Time-passed check with Pause functionality

Question

I am working on a game that has a lot of time-passed checks of the following format. These work great, but there is a problem when the game is paused:

If paused for any meaningful amount of time, the if statement will become true.

const t = new Date().getTime(); // Get the current time (in ms)
const fireCooldown = 500; // The time to wait before firing again (in ms)

if(t > lastFireTime + fireCooldown) {
   lastFireTime = t;
   fire();
}

How can I integrate pause functionality into this - in a way where pausing does not make the if statement true?

Answer 1

The usual way to handle this it to separate the notion of "game time" from "real time".

While the game is running, you increase your game time variable's value each frame / simulation step.

Scripts that need a timestamp to work with will read the current value of that game time variable.

When your game is paused, you disable the code that increases the game time variable. Now for anything that's checking timestamps in game time, it's as though time has frozen — exactly what you want.

The challenge often comes in due to the fact that you don't want everything to pause. Animations in the UI like the pause menu should still play. So you need to set up your scripts to read either realtime or game time based on their context.

As a bonus, tracking game time this way also lets you enable slow motion and (some) fast forward effects, by just scaling how much you add to the game time variable you can alter the perceived flow of time for all scripts that use it.