Glm rotate object by time

Question

I have an object which I want to rotate on key hold using this function

if (key == GLFW_KEY_S && action == GLFW_REPEAT) {
            timer = glfwGetTime();
}

Which sends timer to this rotation

auto rotateMat = rotate(mat4{}, timer * 0.4f, {0, 1, 0});

But problem is, I hold key S pressed and the object is rotating but when I release it, time is changing of course, since glfwGetTime() gets real time. Then I press S again and hold it to rotate, but it starts rotation from different object angle as when it stopped. Any ideas how to fix it?

EDIT:

I have fixed it by using timer += 0.1;

But when I press S and hold it, it has a delay about 1 second until the object starts rotating. It was same with using real glfwGetTime(). How can I have no delay?

Answer 1

You should track if the key is pressed:

if (action == GLFM_PRESS) {
    keysPressed[key] = true;
}
if (action == GLFM_RELEASE) {
    keysPressed[key] = false;
}

In the render loop:

now = glfwGetTime();
double delta = now - lastTime;
lastTime = now;

if (keysPressed[GLFW_KEY_S]) {
    timer += delta;
}
if (keysPressed[GLFW_KEY_A]) {
    timer -= delta;
}
auto rotateMat = rotate(mat4{}, timer * 0.4f, {0, 1, 0});