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- /*
- * Copyright (C) 2021 Christopher J. Howard
- *
- * This file is part of Antkeeper source code.
- *
- * Antkeeper source code 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.
- *
- * Antkeeper source code 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 Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
- */
-
- #ifndef ANTKEEPER_FRAME_SCHEDULER_HPP
- #define ANTKEEPER_FRAME_SCHEDULER_HPP
-
- #include <chrono>
- #include <functional>
-
- /**
- * Schedules fixed-timestep update calls and variable timestep render calls.
- *
- * @see https://gafferongames.com/post/fix_your_timestep/
- */
- class frame_scheduler
- {
- public:
- frame_scheduler();
-
- /**
- * Sets the update callback.
- *
- * @param callback Function which takes two parameters: `t`, the total elapsed time, and `dt`, delta time (timestep) which is calculated as `1.0 / update_rate`. This function will be called at the frequency specified by `frame_scheduler::set_update_rate()`.
- */
- void set_update_callback(std::function<void(double, double)> callback);
-
- /**
- * Sets the render callback.
- *
- * @param callback Function which takes one parameter: `alpha`, which is a factor that can be used to interpolate between the previous and current update states.
- */
- void set_render_callback(std::function<void(double)> callback);
-
- /**
- * Sets the update rate.
- *
- * @param frequency Frequency, in hertz, at which the update callback should be called.
- */
- void set_update_rate(double frequency);
-
- /**
- * Sets the maximum duration of a frame. This limits the number of times the update callback is called per frame, thereby preventing a "spiral of death", in which the update callback is called too many times per frame while trying to catch up to the target update rate.
- *
- * @param duration Maximum frame duration, in seconds..
- */
- void set_max_frame_duration(double duration);
-
- /**
- * Returns the duration of the last frame, in seconds.
- */
- double get_frame_duration() const;
-
- /**
- * Resets the total elapsed time, frame duration, and internal timers.
- */
- void reset();
-
- /**
- * Updates the internal timers and performs the scheduled update and render callbacks.
- */
- void tick();
-
- private:
- std::function<void(double, double)> update_callback;
- std::function<void(double)> render_callback;
- double update_rate;
- double update_timestep;
- double max_frame_duration;
- double elapsed_time;
- double accumulator;
- std::chrono::high_resolution_clock::time_point frame_start;
- std::chrono::high_resolution_clock::time_point frame_end;
- double frame_duration;
- };
-
- #endif // ANTKEEPER_FRAME_SCHEDULER_HPP
-
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