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

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;
+}