1 files changed, 223 insertions, 0 deletions
diff --git a/main/main_timer_sync.cpp b/main/main_timer_sync.cpp
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+++ b/main/main_timer_sync.cpp
@@ -0,0 +1,223 @@
+/*************************************************************************/
+/*  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;
+
+	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);
+}