PaceMaker.h

#pragma once
#include <chrono>
#include <thread>
 
class PaceMaker {
    using sys_clock = std::chrono::system_clock;
    sys_clock::time_point frame_begin;
    std::chrono::nanoseconds myNextWait;
    std::chrono::nanoseconds myTargetFrameLen;
    bool initDone = false;
    int fps;
    
public: 
 
    PaceMaker(int _fps)
    {       
        setFps(_fps);
    }
 
    void setFps(int _fps)
    {
        if(_fps <= 0)
        {
            myTargetFrameLen = std::chrono::nanoseconds(1);
        }
        else 
        {
            myTargetFrameLen = std::chrono::nanoseconds(1000000000 / _fps);
        }
        fps = _fps;
    }
 
    void start() {
        if (!initDone)
        {
            myNextWait = myTargetFrameLen;
            frame_begin = sys_clock::now();
            initDone = true;
        }
    }
 
    void end() {
        
        std::chrono::nanoseconds frame_len = sys_clock::now() - frame_begin;
        if (myNextWait > frame_len)
        {
            std::this_thread::sleep_for(myNextWait - frame_len);
        }
        myNextWait += myTargetFrameLen;
    }
 
};