1 files changed, 179 insertions, 0 deletions
diff --git a/support/hololens/ServoApp/Common/StepTimer.h b/support/hololens/ServoApp/Common/StepTimer.h
new file mode 100644
index 00000000000..36102d680db
--- /dev/null
+++ b/support/hololens/ServoApp/Common/StepTimer.h
@@ -0,0 +1,179 @@
+#pragma once
+
+namespace DX {
+// Helper class for animation and simulation timing.
+class StepTimer {
+public:
+  StepTimer()
+      : m_elapsedTicks(0), m_totalTicks(0), m_leftOverTicks(0), m_frameCount(0),
+        m_framesPerSecond(0), m_framesThisSecond(0), m_qpcSecondCounter(0),
+        m_isFixedTimeStep(false), m_targetElapsedTicks(TicksPerSecond / 60) {
+    m_qpcFrequency = GetPerformanceFrequency();
+
+    // Initialize max delta to 1/10 of a second.
+    m_qpcMaxDelta = m_qpcFrequency / 10;
+  }
+
+  // Get elapsed time since the previous Update call.
+  uint64_t GetElapsedTicks() const { return m_elapsedTicks; }
+  double GetElapsedSeconds() const { return TicksToSeconds(m_elapsedTicks); }
+
+  // Get total time since the start of the program.
+  uint64_t GetTotalTicks() const { return m_totalTicks; }
+  double GetTotalSeconds() const { return TicksToSeconds(m_totalTicks); }
+
+  // Get total number of updates since start of the program.
+  uint32_t GetFrameCount() const { return m_frameCount; }
+
+  // Get the current framerate.
+  uint32_t GetFramesPerSecond() const { return m_framesPerSecond; }
+
+  // Set whether to use fixed or variable timestep mode.
+  void SetFixedTimeStep(bool isFixedTimestep) {
+    m_isFixedTimeStep = isFixedTimestep;
+  }
+
+  // Set how often to call Update when in fixed timestep mode.
+  void SetTargetElapsedTicks(uint64_t targetElapsed) {
+    m_targetElapsedTicks = targetElapsed;
+  }
+  void SetTargetElapsedSeconds(double targetElapsed) {
+    m_targetElapsedTicks = SecondsToTicks(targetElapsed);
+  }
+
+  // Integer format represents time using 10,000,000 ticks per second.
+  static const uint64_t TicksPerSecond = 10'000'000;
+
+  static double TicksToSeconds(uint64_t ticks) {
+    return static_cast<double>(ticks) / TicksPerSecond;
+  }
+  static uint64_t SecondsToTicks(double seconds) {
+    return static_cast<uint64_t>(seconds * TicksPerSecond);
+  }
+
+  // Convenient wrapper for QueryPerformanceFrequency. Throws an exception if
+  // the call to QueryPerformanceFrequency fails.
+  static inline uint64_t GetPerformanceFrequency() {
+    LARGE_INTEGER freq;
+    if (!QueryPerformanceFrequency(&freq)) {
+      winrt::throw_last_error();
+    }
+    return freq.QuadPart;
+  }
+
+  // Gets the current number of ticks from QueryPerformanceCounter. Throws an
+  // exception if the call to QueryPerformanceCounter fails.
+  static inline int64_t GetTicks() {
+    LARGE_INTEGER ticks;
+    if (!QueryPerformanceCounter(&ticks)) {
+      winrt::throw_last_error();
+    }
+    return ticks.QuadPart;
+  }
+
+  // After an intentional timing discontinuity (for instance a blocking IO
+  // operation) call this to avoid having the fixed timestep logic attempt a set
+  // of catch-up Update calls.
+
+  void ResetElapsedTime() {
+    m_qpcLastTime = GetTicks();
+
+    m_leftOverTicks = 0;
+    m_framesPerSecond = 0;
+    m_framesThisSecond = 0;
+    m_qpcSecondCounter = 0;
+  }
+
+  // Update timer state, calling the specified Update function the appropriate
+  // number of times.
+  template <typename TUpdate> void Tick(const TUpdate &update) {
+    // Query the current time.
+    uint64_t currentTime = GetTicks();
+    uint64_t timeDelta = currentTime - m_qpcLastTime;
+
+    m_qpcLastTime = currentTime;
+    m_qpcSecondCounter += timeDelta;
+
+    // Clamp excessively large time deltas (e.g. after paused in the debugger).
+    if (timeDelta > m_qpcMaxDelta) {
+      timeDelta = m_qpcMaxDelta;
+    }
+
+    // Convert QPC units into a canonical tick format. This cannot overflow due
+    // to the previous clamp.
+    timeDelta *= TicksPerSecond;
+    timeDelta /= m_qpcFrequency;
+
+    uint32_t lastFrameCount = m_frameCount;
+
+    if (m_isFixedTimeStep) {
+      // Fixed timestep update logic
+
+      // If the app is running very close to the target elapsed time (within 1/4
+      // of a millisecond) just clamp the clock to exactly match the target
+      // value. This prevents tiny and irrelevant errors from accumulating over
+      // time. Without this clamping, a game that requested a 60 fps fixed
+      // update, running with vsync enabled on a 59.94 NTSC display, would
+      // eventually accumulate enough tiny errors that it would drop a frame. It
+      // is better to just round small deviations down to zero to leave things
+      // running smoothly.
+
+      if (abs(static_cast<int64_t>(timeDelta - m_targetElapsedTicks)) <
+          TicksPerSecond / 4000) {
+        timeDelta = m_targetElapsedTicks;
+      }
+
+      m_leftOverTicks += timeDelta;
+
+      while (m_leftOverTicks >= m_targetElapsedTicks) {
+        m_elapsedTicks = m_targetElapsedTicks;
+        m_totalTicks += m_targetElapsedTicks;
+        m_leftOverTicks -= m_targetElapsedTicks;
+        m_frameCount++;
+
+        update();
+      }
+    } else {
+      // Variable timestep update logic.
+      m_elapsedTicks = timeDelta;
+      m_totalTicks += timeDelta;
+      m_leftOverTicks = 0;
+      m_frameCount++;
+
+      update();
+    }
+
+    // Track the current framerate.
+    if (m_frameCount != lastFrameCount) {
+      m_framesThisSecond++;
+    }
+
+    if (m_qpcSecondCounter >= static_cast<uint64_t>(m_qpcFrequency)) {
+      m_framesPerSecond = m_framesThisSecond;
+      m_framesThisSecond = 0;
+      m_qpcSecondCounter %= m_qpcFrequency;
+    }
+  }
+
+private:
+  // Source timing data uses QPC units.
+  uint64_t m_qpcFrequency;
+  uint64_t m_qpcLastTime;
+  uint64_t m_qpcMaxDelta;
+
+  // Derived timing data uses a canonical tick format.
+  uint64_t m_elapsedTicks;
+  uint64_t m_totalTicks;
+  uint64_t m_leftOverTicks;
+
+  // Members for tracking the framerate.
+  uint32_t m_frameCount;
+  uint32_t m_framesPerSecond;
+  uint32_t m_framesThisSecond;
+  uint64_t m_qpcSecondCounter;
+
+  // Members for configuring fixed timestep mode.
+  bool m_isFixedTimeStep;
+  uint64_t m_targetElapsedTicks;
+};
+} // namespace DX