228 lines
8.9 KiB
C++
228 lines
8.9 KiB
C++
/*************************************************************************/
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/* main_timer_sync.cpp */
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/*************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/*************************************************************************/
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/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur. */
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/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md). */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/*************************************************************************/
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#include "main_timer_sync.h"
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void MainFrameTime::clamp_idle(float min_idle_step, float max_idle_step) {
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if (idle_step < min_idle_step) {
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idle_step = min_idle_step;
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} else if (idle_step > max_idle_step) {
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idle_step = max_idle_step;
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}
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}
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/////////////////////////////////
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// returns the fraction of p_frame_slice required for the timer to overshoot
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// before advance_core considers changing the physics_steps return from
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// the typical values as defined by typical_physics_steps
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float MainTimerSync::get_physics_jitter_fix() {
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return Engine::get_singleton()->get_physics_jitter_fix();
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}
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// gets our best bet for the average number of physics steps per render frame
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// return value: number of frames back this data is consistent
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int MainTimerSync::get_average_physics_steps(float &p_min, float &p_max) {
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p_min = typical_physics_steps[0];
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p_max = p_min + 1;
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for (int i = 1; i < CONTROL_STEPS; ++i) {
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const float typical_lower = typical_physics_steps[i];
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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 of 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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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;
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}
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// advance physics clock by p_idle_step, return appropriate number of steps to simulate
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MainFrameTime MainTimerSync::advance_core(float p_frame_slice, int p_iterations_per_second, float p_idle_step) {
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MainFrameTime ret;
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ret.idle_step = p_idle_step;
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// simple determination of number of physics iteration
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time_accum += ret.idle_step;
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ret.physics_steps = floor(time_accum * p_iterations_per_second);
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int min_typical_steps = typical_physics_steps[0];
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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
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bool update_typical = false;
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for (int i = 0; i < CONTROL_STEPS - 1; ++i) {
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int steps_left_to_match_typical = typical_physics_steps[i + 1] - accumulated_physics_steps[i];
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if (steps_left_to_match_typical > max_typical_steps ||
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steps_left_to_match_typical + 1 < min_typical_steps) {
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update_typical = true;
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break;
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}
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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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// try to keep it consistent with previous iterations
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if (ret.physics_steps < min_typical_steps) {
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const int max_possible_steps = floor((time_accum)*p_iterations_per_second + get_physics_jitter_fix());
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if (max_possible_steps < min_typical_steps) {
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ret.physics_steps = max_possible_steps;
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update_typical = true;
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} else {
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ret.physics_steps = min_typical_steps;
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}
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} else if (ret.physics_steps > max_typical_steps) {
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const int min_possible_steps = floor((time_accum)*p_iterations_per_second - get_physics_jitter_fix());
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if (min_possible_steps > max_typical_steps) {
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ret.physics_steps = min_possible_steps;
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update_typical = true;
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} else {
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ret.physics_steps = max_typical_steps;
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}
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}
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time_accum -= ret.physics_steps * p_frame_slice;
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// keep track of accumulated step counts
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for (int i = CONTROL_STEPS - 2; i >= 0; --i) {
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accumulated_physics_steps[i + 1] = accumulated_physics_steps[i] + ret.physics_steps;
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}
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accumulated_physics_steps[0] = ret.physics_steps;
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if (update_typical) {
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for (int i = CONTROL_STEPS - 1; i >= 0; --i) {
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if (typical_physics_steps[i] > accumulated_physics_steps[i]) {
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typical_physics_steps[i] = accumulated_physics_steps[i];
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} else if (typical_physics_steps[i] < accumulated_physics_steps[i] - 1) {
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typical_physics_steps[i] = accumulated_physics_steps[i] - 1;
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}
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}
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}
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return ret;
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}
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// calls advance_core, keeps track of deficit it adds to animaption_step, make sure the deficit sum stays close to zero
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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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// compensate for last deficit
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p_idle_step += time_deficit;
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MainFrameTime ret = advance_core(p_frame_slice, p_iterations_per_second, p_idle_step);
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// we will do some clamping on ret.idle_step and need to sync those changes to time_accum,
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// that's easiest if we just remember their fixed difference now
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const double idle_minus_accum = ret.idle_step - time_accum;
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// first, least important clamping: keep ret.idle_step consistent with typical_physics_steps.
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// this smoothes out the idle steps and culls small but quick variations.
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{
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float min_average_physics_steps, max_average_physics_steps;
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int consistent_steps = get_average_physics_steps(min_average_physics_steps, max_average_physics_steps);
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if (consistent_steps > 3) {
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ret.clamp_idle(min_average_physics_steps * p_frame_slice, max_average_physics_steps * p_frame_slice);
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}
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}
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// second clamping: keep abs(time_deficit) < jitter_fix * frame_slise
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float max_clock_deviation = get_physics_jitter_fix() * p_frame_slice;
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ret.clamp_idle(p_idle_step - max_clock_deviation, p_idle_step + max_clock_deviation);
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// last clamping: make sure time_accum is between 0 and p_frame_slice for consistency between physics and idle
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ret.clamp_idle(idle_minus_accum, idle_minus_accum + p_frame_slice);
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// restore time_accum
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time_accum = ret.idle_step - idle_minus_accum;
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// track deficit
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time_deficit = p_idle_step - ret.idle_step;
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// p_frame_slice is 1.0 / iterations_per_sec
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// i.e. the time in seconds taken by a physics tick
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ret.interpolation_fraction = time_accum / p_frame_slice;
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return ret;
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}
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// determine wall clock step since last iteration
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float MainTimerSync::get_cpu_idle_step() {
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uint64_t cpu_ticks_elapsed = current_cpu_ticks_usec - last_cpu_ticks_usec;
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last_cpu_ticks_usec = current_cpu_ticks_usec;
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return cpu_ticks_elapsed / 1000000.0;
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}
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MainTimerSync::MainTimerSync() :
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last_cpu_ticks_usec(0),
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current_cpu_ticks_usec(0),
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time_accum(0),
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time_deficit(0),
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fixed_fps(0) {
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for (int i = CONTROL_STEPS - 1; i >= 0; --i) {
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typical_physics_steps[i] = i;
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accumulated_physics_steps[i] = i;
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}
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}
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// start the clock
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void MainTimerSync::init(uint64_t p_cpu_ticks_usec) {
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current_cpu_ticks_usec = last_cpu_ticks_usec = p_cpu_ticks_usec;
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}
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// set measured wall clock time
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void MainTimerSync::set_cpu_ticks_usec(uint64_t p_cpu_ticks_usec) {
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current_cpu_ticks_usec = p_cpu_ticks_usec;
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}
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void MainTimerSync::set_fixed_fps(int p_fixed_fps) {
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fixed_fps = p_fixed_fps;
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}
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// advance one frame, return timesteps to take
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MainFrameTime MainTimerSync::advance(float p_frame_slice, int p_iterations_per_second) {
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float cpu_idle_step = get_cpu_idle_step();
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return advance_checked(p_frame_slice, p_iterations_per_second, cpu_idle_step);
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}
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