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/*************************************************************************/
/* timer_sync.cpp */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2018 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2018 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 "timer_sync.h"
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;
}
}
/////////////////////////////////
// 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);
if (current_min > p_max)
return i; // bail out of further restrictions would void the interval
else if (current_min > p_min)
p_min = current_min;
const float 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_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;
// 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;
}
// 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;
}
}
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) {
if (fixed_fps != -1)
p_idle_step = 1.0 / fixed_fps;
// 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);
// restore time_accum
time_accum = ret.idle_step - idle_minus_accum;
// track deficit
time_deficit = p_idle_step - ret.idle_step;
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;
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);
}
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