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/*************************************************************************/
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/* main_timer_sync.cpp */
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/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
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/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md). */
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# include "main_timer_sync.h"
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# include "core/math/math_funcs.h"
# include "core/os/os.h"
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void MainFrameTime : : clamp_idle ( float min_idle_step , float max_idle_step ) {
if ( idle_step < min_idle_step ) {
idle_step = min_idle_step ;
} else if ( idle_step > max_idle_step ) {
idle_step = max_idle_step ;
}
}
/////////////////////////////////
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void MainTimerSync : : DeltaSmoother : : update_refresh_rate_estimator ( int64_t p_delta ) {
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// the calling code should prevent 0 or negative values of delta
// (preventing divide by zero)
// note that if the estimate gets locked, and something external changes this
// (e.g. user changes to non-vsync in the OS), then the results may be less than ideal,
// but usually it will detect this via the FPS measurement and not attempt smoothing.
// This should be a rare occurrence anyway, and will be cured next time user restarts game.
if ( _ estimate_locked ) {
return ;
}
// First average the delta over NUM_READINGS
_estimator_total_delta + = p_delta ;
_estimator_delta_readings + + ;
const int NUM_READINGS = 60 ;
if ( _estimator_delta_readings < NUM_READINGS ) {
return ;
}
// use average
p_delta = _estimator_total_delta / NUM_READINGS ;
// reset the averager for next time
_estimator_delta_readings = 0 ;
_estimator_total_delta = 0 ;
///////////////////////////////
int fps = Math : : round ( 1000000.0 / p_delta ) ;
// initial estimation, to speed up converging, special case we will estimate the refresh rate
// from the first average FPS reading
if ( _estimated_fps = = 0 ) {
// below 50 might be chugging loading stuff, or else
// dropping loads of frames, so the estimate will be inaccurate
if ( fps > = 50 ) {
_estimated_fps = fps ;
# ifdef GODOT_DEBUG_DELTA_SMOOTHER
print_line ( " initial guess (average measured) refresh rate: " + itos ( fps ) ) ;
# endif
} else {
// can't get started until above 50
return ;
}
}
// we hit our exact estimated refresh rate.
// increase our confidence in the estimate.
if ( fps = = _estimated_fps ) {
// note that each hit is an average of NUM_READINGS frames
_hits_at_estimated + + ;
if ( _estimate_complete & & _hits_at_estimated = = 20 ) {
_estimate_locked = true ;
# ifdef GODOT_DEBUG_DELTA_SMOOTHER
print_line ( " estimate LOCKED at " + itos ( _estimated_fps ) + " fps " ) ;
# endif
return ;
}
// if we are getting pretty confident in this estimate, decide it is complete
// (it can still be increased later, and possibly lowered but only for a short time)
if ( ( ! _estimate_complete ) & & ( _hits_at_estimated > 2 ) ) {
// when the estimate is complete we turn on smoothing
if ( _estimated_fps ) {
_estimate_complete = true ;
_vsync_delta = 1000000 / _estimated_fps ;
# ifdef GODOT_DEBUG_DELTA_SMOOTHER
print_line ( " estimate complete. vsync_delta " + itos ( _vsync_delta ) + " , fps " + itos ( _estimated_fps ) ) ;
# endif
}
}
# ifdef GODOT_DEBUG_DELTA_SMOOTHER
if ( ( _hits_at_estimated % ( 400 / NUM_READINGS ) ) = = 0 ) {
String sz = " hits at estimated : " + itos ( _hits_at_estimated ) + " , above : " + itos ( _hits_above_estimated ) + " ( " + itos ( _hits_one_above_estimated ) + " ), below : " + itos ( _hits_below_estimated ) + " ( " + itos ( _hits_one_below_estimated ) + " ) " ;
print_line ( sz ) ;
}
# endif
return ;
}
const int SIGNIFICANCE_UP = 1 ;
const int SIGNIFICANCE_DOWN = 2 ;
// we are not usually interested in slowing the estimate
// but we may have overshot, so make it possible to reduce
if ( fps < _estimated_fps ) {
// micro changes
if ( fps = = ( _estimated_fps - 1 ) ) {
_hits_one_below_estimated + + ;
if ( ( _hits_one_below_estimated > _hits_at_estimated ) & & ( _hits_one_below_estimated > SIGNIFICANCE_DOWN ) ) {
_estimated_fps - - ;
made_new_estimate ( ) ;
}
return ;
} else {
_hits_below_estimated + + ;
// don't allow large lowering if we are established at a refresh rate, as it will probably be dropped frames
bool established = _estimate_complete & & ( _hits_at_estimated > 10 ) ;
// macro changes
// note there is a large barrier to macro lowering. That is because it is more likely to be dropped frames
// than mis-estimation of the refresh rate.
if ( ! established ) {
if ( ( ( _hits_below_estimated / 8 ) > _hits_at_estimated ) & & ( _hits_below_estimated > SIGNIFICANCE_DOWN ) ) {
// decrease the estimate
_estimated_fps - - ;
made_new_estimate ( ) ;
}
}
return ;
}
}
// Changes increasing the estimate.
