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Last active May 23, 2024 02:36
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A basic game loop using std::chrono
/*
* The MIT License (MIT)
*
* Copyright (c) 2016 Mario Badr
*
* 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 <chrono>
using namespace std::chrono_literals;
// we use a fixed timestep of 1 / (60 fps) = 16 milliseconds
constexpr std::chrono::nanoseconds timestep(16ms);
struct game_state {
// this contains the state of your game, such as positions and velocities
};
bool handle_events() {
// poll for events
return false; // true if the user wants to quit the game
}
void update(game_state *) {
// update game logic here
}
void render(game_state const &) {
// render stuff here
}
game_state interpolate(game_state const & current, game_state const & previous, float alpha) {
game_state interpolated_state;
// interpolate between previous and current by alpha here
return interpolated_state;
}
int main() {
using clock = std::chrono::high_resolution_clock;
std::chrono::nanoseconds lag(0ns);
auto time_start = clock::now();
bool quit_game = false;
game_state current_state;
game_state previous_state;
while(!quit_game) {
auto delta_time = clock::now() - time_start;
time_start = clock::now();
lag += std::chrono::duration_cast<std::chrono::nanoseconds>(delta_time);
quit_game = handle_events();
// update game logic as lag permits
while(lag >= timestep) {
lag -= timestep;
previous_state = current_state;
update(&current_state); // update at a fixed rate each time
}
// calculate how close or far we are from the next timestep
auto alpha = (float) lag.count() / timestep.count();
auto interpolated_state = interpolate(current_state, previous_state, alpha);
render(interpolated_state);
}
}
@littlelies77
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auto delta_time = clock::now() - time_start;
time_start = clock::now();

This will lead to errors overtime. Instead.

			auto current_time = clock();
			auto frame_time = current_time - base_time;
			base_time = current_time;
			lag += std::chrono::duration_cast<std::chrono::nanoseconds>(frame_time);

@htmlboss
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auto delta_time = clock::now() - time_start;
time_start = clock::now();

This will lead to errors overtime. Instead.

			auto current_time = clock();
			auto frame_time = current_time - base_time;
			base_time = current_time;
			lag += std::chrono::duration_cast<std::chrono::nanoseconds>(frame_time);

Could you explain what errors you're thinking of?

@test544
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test544 commented Sep 25, 2023

Could you explain what errors you're thinking of?

probably nobody care, but nevertheless - the problem is that two consecutive calls, even if they are back-to-back, can(will?) produce the different results. Hence you should call the get() once and cache the result.

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