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

If you think about how your code works, you'll find out that it works exactly how you wrote it. Delta oscillates because of a logical mistake in the code.

This is what happens:

• We start with delta == 0.
• Because the delta is smaller than 200, you code sleeps 200 - delta(0) == 200 ms.
• Now, the delta itself becomes close to 200 (because you've measured that sleep time as well as an actual work) and you sleep 200 - delta(200) == 0 ms.
• After that the cycle repeats.

To fix the problem you need to not measure the sleep time.

This is how it can be done:

#include 
#include 
#include 
#include 

std::chrono::system_clock::time_point a = std::chrono::system_clock::now();
std::chrono::system_clock::time_point b = std::chrono::system_clock::now();

int main()
{
    while (true)
    {
        // Maintain designated frequency of 5 Hz (200 ms per frame)
        a = std::chrono::system_clock::now();
        std::chrono::duration work_time = a - b;

        if (work_time.count() < 200.0)
        {
            std::chrono::duration delta_ms(200.0 - work_time.count());
            auto delta_ms_duration = std::chrono::duration_cast(delta_ms);
            std::this_thread::sleep_for(std::chrono::milliseconds(delta_ms_duration.count()));
        }

        b = std::chrono::system_clock::now();
        std::chrono::duration sleep_time = b - a;

        // Your code here

        printf("Time: %f \n", (work_time + sleep_time).count());
    }
}

This code gives me a steady sequence of deltas:

Time: 199.057206 
Time: 199.053581 
Time: 199.064718 
Time: 199.053515 
Time: 199.053307 
Time: 199.053415 
Time: 199.053164 
Time: 199.053511 
Time: 199.053280 
Time: 199.053283