How to render at a fixed FPS in a GLFW window? - c++

Question

I am trying to render at 60 FPS but my scene is rendering at a much higher rate than 60 FPS.
This is my code for the Render Loop, is this the correct way to render at a desired FPS or are there better ways?
double lastTime = glfwGetTime(), timer = lastTime;
double deltaTime = 0, nowTime = 0;
int frames = 0, updates = 0;
while (!glfwWindowShouldClose(window))
{
// input
// -----
processInput(window);
// - Measure time
nowTime = glfwGetTime();
deltaTime += (nowTime - lastTime) / limitFPS; // limitFPS = 1.0 / 60.0
lastTime = nowTime;
// - Only update at 60 frames / s
while (deltaTime >= 1.0) {
updates++;
deltaTime--;
glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
w.render(); // Render function
frames++;
}
glfwPollEvents();
// - Reset after one second
if (glfwGetTime() - timer > 1.0) {
timer++;
}
glfwSwapBuffers(window);
}

Answer 1

Based on the discussion in comments above, you want to draw a maximum of 60 FPS, but you want the logic to update as often as possible. Correct?
That can be achieved with just one loop, a timer, and an if statement:
const double fpsLimit = 1.0 / 60.0;
double lastUpdateTime = 0; // number of seconds since the last loop
double lastFrameTime = 0; // number of seconds since the last frame
// This while loop repeats as fast as possible
while (!glfwWindowShouldClose(window))
{
double now = glfwGetTime();
double deltaTime = now - lastUpdateTime;
glfwPollEvents();
// update your application logic here,
// using deltaTime if necessary (for physics, tweening, etc.)
// This if-statement only executes once every 60th of a second
if ((now - lastFrameTime) >= fpsLimit)
{
// draw your frame here
glfwSwapBuffers(window);
// only set lastFrameTime when you actually draw something
lastFrameTime = now;
}
// set lastUpdateTime every iteration
lastUpdateTime = now;
}
Everything that you want to execute as often as possible should be in the outer part of that while loop, and everything you want to execute at a maximum of 60 times per second should be inside the if statement.
If the loop takes longer than 1/60th of a second to execute an iteration then your FPS and update rate will drop to whatever rate is achievable for that workload/system.