[dxvk] Rework frame rate limiter

src/dxvk/dxvk_presenter.cpp

@@ -672,10 +672,6 @@ 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.
-      applyFrameRateLimit(frame.mode);
-
       // 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).
@@ -687,6 +683,10 @@ namespace dxvk {
           Logger::err(str::format("Presenter: vkWaitForPresentKHR failed: ", vr));
       }
 
+      // Apply the FPS limiter before signaling the frame event in
+      // order to reduce latency if the app uses it for frame pacing.
+      applyFrameRateLimit(frame.mode);
+
       // Always signal even on error, since failures here
       // are transparent to the front-end.
       m_signal->signal(frame.frameId);

src/util/util_fps_limiter.cpp

@@ -35,12 +35,12 @@ namespace dxvk {
     std::lock_guard<dxvk::mutex> lock(m_mutex);
 
     if (!m_envOverride) {
-      m_targetInterval = frameRate > 0.0
-        ? TimerDuration(int64_t(double(TimerDuration::period::den) / frameRate))
-        : TimerDuration::zero();
-
-      if (isEnabled() && !m_initialized)
-        initialize();
+      if (frameRate > 0.0) {
+        m_targetInterval = TimerDuration(int64_t(double(TimerDuration::period::den) / frameRate));
+      } else {
+        m_targetInterval = TimerDuration::zero();
+        m_nextDeadline = TimePoint();
+      }
     }
   }
 
@@ -51,36 +51,18 @@ namespace dxvk {
     if (!isEnabled())
       return;
 
-    auto t0 = m_lastFrame;
-    auto t1 = dxvk::high_resolution_clock::now();
+    TimePoint now = dxvk::high_resolution_clock::now();
 
-    auto frameTime = std::chrono::duration_cast<TimerDuration>(t1 - t0);
+    if (m_nextDeadline == TimePoint())
+      m_nextDeadline = now;
 
-    if (frameTime * 100 > m_targetInterval * 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();
+    if (m_nextDeadline > now) {
+      Sleep::sleepUntil(now, m_nextDeadline);
+      m_nextDeadline += m_targetInterval;
     } 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 = m_targetInterval - 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 - m_targetInterval;
-      m_deviation = std::min(m_deviation, m_targetInterval / 16);
+      uint64_t nFrames = TimerDuration(now - m_nextDeadline).count() / m_targetInterval.count();
+      m_nextDeadline += (1 + nFrames) * m_targetInterval;
     }
-
-    m_lastFrame = t1;
-  }
-
-
-  void FpsLimiter::initialize() {
-    m_lastFrame = dxvk::high_resolution_clock::now();
-    m_initialized = true;
   }
 
 }

src/util/util_fps_limiter.h

@@ -54,14 +54,10 @@ namespace dxvk {
     dxvk::mutex     m_mutex;
 
     TimerDuration   m_targetInterval  = TimerDuration::zero();
-    TimerDuration   m_deviation       = TimerDuration::zero();
-    TimePoint       m_lastFrame;
+    TimePoint       m_nextDeadline    = TimePoint();
 
-    bool            m_initialized     = false;
     bool            m_envOverride     = false;
 
-    void initialize();
-
   };
 
 }