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Window / Frame Rate/Periodic Lag Issues

« on: August 25, 2013, 07:51:57 pm »

Hi everybody,

I'm new to SFML and new to the forum so sorry if I haven't posted correctly, but I'm having some issues with my C++ game.

My problem is that I'm getting inconsistent lag. I have searched around for solutions to frame rate issues and found people telling me to use Vsync, which I did but it didn't improve the situation. I've tried using an if statement inside my while(window.isOpen()) loop with sf::Clock.getTimeElapsed.asSeconds() > 1.0f/30.0f (my desired frame rate), and I've also tried to use the setFramerateLimit(30) function, but none of this seems to help.

The strange thing is, that I have tested the framerate by outputting the elapsed time to the console every frame, and the elapsed time is close to 0.033 for 9 or so frames, then it randomly increases to about 0.08, then back down again, and this cycle repeats, so the spike is about every half second.

Can anyone explain this weird behaviour? I am running this on a powerful machine, and my game has fairly efficient game logic, so I can't explain why these lag spikes occur. I didn't think including source code would be useful, but I can if anyone wants to take a look.
Any help would be greatly appreciated.

Thanks. 


Update:

I'm still at a loss, I've tried it even using basic minimal coding, and i'm still getting lagg spikes

int main()
{
    sf::RenderWindow window(sf::VideoMode(800, 600), "Window");
        window.setVerticalSyncEnabled(true);
        sf::Clock clock;
        float currTime = 0.0f;
        float prevTime = 0.0f;

    while (window.isOpen())
    {
                        sf::Event event;
                        while (window.pollEvent(event))
                        {
                                if (event.type == sf::Event::Closed)
                                        window.close();
                        }
                        currTime = clock.getElapsedTime().asSeconds();
                        std::cout << currTime - prevTime << std::endl;
                        prevTime = currTime;
                        window.clear(sf::Color::Black);
                        window.display();
                        sf::sleep(sf::Time(sf::milliseconds(20)));
    }

    return 0;
}
 

I've got a screenshot of what the console outputs here, showing where the spikes occur:

Any help greatly appreciated