// micro changes
if ( fps = = ( _estimated_fps + 1 ) ) {
_hits_one_above_estimated + + ;
if ( ( _hits_one_above_estimated > _hits_at_estimated ) & & ( _hits_one_above_estimated > SIGNIFICANCE_UP ) ) {
_estimated_fps + + ;
made_new_estimate ( ) ;
}
return ;
} else {
_hits_above_estimated + + ;
// macro changes
if ( ( _hits_above_estimated > _hits_at_estimated ) & & ( _hits_above_estimated > SIGNIFICANCE_UP ) ) {
// increase the estimate
int change = fps - _estimated_fps ;
change / = 2 ;
change = MAX ( 1 , change ) ;
_estimated_fps + = change ;
made_new_estimate ( ) ;
}
return ;
}
}
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bool MainTimerSync : : DeltaSmoother : : fps_allows_smoothing ( int64_t p_delta ) {
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_measurement_time + = p_delta ;
_measurement_frame_count + + ;
if ( _measurement_frame_count = = _measurement_end_frame ) {
// only switch on or off if the estimate is complete
if ( _estimate_complete ) {
int64_t time_passed = _measurement_time - _measurement_start_time ;
// average delta
time_passed / = MEASURE_FPS_OVER_NUM_FRAMES ;
// estimate fps
if ( time_passed ) {
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double fps = 1000000.0 / time_passed ;
double ratio = fps / ( double ) _estimated_fps ;
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//print_line("ratio : " + String(Variant(ratio)));
if ( ( ratio > 0.95 ) & & ( ratio < 1.05 ) ) {
_measurement_allows_smoothing = true ;
} else {
_measurement_allows_smoothing = false ;
}
}
} // estimate complete
// new start time for next iteration
_measurement_start_time = _measurement_time ;
_measurement_end_frame + = MEASURE_FPS_OVER_NUM_FRAMES ;
}
return _measurement_allows_smoothing ;
}
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int64_t MainTimerSync : : DeltaSmoother : : smooth_delta ( int64_t p_delta ) {
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// Conditions to disable smoothing.
// Note that vsync is a request, it cannot be relied on, the OS may override this.
// If the OS turns vsync on without vsync in the app, smoothing will not be enabled.
// If the OS turns vsync off with sync enabled in the app, the smoothing must detect this
// via the error metric and switch off.
if ( ! OS : : get_singleton ( ) - > is_delta_smoothing_enabled ( ) | | ! OS : : get_singleton ( ) - > is_vsync_enabled ( ) | | Engine : : get_singleton ( ) - > is_editor_hint ( ) ) {
return p_delta ;
}
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// Very important, ignore long deltas and pass them back unmodified.
// This is to deal with resuming after suspend for long periods.
if ( p_delta > 1000000 ) {
return p_delta ;
}
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// keep a running guesstimate of the FPS, and turn off smoothing if
// conditions not close to the estimated FPS
if ( ! fps_allows_smoothing ( p_delta ) ) {
return p_delta ;
}
// we can't cope with negative deltas .. OS bug on some hardware
// and also very small deltas caused by vsync being off.
// This could possibly be part of a hiccup, this value isn't fixed in stone...
if ( p_delta < 1000 ) {
return p_delta ;
}
// note still some vsync off will still get through to this point...
// and we need to cope with it by not converging the estimator / and / or not smoothing
update_refresh_rate_estimator ( p_delta ) ;
// no smoothing until we know what the refresh rate is
if ( ! _estimate_complete ) {
return p_delta ;
}
// accumulate the time we have available to use
_leftover_time + = p_delta ;
// how many vsyncs units can we fit?
