From d5abd4eb750387c95d1040e7613f98bd816c58bb Mon Sep 17 00:00:00 2001 From: Manuel Moos Date: Sun, 11 Feb 2018 00:03:31 +0100 Subject: Add hysteresis to physics timestep count per frame Add new class _TimerSync to manage timestep calculations. The new class handles the decisions about simulation progression previously handled by main::iteration(). It is fed the current timer ticks and determines how many physics updates are to be run and what the delta argument to the _process() functions should be. The new class tries to keep the number of physics updates per frame as constant as possible from frame to frame. Ideally, it would be N steps every render frame, but even with perfectly regular rendering, the general case is that N or N+1 steps are required per frame, for some fixed N. The best guess for N is stored in typical_physics_steps. When determining the number of steps to take, no restrictions are imposed between the choice of typical_physics_steps and typical_physics_steps+1 steps. Should more or less steps than that be required, the accumulated remaining time (as before, stored in time_accum) needs to surpass its boundaries by some minimal threshold. Once surpassed, typical_physics_steps is updated to allow the new step count for future updates. Care is taken that the modified calculation of the number of physics steps is not observable from game code that only checks the delta parameters to the _process and _physics_process functions; in addition to modifying the number of steps, the _process argument is modified as well to stay in expected bounds. Extra care is taken that the accumulated steps still sum up to roughly the real elapsed time, up to a maximum tolerated difference. To allow the hysteresis code to work correctly on higher refresh monitors, the number of typical physics steps is not only recorded and kept consistent for single render frames, but for groups of them. Currently, up to 12 frames are grouped that way. The engine parameter physics_jitter_fix controls both the maximum tolerated difference between wall clock time and summed up _process arguments and the threshold for changing typical_physics_steps. It is given in units of the real physics frame slice 1/physics_fps. Set physics_jitter_fix to 0 to disable the effects of the new code here. It starts to be effective against the random physics jitter at around 0.02 to 0.05. at values greater than 1 it starts having ill effects on the engine's ability to react sensibly to dropped frames and framerate changes. --- core/engine.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'core/engine.h') diff --git a/core/engine.h b/core/engine.h index 54b30ab81f..665992699a 100644 --- a/core/engine.h +++ b/core/engine.h @@ -57,6 +57,7 @@ private: float _frame_step; int ips; + float physics_jitter_fix; float _fps; int _target_fps; float _time_scale; @@ -79,6 +80,9 @@ public: virtual void set_iterations_per_second(int p_ips); virtual int get_iterations_per_second() const; + void set_physics_jitter_fix(float p_threshold); + float get_physics_jitter_fix() const; + virtual void set_target_fps(int p_fps); virtual float get_target_fps() const; -- cgit v1.2.3