1 files changed, 71 insertions, 0 deletions
diff --git a/main/timer_sync.h b/main/timer_sync.h
new file mode 100644
index 0000000000..6ef4254270
--- /dev/null
+++ b/main/timer_sync.h
@@ -0,0 +1,71 @@
+#ifndef TIMER_SYNC_H
+#define TIMER_SYNC_H
+
+#include "core/engine.h"
+
+struct MainFrameTime {
+	float idle_step; // time to advance idles for (argument to process())
+	int physics_steps; // number of times to iterate the physics engine
+
+	void clamp_idle(float min_idle_step, float max_idle_step);
+};
+
+class MainTimerSync {
+	// wall clock time measured on the main thread
+	uint64_t last_cpu_ticks_usec;
+	uint64_t current_cpu_ticks_usec;
+
+	// logical game time since last physics timestep
+	float time_accum;
+
+	// current difference between wall clock time and reported sum of idle_steps
+	float time_deficit;
+
+	// number of frames back for keeping accumulated physics steps roughly constant.
+	// value of 12 chosen because that is what is required to make 144 Hz monitors
+	// behave well with 60 Hz physics updates. The only worse commonly available refresh
+	// would be 85, requiring CONTROL_STEPS = 17.
+	static const int CONTROL_STEPS = 12;
+
+	// sum of physics steps done over the last (i+1) frames
+	int accumulated_physics_steps[CONTROL_STEPS];
+
+	// typical value for accumulated_physics_steps[i] is either this or this plus one
+	int typical_physics_steps[CONTROL_STEPS];
+
+	int fixed_fps;
+
+protected:
+	// returns the fraction of p_frame_slice required for the timer to overshoot
+	// before advance_core considers changing the physics_steps return from
+	// the typical values as defined by typical_physics_steps
+	float get_physics_jitter_fix();
+
+	// gets our best bet for the average number of physics steps per render frame
+	// return value: number of frames back this data is consistent
+	int get_average_physics_steps(float &p_min, float &p_max);
+
+	// advance physics clock by p_idle_step, return appropriate number of steps to simulate
+	MainFrameTime advance_core(float p_frame_slice, int p_iterations_per_second, float p_idle_step);
+
+	// calls advance_core, keeps track of deficit it adds to animaption_step, make sure the deficit sum stays close to zero
+	MainFrameTime advance_checked(float p_frame_slice, int p_iterations_per_second, float p_idle_step);
+
+	// determine wall clock step since last iteration
+	float get_cpu_idle_step();
+
+public:
+	MainTimerSync();
+
+	// start the clock
+	void init(uint64_t p_cpu_ticks_usec);
+	// set measured wall clock time
+	void set_cpu_ticks_usec(uint64_t p_cpu_ticks_usec);
+	//set fixed fps
+	void set_fixed_fps(int p_fixed_fps);
+
+	// advance one frame, return timesteps to take
+	MainFrameTime advance(float p_frame_slice, int p_iterations_per_second);
+};
+
+#endif // TIMER_SYNC_H