How to limit FPS in a loop with C++?

Question

I\'m trying to limit the frames per second in a loop that is performing intersection checking, using C++ with chrono and thread.

Here is my code:

std::ch         


        

Answer 1

This is much like Galik's answer, but it keeps the syntax of the OP's question and doesn't drop down to the C API. Additionally it creates a custom unit for the frame duration which I believe is important for readability:

#include 
#include 
#include 
#include 

int
main()
{
    using namespace std;
    using namespace std::chrono;

    using frames = duration>;  // 5Hz
    auto nextFrame = system_clock::now();
    auto lastFrame = nextFrame - frames{1};;

    while (true)
    {
        // Perform intersection test

        this_thread::sleep_until(nextFrame);
        cout << "Time: "  // just for monitoring purposes
             << duration_cast(system_clock::now() - lastFrame).count()
             << "ms\n";
        lastFrame = nextFrame;
        nextFrame += frames{1};
    }
}

This outputs for me:

Time: 200ms
Time: 205ms
Time: 205ms
Time: 203ms
Time: 205ms
Time: 205ms
Time: 200ms
Time: 200ms
Time: 200ms
...

Key things to note:

• A concise way to document 5Hz: using frames = duration>;
• Use of sleep_until instead of sleep_for, which takes care of the unknown of how long it takes to get the real work done.
• No use of .count() except for I/O, and here's a library to get rid of that.
• No manual conversion of units (e.g. / 1000).
• No floating point units, not that there's anything wrong with that.
• Minimal need to specify or depend upon explicit units.

With the addition of the duration I/O library, here is how the above code would be changed:

#include "chrono_io.h"
#include 
#include 
#include 
#include 

int
main()
{
    using namespace date;
    using namespace std;
    using namespace std::chrono;

    using frames = duration>;  // 5Hz
    auto nextFrame = system_clock::now();
    auto lastFrame = nextFrame - frames{1};;

    while (true)
    {
        // Perform intersection test

        this_thread::sleep_until(nextFrame);
        // just for monitoring purposes
        cout << "Time: " << system_clock::now() - lastFrame << '\n';
        lastFrame = nextFrame;
        nextFrame += frames{1};
    }
}

The output would differ depending upon platform (depending upon the "native duration" of system_clock). On my platform it looks like this:

Time: 200042µs
Time: 205105µs
Time: 205107µs
Time: 200044µs
Time: 205105µs
Time: 200120µs
Time: 204307µs
Time: 205136µs
Time: 201978µs
...