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1 files changed, 78 insertions, 0 deletions

diff --git a/source/core/StarTickRateMonitor.hpp b/source/core/StarTickRateMonitor.hpp
new file mode 100644
index 0000000..a50ff5e
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+++ b/source/core/StarTickRateMonitor.hpp
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+#ifndef STAR_TICK_RATE_MONITOR_HPP
+#define STAR_TICK_RATE_MONITOR_HPP
+
+#include "StarList.hpp"
+
+namespace Star {
+
+// Monitors the rate at which 'tick()' is called in wall-clock seconds.
+class TickRateMonitor {
+public:
+  // 'window' controls the dropoff at which 'rate' will approach zero if tick
+  // is not called, measured in seconds.
+  TickRateMonitor(double window);
+
+  double window() const;
+
+  // Resets to a zero tick-rate state
+  void reset();
+
+  // Ticks the given number of times, returns the current rate.
+  double tick(unsigned count = 1);
+
+  // Returns the rate as of the *current* time, not the time of the last tick.
+  double rate() const;
+
+private:
+  void dropOff(double currentTime);
+
+  double m_window;
+  double m_lastTick;
+  double m_ticks;
+};
+
+// Helps tick at as close as possible to a given tick rate
+class TickRateApproacher {
+public:
+  TickRateApproacher(double targetTickRate, double window);
+
+  // The TickRateMonitor window influences how long the TickRateApproacher will
+  // try and speed up or slow down the tick rate to match the target tick rate.
+  // It should be chosen so that it is not so short that the actual target rate
+  // drifts, but not too long so that the rate returns to normal quickly enough
+  // with outliers.
+  double window() const;
+  // Setting the window to a new value will reset the TickRateApproacher
+  void setWindow(double window);
+
+  double targetTickRate() const;
+  void setTargetTickRate(double targetTickRate);
+
+  // Resets such that the current tick rate is assumed to be perfectly at the
+  // target.
+  void reset();
+
+  double tick(unsigned count = 1);
+  double rate() const;
+
+  // How many ticks we currently should perform, so that if each tick happened
+  // instantly, we would be as close to the target tick rate as possible.  If
+  // we are ahead, may be negative.
+  double ticksBehind();
+
+  // The negative of ticksBehind, is positive for how many ticks ahead we
+  // currently are.
+  double ticksAhead();
+
+  // How much spare time we have until the tick rate will begin to be behind
+  // the target tick rate.
+  double spareTime();
+
+private:
+  TickRateMonitor m_tickRateMonitor;
+  double m_targetTickRate;
+};
+
+};
+
+#endif