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int64_t units = _leftover_time / _vsync_delta ;
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// a delta must include minimum 1 vsync
// (if it is less than that, it is either random error or we are no longer running at the vsync rate,
// in which case we should switch off delta smoothing, or re-estimate the refresh rate)
units = MAX ( units , 1 ) ;
_leftover_time - = units * _vsync_delta ;
// print_line("units " + itos(units) + ", leftover " + itos(_leftover_time/1000) + " ms");
return units * _vsync_delta ;
}
/////////////////////////////////////
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// 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 MainTimerSync : : get_physics_jitter_fix ( ) {
return Engine : : get_singleton ( ) - > 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 MainTimerSync : : get_average_physics_steps ( float & p_min , float & p_max ) {
p_min = typical_physics_steps [ 0 ] ;
p_max = p_min + 1 ;
for ( int i = 1 ; i < CONTROL_STEPS ; + + i ) {
const float typical_lower = typical_physics_steps [ i ] ;
const float current_min = typical_lower / ( i + 1 ) ;
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if ( current_min > p_max ) {
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return i ; // bail out if further restrictions would void the interval
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} else if ( current_min > p_min ) {
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p_min = current_min ;
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}
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const float current_max = ( typical_lower + 1 ) / ( i + 1 ) ;
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if ( current_max < p_min ) {
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return i ;
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} else if ( current_max < p_max ) {
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p_max = current_max ;
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}
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}
return CONTROL_STEPS ;
}
// advance physics clock by p_idle_step, return appropriate number of steps to simulate
MainFrameTime MainTimerSync : : advance_core ( float p_frame_slice , int p_iterations_per_second , float p_idle_step ) {
MainFrameTime ret ;
ret . idle_step = p_idle_step ;
// simple determination of number of physics iteration
time_accum + = ret . idle_step ;
ret . physics_steps = floor ( time_accum * p_iterations_per_second ) ;
int min_typical_steps = typical_physics_steps [ 0 ] ;
int max_typical_steps = min_typical_steps + 1 ;
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// given the past recorded steps and typical steps to match, calculate bounds for this
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// step to be typical
bool update_typical = false ;
for ( int i = 0 ; i < CONTROL_STEPS - 1 ; + + i ) {
int steps_left_to_match_typical = typical_physics_steps [ i + 1 ] - accumulated_physics_steps [ i ] ;
if ( steps_left_to_match_typical > max_typical_steps | |
steps_left_to_match_typical + 1 < min_typical_steps ) {
update_typical = true ;
break ;
}
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if ( steps_left_to_match_typical > min_typical_steps ) {
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min_typical_steps = steps_left_to_match_typical ;
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}
if ( steps_left_to_match_typical + 1 < max_typical_steps ) {
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max_typical_steps = steps_left_to_match_typical + 1 ;
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}
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}
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# ifdef DEBUG_ENABLED
if ( max_typical_steps < 0 ) {
WARN_PRINT_ONCE ( " `max_typical_steps` is negative. This could hint at an engine bug or system timer misconfiguration. " ) ;
}
# endif
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// try to keep it consistent with previous iterations
if ( ret . physics_steps < min_typical_steps ) {
const int max_possible_steps = floor ( ( time_accum ) * p_iterations_per_second + get_physics_jitter_fix ( ) ) ;
if ( max_possible_steps < min_typical_steps ) {
ret . physics_steps = max_possible_steps ;
update_typical = true ;
} else {
ret . physics_steps = min_typical_steps ;
}
} else if ( ret . physics_steps > max_typical_steps ) {
const int min_possible_steps = floor ( ( time_accum ) * p_iterations_per_second - get_physics_jitter_fix ( ) ) ;
if ( min_possible_steps > max_typical_steps ) {
ret . physics_steps = min_possible_steps ;
update_typical = true ;
} else {
ret . physics_steps = max_typical_steps ;
}
}
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if ( ret . physics_steps < 0 ) {
ret . physics_steps = 0 ;
}
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time_accum - = ret . physics_steps * p_frame_slice ;
// keep track of accumulated step counts
for ( int i = CONTROL_STEPS - 2 ; i > = 0 ; - - i ) {
accumulated_physics_steps [ i + 1 ] = accumulated_physics_steps [ i ] + ret . physics_steps ;
}
accumulated_physics_steps [ 0 ] = ret . physics_steps ;
if ( update_typical ) {
for ( int i = CONTROL_STEPS - 1 ; i > = 0 ; - - i ) {
if ( typical_physics_steps [ i ] > accumulated_physics_steps [ i ] ) {
typical_physics_steps [ i ] = accumulated_physics_steps [ i ] ;
} else if ( typical_physics_steps [ i ] < accumulated_physics_steps [ i ] - 1 ) {
typical_physics_steps [ i ] = accumulated_physics_steps [ i ] - 1 ;
}
}
}
return ret ;
}
// calls advance_core, keeps track of deficit it adds to animaption_step, make sure the deficit sum stays close to zero
MainFrameTime MainTimerSync : : advance_checked ( float p_frame_slice , int p_iterations_per_second , float p_idle_step ) {
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if ( fixed_fps ! = - 1 ) {
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p_idle_step = 1.0 / fixed_fps ;
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}
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float min_output_step = p_idle_step / 8 ;
min_output_step = MAX ( min_output_step , 1E-6 ) ;
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// compensate for last deficit
p_idle_step + = time_deficit ;
MainFrameTime ret = advance_core ( p_frame_slice , p_iterations_per_second , p_idle_step ) ;
// we will do some clamping on ret.idle_step and need to sync those changes to time_accum,
// that's easiest if we just remember their fixed difference now
const double idle_minus_accum = ret . idle_step - time_accum ;
// first, least important clamping: keep ret.idle_step consistent with typical_physics_steps.
