Add a VsyncSource for renderers that already block for V-sync

app/app.pro

@@ -116,12 +116,15 @@ ffmpeg {
     SOURCES += \
         streaming/video/ffmpeg.cpp \
         streaming/video/ffmpeg-renderers/sdl.cpp \
-        streaming/video/ffmpeg-renderers/pacer/pacer.cpp
+        streaming/video/ffmpeg-renderers/pacer/pacer.cpp \
+        streaming/video/ffmpeg-renderers/pacer/nullthreadedvsyncsource.cpp
+
 
     HEADERS += \
         streaming/video/ffmpeg.h \
         streaming/video/ffmpeg-renderers/renderer.h \
-        streaming/video/ffmpeg-renderers/pacer/pacer.h
+        streaming/video/ffmpeg-renderers/pacer/pacer.h \
+        streaming/video/ffmpeg-renderers/pacer/nullthreadedvsyncsource.h
 }
 libva {
     message(VAAPI renderer selected)

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

@@ -0,0 +1,42 @@
+#include "nullthreadedvsyncsource.h"
+
+NullThreadedVsyncSource::NullThreadedVsyncSource(Pacer* pacer) :
+    m_Pacer(pacer),
+    m_Thread(nullptr)
+{
+    SDL_AtomicSet(&m_Stopping, 0);
+}
+
+NullThreadedVsyncSource::~NullThreadedVsyncSource()
+{
+    if (m_Thread != nullptr) {
+        SDL_AtomicSet(&m_Stopping, 1);
+        SDL_WaitThread(m_Thread, nullptr);
+    }
+}
+
+bool NullThreadedVsyncSource::initialize(SDL_Window*)
+{
+    m_Thread = SDL_CreateThread(vsyncThread, "Null 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 NullThreadedVsyncSource::vsyncThread(void* context)
+{
+    NullThreadedVsyncSource* me = reinterpret_cast<NullThreadedVsyncSource*>(context);
+
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
+
+    while (SDL_AtomicGet(&me->m_Stopping) == 0) {
+        me->m_Pacer->vsyncCallback();
+    }
+
+    return 0;
+}

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

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