource : public IVsyncSource
+{
+public:
+    DxVsyncSource(Pacer* pacer);
+
+    virtual ~DxVsyncSource();
+
+    virtual bool initialize(SDL_Window* window);
+
+private:
+    static int vsyncThread(void* context);
+
+    Pacer* m_Pacer;
+    SDL_Thread* m_Thread;
+    SDL_atomic_t m_Stopping;
+};

app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp

@@ -4,6 +4,10 @@
 #include "displaylinkvsyncsource.h"
 #endif
 
+#ifdef Q_OS_WIN32
+#include "dxvsyncsource.h"
+#endif
+
 #define FRAME_HISTORY_ENTRIES 8
 
 Pacer::Pacer(IVsyncRenderer* renderer) :
@@ -18,9 +22,6 @@ Pacer::Pacer(IVsyncRenderer* renderer) :
 
 Pacer::~Pacer()
 {
-    // Stop V-sync callbacks
-    delete m_VsyncSource;
-
     drain();
 }
 
@@ -105,8 +106,10 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps)
                 "Frame pacing: target %d Hz with %d FPS stream",
                 m_DisplayFps, m_MaxVideoFps);
 
-#ifdef Q_OS_DARWIN
+#if defined(Q_OS_DARWIN)
     m_VsyncSource = new DisplayLinkVsyncSource(this);
+#elif defined(Q_OS_WIN32)
+    m_VsyncSource = new DxVsyncSource(this);
 #else
     SDL_assert(false);
 #endif
@@ -126,6 +129,10 @@ void Pacer::submitFrame(AVFrame* frame)
 
 void Pacer::drain()
 {
+    // Stop V-sync callbacks
+    delete m_VsyncSource;
+    m_VsyncSource = nullptr;
+
     while (!m_FrameQueue.isEmpty()) {
         AVFrame* frame = m_FrameQueue.dequeue();
         av_frame_free(&frame);