[util,dxvk] Limit frame rate based on deadline

This should work better now that present_wait is universally supported.

src/dxvk/dxvk_presenter.cpp

@@ -667,10 +667,6 @@ namespace dxvk {
       if (!frame.frameId)
         return;
 
-      // Apply the FPS limiter before signaling the frame event in
-      // order to reduce latency if the app uses it for frame pacing.
-      m_fpsLimiter.delay();
-
       // If the present operation has succeeded, actually wait for it to complete.
       // Don't bother with it on MAILBOX / IMMEDIATE modes since doing so would
       // restrict us to the display refresh rate on some platforms (XWayland).
@@ -685,6 +681,9 @@ namespace dxvk {
       // Always signal even on error, since failures here
       // are transparent to the front-end.
       m_signal->signal(frame.frameId);
+
+      // Apply FPS limtier here to align it as closely with scanout as we can.
+      m_fpsLimiter.delay();
     }
   }
 

src/util/util_fps_limiter.cpp

@@ -44,9 +44,6 @@ namespace dxvk {
 
         m_heuristicFrameCount = 0;
         m_heuristicEnable = false;
-
-        if (m_targetInterval != TimerDuration::zero() && !m_initialized)
-          initialize();
       }
     }
   }
@@ -56,10 +53,11 @@ namespace dxvk {
     std::unique_lock<dxvk::mutex> lock(m_mutex);
     auto interval = m_targetInterval;
 
-    if (interval == TimerDuration::zero())
+    if (interval == TimerDuration::zero()) {
+      m_nextFrame = TimePoint();
       return;
+    }
 
-    auto t0 = m_lastFrame;
     auto t1 = dxvk::high_resolution_clock::now();
 
     if (interval < TimerDuration::zero()) {
@@ -73,27 +71,12 @@ namespace dxvk {
     // that can be written by setTargetFrameRate
     lock.unlock();
 
-    auto frameTime = std::chrono::duration_cast<TimerDuration>(t1 - t0);
-
-    if (frameTime * 100 > interval * 103 - m_deviation * 100) {
-      // If we have a slow frame, reset the deviation since we
-      // do not want to compensate for low performance later on
-      m_deviation = TimerDuration::zero();
-    } else {
-      // Don't call sleep if the amount of time to sleep is shorter
-      // than the time the function calls are likely going to take
-      TimerDuration sleepDuration = interval - m_deviation - frameTime;
-      t1 = Sleep::sleepFor(t1, sleepDuration);
-
-      // Compensate for any sleep inaccuracies in the next frame, and
-      // limit cumulative deviation in order to avoid stutter in case we
-      // have a number of slow frames immediately followed by a fast one.
-      frameTime = std::chrono::duration_cast<TimerDuration>(t1 - t0);
-      m_deviation += frameTime - interval;
-      m_deviation = std::min(m_deviation, interval / 16);
-    }
+    if (t1 < m_nextFrame)
+      Sleep::sleepUntil(t1, m_nextFrame);
 
-    m_lastFrame = t1;
+    m_nextFrame = (t1 < m_nextFrame + interval)
+      ? m_nextFrame + interval
+      : t1 + interval;
   }
 
 
@@ -131,10 +114,4 @@ namespace dxvk {
     return m_heuristicEnable;
   }
 
-
-  void FpsLimiter::initialize() {
-    m_lastFrame = dxvk::high_resolution_clock::now();
-    m_initialized = true;
-  }
-
 }

src/util/util_fps_limiter.h

@@ -47,10 +47,8 @@ namespace dxvk {
     dxvk::mutex     m_mutex;
 
     TimerDuration   m_targetInterval  = TimerDuration::zero();
-    TimerDuration   m_deviation       = TimerDuration::zero();
-    TimePoint       m_lastFrame       = TimePoint();
+    TimePoint       m_nextFrame       = TimePoint();
 
-    bool            m_initialized     = false;
     bool            m_envOverride     = false;
 
     uint32_t                  m_heuristicFrameCount = 0;
@@ -59,8 +57,6 @@ namespace dxvk {
 
     bool testRefreshHeuristic(TimerDuration interval, TimePoint now);
 
-    void initialize();
-
   };
 
 }