[util] Implement refresh rate heuristic for frame rate limiter

src/util/util_fps_limiter.cpp

@@ -35,49 +35,103 @@ namespace dxvk {
     std::lock_guard<dxvk::mutex> lock(m_mutex);
 
     if (!m_envOverride) {
-      m_targetInterval = frameRate != 0.0
+      TimerDuration interval = frameRate != 0.0
         ? TimerDuration(int64_t(double(TimerDuration::period::den) / frameRate))
         : TimerDuration::zero();
 
-      if (isEnabled() && !m_initialized)
-        initialize();
+      if (m_targetInterval != interval) {
+        m_targetInterval = interval;
+
+        m_heuristicFrameCount = 0;
+        m_heuristicEnable = false;
+
+        if (m_targetInterval != TimerDuration::zero() && !m_initialized)
+          initialize();
+      }
     }
   }
 
 
   void FpsLimiter::delay() {
-    std::lock_guard<dxvk::mutex> lock(m_mutex);
+    std::unique_lock<dxvk::mutex> lock(m_mutex);
+    auto interval = m_targetInterval;
 
-    if (!isEnabled())
+    if (interval == TimerDuration::zero())
       return;
 
     auto t0 = m_lastFrame;
     auto t1 = dxvk::high_resolution_clock::now();
 
+    if (interval < TimerDuration::zero()) {
+      interval = -interval;
+
+      if (!testRefreshHeuristic(interval, t1))
+        return;
+    }
+
+    // Subsequent code must not access any class members
+    // that can be written by setTargetFrameRate
+    lock.unlock();
+
     auto frameTime = std::chrono::duration_cast<TimerDuration>(t1 - t0);
 
-    if (frameTime * 100 > m_targetInterval * 103 - m_deviation * 100) {
+    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 = m_targetInterval - m_deviation - frameTime;
+      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 - m_targetInterval;
-      m_deviation = std::min(m_deviation, m_targetInterval / 16);
+      m_deviation += frameTime - interval;
+      m_deviation = std::min(m_deviation, interval / 16);
     }
 
     m_lastFrame = t1;
   }
 
 
+  bool FpsLimiter::testRefreshHeuristic(TimerDuration interval, TimePoint now) {
+    if (m_heuristicEnable)
+      return true;
+
+    // Use a sliding window to determine whether the current
+    // frame rate is higher than the targeted refresh rate
+    uint32_t heuristicWindow = m_heuristicFrameTimes.size();
+    auto windowStart = m_heuristicFrameTimes[m_heuristicFrameCount % heuristicWindow];
+    auto windowDuration = std::chrono::duration_cast<TimerDuration>(now - windowStart);
+
+    m_heuristicFrameTimes[m_heuristicFrameCount % heuristicWindow] = now;
+    m_heuristicFrameCount += 1;
+
+    // The first window of frames may contain faster frames as the
+    // internal swap chain queue fills up, so we should ignore it.
+    if (m_heuristicFrameCount < 2 * heuristicWindow)
+      return false;
+
+    // Test whether we should engage the frame rate limiter. It will
+    // stay enabled until the refresh rate or vsync enablement change.
+    m_heuristicEnable = (103 * windowDuration) < (100 * heuristicWindow) * interval;
+
+    if (m_heuristicEnable) {
+      double got = (double(heuristicWindow) * double(TimerDuration::period::den))
+                 / (double(windowDuration.count()) * double(TimerDuration::period::num));
+      double refresh = double(TimerDuration::period::den) / (double(TimerDuration::period::num) * double(interval.count()));
+
+      Logger::info(str::format("Detected frame rate (~", uint32_t(got), ") higher than selected refresh rate of ~",
+        uint32_t(refresh), " Hz.\n", "Engaging frame rate limiter."));
+    }
+
+    return m_heuristicEnable;
+  }
+
+
   void FpsLimiter::initialize() {
     m_lastFrame = dxvk::high_resolution_clock::now();
     m_initialized = true;

src/util/util_fps_limiter.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <array>
+
 #include "thread.h"
 #include "util_time.h"
 
@@ -37,14 +39,6 @@ namespace dxvk {
      */
     void delay();
 
-    /**
-     * \brief Checks whether the frame rate limiter is enabled
-     * \returns \c true if the target frame rate is non-zero.
-     */
-    bool isEnabled() const {
-      return m_targetInterval != TimerDuration::zero();
-    }
-
   private:
 
     using TimePoint = dxvk::high_resolution_clock::time_point;
@@ -54,11 +48,17 @@ namespace dxvk {
 
     TimerDuration   m_targetInterval  = TimerDuration::zero();
     TimerDuration   m_deviation       = TimerDuration::zero();
-    TimePoint       m_lastFrame;
+    TimePoint       m_lastFrame       = TimePoint();
 
     bool            m_initialized     = false;
     bool            m_envOverride     = false;
 
+    uint32_t                  m_heuristicFrameCount = 0;
+    std::array<TimePoint, 16> m_heuristicFrameTimes = { };
+    bool                      m_heuristicEnable = false;
+
+    bool testRefreshHeuristic(TimerDuration interval, TimePoint now);
+
     void initialize();
 
   };