godot/main/main_timer_sync.h
lawnjelly 6914d7c6e0 Add frame delta smoothing option
Frame deltas are currently measured by querying the OS timer each frame. This is subject to random error. Frame delta smoothing instead filters the delta read from the OS by replacing it with the refresh rate delta wherever possible.

This PR also contains code to estimate the refresh rate based on the input deltas, without reading the refresh rate from the host OS.
2021-07-14 08:44:31 +01:00

166 lines
6.7 KiB
C++

/*************************************************************************/
/* main_timer_sync.h */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md). */
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#ifndef MAIN_TIMER_SYNC_H
#define MAIN_TIMER_SYNC_H
#include "core/engine.h"
// define these to get more debugging logs for the delta smoothing
//#define GODOT_DEBUG_DELTA_SMOOTHER
struct MainFrameTime {
float idle_step; // time to advance idles for (argument to process())
int physics_steps; // number of times to iterate the physics engine
float interpolation_fraction; // fraction through the current physics tick
void clamp_idle(float min_idle_step, float max_idle_step);
};
class MainTimerSync {
class DeltaSmoother {
public:
// pass the recorded delta, returns a smoothed delta
int smooth_delta(int p_delta);
private:
void update_refresh_rate_estimator(int p_delta);
bool fps_allows_smoothing(int p_delta);
// estimated vsync delta (monitor refresh rate)
int64_t _vsync_delta = 16666;
// keep track of accumulated time so we know how many vsyncs to advance by
int64_t _leftover_time = 0;
// keep a rough measurement of the FPS as we run.
// If this drifts a long way below or above the refresh rate, the machine
// is struggling to keep up, and we can switch off smoothing. This
// also deals with the case that the user has overridden the vsync in the GPU settings,
// in which case we don't want to try smoothing.
static const int MEASURE_FPS_OVER_NUM_FRAMES = 64;
int64_t _measurement_time = 0;
int64_t _measurement_frame_count = 0;
int64_t _measurement_end_frame = MEASURE_FPS_OVER_NUM_FRAMES;
int64_t _measurement_start_time = 0;
bool _measurement_allows_smoothing = true;
// we can estimate the fps by growing it on condition
// that a large proportion of frames are higher than the current estimate.
int _estimated_fps = 0;
int _hits_at_estimated = 0;
int _hits_above_estimated = 0;
int _hits_below_estimated = 0;
int _hits_one_above_estimated = 0;
int _hits_one_below_estimated = 0;
bool _estimate_complete = false;
bool _estimate_locked = false;
// data for averaging the delta over a second or so
// to prevent spurious values
int _estimator_total_delta = 0;
int _estimator_delta_readings = 0;
void made_new_estimate() {
_hits_above_estimated = 0;
_hits_at_estimated = 0;
_hits_below_estimated = 0;
_hits_one_above_estimated = 0;
_hits_one_below_estimated = 0;
_estimate_complete = false;
#ifdef GODOT_DEBUG_DELTA_SMOOTHER
print_line("estimated fps " + itos(_estimated_fps));
#endif
}
} _delta_smoother;
// 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 // MAIN_TIMER_SYNC_H