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;
+}