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A basic game loop using std::chrono
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/* | |
* 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(¤t_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); | |
} | |
} |
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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Could you explain what errors you're thinking of?