1 files changed, 87 insertions, 0 deletions
diff --git a/source/core/StarTickRateMonitor.cpp b/source/core/StarTickRateMonitor.cpp
new file mode 100644
index 0000000..78a423a
--- /dev/null
+++ b/source/core/StarTickRateMonitor.cpp
@@ -0,0 +1,87 @@
+#include "StarTickRateMonitor.hpp"
+#include "StarTime.hpp"
+
+namespace Star {
+
+TickRateMonitor::TickRateMonitor(double window) : m_window(window) {
+  reset();
+}
+
+double TickRateMonitor::window() const {
+  return m_window;
+}
+
+void TickRateMonitor::reset() {
+  m_lastTick = Time::monotonicTime() - m_window;
+  m_ticks = 0;
+}
+
+double TickRateMonitor::tick(unsigned count) {
+  double currentTime = Time::monotonicTime();
+
+  if (m_lastTick > currentTime) {
+    m_lastTick = currentTime - m_window;
+    m_ticks = 0;
+  } else if (m_lastTick < currentTime) {
+    double timePast = currentTime - m_lastTick;
+    double rate = m_ticks / m_window;
+    m_ticks = max(0.0, m_ticks - timePast * rate);
+    m_lastTick = currentTime;
+  }
+
+  m_ticks += count;
+
+  return m_ticks / m_window;
+}
+
+double TickRateMonitor::rate() const {
+  return TickRateMonitor(*this).tick(0);
+}
+
+TickRateApproacher::TickRateApproacher(double targetTickRate, double window)
+  : m_tickRateMonitor(window), m_targetTickRate(targetTickRate) {}
+
+double TickRateApproacher::window() const {
+  return m_tickRateMonitor.window();
+}
+
+void TickRateApproacher::setWindow(double window) {
+  if (window != m_tickRateMonitor.window()) {
+    m_tickRateMonitor = TickRateMonitor(window);
+    tick(m_targetTickRate * window);
+  }
+}
+
+double TickRateApproacher::targetTickRate() const {
+  return m_targetTickRate;
+}
+
+void TickRateApproacher::setTargetTickRate(double targetTickRate) {
+  m_targetTickRate = targetTickRate;
+}
+
+void TickRateApproacher::reset() {
+  setWindow(window());
+}
+
+double TickRateApproacher::tick(unsigned count) {
+  return m_tickRateMonitor.tick(count);
+}
+
+double TickRateApproacher::rate() const {
+  return m_tickRateMonitor.rate();
+}
+
+double TickRateApproacher::ticksBehind() {
+  return (m_targetTickRate - m_tickRateMonitor.rate()) * window();
+}
+
+double TickRateApproacher::ticksAhead() {
+  return -ticksBehind();
+}
+
+double TickRateApproacher::spareTime() {
+  return ticksAhead() / m_targetTickRate;
+}
+
+}