// this smoothes out the idle steps and culls small but quick variations.
{
float min_average_physics_steps , max_average_physics_steps ;
int consistent_steps = get_average_physics_steps ( min_average_physics_steps , max_average_physics_steps ) ;
if ( consistent_steps > 3 ) {
ret . clamp_idle ( min_average_physics_steps * p_frame_slice , max_average_physics_steps * p_frame_slice ) ;
}
}
// second clamping: keep abs(time_deficit) < jitter_fix * frame_slise
float max_clock_deviation = get_physics_jitter_fix ( ) * p_frame_slice ;
ret . clamp_idle ( p_idle_step - max_clock_deviation , p_idle_step + max_clock_deviation ) ;
// last clamping: make sure time_accum is between 0 and p_frame_slice for consistency between physics and idle
ret . clamp_idle ( idle_minus_accum , idle_minus_accum + p_frame_slice ) ;
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// all the operations above may have turned ret.idle_step negative or zero, keep a minimal value
if ( ret . idle_step < min_output_step ) {
ret . idle_step = min_output_step ;
}
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// restore time_accum
time_accum = ret . idle_step - idle_minus_accum ;
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// forcing ret.idle_step to be positive may trigger a violation of the
// promise that time_accum is between 0 and p_frame_slice
# ifdef DEBUG_ENABLED
if ( time_accum < - 1E-7 ) {
WARN_PRINT_ONCE ( " Intermediate value of `time_accum` is negative. This could hint at an engine bug or system timer misconfiguration. " ) ;
}
# endif
if ( time_accum > p_frame_slice ) {
const int extra_physics_steps = floor ( time_accum * p_iterations_per_second ) ;
time_accum - = extra_physics_steps * p_frame_slice ;
ret . physics_steps + = extra_physics_steps ;
}
# ifdef DEBUG_ENABLED
if ( time_accum < - 1E-7 ) {
WARN_PRINT_ONCE ( " Final value of `time_accum` is negative. It should always be between 0 and `p_physics_step`. This hints at an engine bug. " ) ;
}
if ( time_accum > p_frame_slice + 1E-7 ) {
WARN_PRINT_ONCE ( " Final value of `time_accum` is larger than `p_frame_slice`. It should always be between 0 and `p_frame_slice`. This hints at an engine bug. " ) ;
}
# endif
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// track deficit
time_deficit = p_idle_step - ret . idle_step ;
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// p_frame_slice is 1.0 / iterations_per_sec
// i.e. the time in seconds taken by a physics tick
ret . interpolation_fraction = time_accum / p_frame_slice ;
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return ret ;
}
// determine wall clock step since last iteration
float MainTimerSync : : get_cpu_idle_step ( ) {
uint64_t cpu_ticks_elapsed = current_cpu_ticks_usec - last_cpu_ticks_usec ;
last_cpu_ticks_usec = current_cpu_ticks_usec ;
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cpu_ticks_elapsed = _delta_smoother . smooth_delta ( cpu_ticks_elapsed ) ;
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return cpu_ticks_elapsed / 1000000.0 ;
}
MainTimerSync : : MainTimerSync ( ) :
last_cpu_ticks_usec ( 0 ) ,
current_cpu_ticks_usec ( 0 ) ,
time_accum ( 0 ) ,
time_deficit ( 0 ) ,
fixed_fps ( 0 ) {
for ( int i = CONTROL_STEPS - 1 ; i > = 0 ; - - i ) {
typical_physics_steps [ i ] = i ;
accumulated_physics_steps [ i ] = i ;
}
}
// start the clock
void MainTimerSync : : init ( uint64_t p_cpu_ticks_usec ) {
current_cpu_ticks_usec = last_cpu_ticks_usec = p_cpu_ticks_usec ;
}
// set measured wall clock time
void MainTimerSync : : set_cpu_ticks_usec ( uint64_t p_cpu_ticks_usec ) {
current_cpu_ticks_usec = p_cpu_ticks_usec ;
}
void MainTimerSync : : set_fixed_fps ( int p_fixed_fps ) {
fixed_fps = p_fixed_fps ;
}
// advance one frame, return timesteps to take
MainFrameTime MainTimerSync : : advance ( float p_frame_slice , int p_iterations_per_second ) {
float cpu_idle_step = get_cpu_idle_step ( ) ;
return advance_checked ( p_frame_slice , p_iterations_per_second , cpu_idle_step ) ;
}