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/* FrameTimer.h
Copyright (c) 2014 by Michael Zahniser
Endless Sky is free software: you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any later version.
Endless Sky is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program. If not, see <https://www.gnu.org/licenses/>.
*/
#pragma once
#include <chrono>
// Class to be used for enforcing a certain frame rate. This ensures that the
// frames are not drawn faster than a certain speed, but if the calculations or
// the graphics cannot keep up it will allow things to go slower for a few frames
// without trying to "catch up" by making the subsequent frame faster.
class FrameTimer {
public:
// Create a timer that is just responsible for measuring the time that
// elapses until Time() is called.
FrameTimer();
// Create a frame timer that will space frames out at exactly the given FPS,
// _unless_ a frame takes too long by at least the given lag, in which case
// the next frame happens immediately but no "catch-up" is done.
explicit FrameTimer(int fps, int maxLagMsec = 5);
// Wait until the next frame should begin.
void Wait();
// Find out how long it has been since this timer was created, in seconds.
double Time() const;
// Change the frame rate (for viewing in slow motion).
void SetFrameRate(int fps);
private:
// Calculate when the next frame should begin.
void Step();
private:
std::chrono::steady_clock::time_point next;
std::chrono::steady_clock::duration step;
std::chrono::steady_clock::duration maxLag;
};
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