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/*************************************************************************/
/* main_timer_sync.cpp */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md). */
/* */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the */
/* "Software"), to deal in the Software without restriction, including */
/* without limitation the rights to use, copy, modify, merge, publish, */
/* distribute, sublicense, and/or sell copies of the Software, and to */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions: */
/* */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/*************************************************************************/
#include "main_timer_sync.h"
void MainFrameTime::clamp_process_step(double min_process_step, double max_process_step) {
if (process_step < min_process_step) {
process_step = min_process_step;
} else if (process_step > max_process_step) {
process_step = max_process_step;
}
}
/////////////////////////////////
// returns the fraction of p_physics_step 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
double 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(double &p_min, double &p_max) {
p_min = typical_physics_steps[0];
p_max = p_min + 1;
for (int i = 1; i < CONTROL_STEPS; ++i) {
const double typical_lower = typical_physics_steps[i];
const double current_min = typical_lower / (i + 1);
if (current_min > p_max) {
return i; // bail out if further restrictions would void the interval
} else if (current_min > p_min) {
p_min = current_min;
}
const double current_max = (typical_lower + 1) / (i + 1);
if (current_max < p_min) {
return i;
} else if (current_max < p_max) {
p_max = current_max;
}
}
return CONTROL_STEPS;
}
// advance physics clock by p_process_step, return appropriate number of steps to simulate
MainFrameTime MainTimerSync::advance_core(double p_physics_step, int p_physics_ticks_per_second, double p_process_step) {
MainFrameTime ret;
ret.process_step = p_process_step;
// simple determination of number of physics iteration
time_accum += ret.process_step;
ret.physics_steps = floor(time_accum * p_physics_ticks_per_second);
int min_typical_steps = typical_physics_steps[0];
int max_typical_steps = min_typical_steps + 1;
// given the past recorded steps and typical steps to match, calculate bounds for this
// 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;
}
if (steps_left_to_match_typical > min_typical_steps) {
min_typical_steps = steps_left_to_match_typical;
}
if (steps_left_to_match_typical + 1 < max_typical_steps) {
max_typical_steps = steps_left_to_match_typical + 1;
}
}
#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
// try to keep it consistent with previous iterations
if (ret.physics_steps < min_typical_steps) {
const int max_possible_steps = floor((time_accum)*p_physics_ticks_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_physics_ticks_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;
}
}
if (ret.physics_steps < 0) {
ret.physics_steps = 0;
}
time_accum -= ret.physics_steps * p_physics_step;
// 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(double p_physics_step, int p_physics_ticks_per_second, double p_process_step) {
if (fixed_fps != -1) {
p_process_step = 1.0 / fixed_fps;
}
float min_output_step = p_process_step / 8;
min_output_step = MAX(min_output_step, 1E-6);
// compensate for last deficit
p_process_step += time_deficit;
MainFrameTime ret = advance_core(p_physics_step, p_physics_ticks_per_second, p_process_step);
// we will do some clamping on ret.process_step and need to sync those changes to time_accum,
// that's easiest if we just remember their fixed difference now
const double process_minus_accum = ret.process_step - time_accum;
// first, least important clamping: keep ret.process_step consistent with typical_physics_steps.
// this smoothes out the process steps and culls small but quick variations.
{
double 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_process_step(min_average_physics_steps * p_physics_step, max_average_physics_steps * p_physics_step);
}
}
// second clamping: keep abs(time_deficit) < jitter_fix * frame_slise
double max_clock_deviation = get_physics_jitter_fix() * p_physics_step;
ret.clamp_process_step(p_process_step - max_clock_deviation, p_process_step + max_clock_deviation);
// last clamping: make sure time_accum is between 0 and p_physics_step for consistency between physics and process
ret.clamp_process_step(process_minus_accum, process_minus_accum + p_physics_step);
// all the operations above may have turned ret.p_process_step negative or zero, keep a minimal value
if (ret.process_step < min_output_step) {
ret.process_step = min_output_step;
}
// restore time_accum
time_accum = ret.process_step - process_minus_accum;
// forcing ret.process_step to be positive may trigger a violation of the
// promise that time_accum is between 0 and p_physics_step
#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_physics_step) {
const int extra_physics_steps = floor(time_accum * p_physics_ticks_per_second);
time_accum -= extra_physics_steps * p_physics_step;
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_physics_step + 1E-7) {
WARN_PRINT_ONCE("Final value of `time_accum` is larger than `p_physics_step`. It should always be between 0 and `p_physics_step`. This hints at an engine bug.");
}
#endif
// track deficit
time_deficit = p_process_step - ret.process_step;
// p_physics_step is 1.0 / iterations_per_sec
// i.e. the time in seconds taken by a physics tick
ret.interpolation_fraction = time_accum / p_physics_step;
return ret;
}
// determine wall clock step since last iteration
double MainTimerSync::get_cpu_process_step() {
uint64_t cpu_ticks_elapsed = current_cpu_ticks_usec - last_cpu_ticks_usec;
last_cpu_ticks_usec = current_cpu_ticks_usec;
return cpu_ticks_elapsed / 1000000.0;
}
MainTimerSync::MainTimerSync() {
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 physics frame, return timesteps to take
MainFrameTime MainTimerSync::advance(double p_physics_step, int p_physics_ticks_per_second) {
double cpu_process_step = get_cpu_process_step();
return advance_checked(p_physics_step, p_physics_ticks_per_second, cpu_process_step);
}
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