godot/main/main_timer_sync.cpp
lawnjelly bf6c301b9c Add access to interpolation fraction for fixed timestep interpolation
Addresses #30068

This is a prerequisite for allowing proper support for fixed timestep interpolation, exposing the interpolation fraction to the engine, modules and gdscript.

The interpolation fraction is the fraction through the current physics tick at the time of the current frame.
2019-07-11 08:25:26 +01:00

227 lines
8.9 KiB
C++

/*************************************************************************/
/* main_timer_sync.cpp */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2019 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2019 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_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;
// 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;
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);
}