I'm currently working on a platformer and trying to implement a timestep, but for framerate limits greater than 60 the CPU usage goes up from 1% to 25% and more.
I made this minimal program to demonstrate the issue. There are two comments (in red, lines 10-13, lines 26-30) in the code that describe the problem and what I have tested.
Note that the FPS stuff is not relevant to the problem (I think).
I tried to keep the code short and simple:
#include <memory>
#include <sstream>
#include <iomanip>
#include <SFML\Graphics.hpp>
int main() {
// Window
std::shared_ptr<sf::RenderWindow> window;
window = std::make_shared<sf::RenderWindow>(sf::VideoMode(640, 480, 32), "Test", sf::Style::Close);
/*
When I use the setFramerateLimit() function below, the CPU usage is only 1% instead of 25%+
(And only if I set the limit to 60 or less. For example 120 increases CPU usage to 25%+ again.)
*/
//window->setFramerateLimit(60);
// FPS text
sf::Font font;
font.loadFromFile("font.ttf");
sf::Text fpsText("", font, 30);
fpsText.setColor(sf::Color(0, 0, 0));
// FPS
float fps;
sf::Clock fpsTimer;
sf::Time fpsElapsedTime;
/*
When I set framerateLimit to 60 (or anything less than 60)
instead of 120, CPU usage goes down to 1%.
When the limit is greater, in this case 120, CPU usage is 25%+
*/
unsigned int framerateLimit = 120;
sf::Time fpsStep = sf::milliseconds(1000 / framerateLimit);
sf::Time fpsSleep;
fpsTimer.restart();
while (window->isOpen()) {
// Update timer
fpsElapsedTime = fpsTimer.restart();
fps = 1000.0f / fpsElapsedTime.asMilliseconds();
// Update FPS text
std::stringstream ss;
ss << "FPS: " << std::fixed << std::setprecision(0) << fps;
fpsText.setString(ss.str());
// Get events
sf::Event evt;
while (window->pollEvent(evt)) {
switch (evt.type) {
case sf::Event::Closed:
window->close();
break;
default:
break;
}
}
// Draw
window->clear(sf::Color(255, 255, 255));
window->draw(fpsText);
window->display();
// Sleep
fpsSleep = fpsStep - fpsTimer.getElapsedTime();
if (fpsSleep.asMilliseconds() > 0) {
sf::sleep(fpsSleep);
}
}
return 0;
}
I don't want to use SFML's setFramerateLimit(), but my own implementation with the sleep because I will use the fps data to update my physics and stuff.
Is there a logic error in my code? I fail to see it, given it works with a framerate limit of for example 60 (or less). Is it because I have a 60 Hz monitor?
PS: Using SFML's window->setVerticalSync() doesn't change the results
Thank you