Delta Time in JavaScript

Delta time is a commonly used concept in game programming, particularly for animations and physics simulations. It refers to the elapsed time between two consecutive frames in a game loop. In JavaScript, it can be implemented using the Date object.

Getting Delta Time

To get the delta time, you need to subtract the current time from the previous time. This can be done using the getTime() method of the Date object. Here is a sample code that calculates delta time:

let previousTime = new Date().getTime();
let currentTime;
let deltaTime;

function gameLoop() {
   currentTime = new Date().getTime();
   deltaTime = (currentTime - previousTime) / 1000; // divide by 1000 to convert to seconds
   previousTime = currentTime;

   // do something with deltaTime
}

setInterval(gameLoop, 16.67); // 60 FPS

Here we have defined a game loop function that calculates deltaTime every frame. We use the setInterval function to call the game loop function at a fixed interval (16.67ms for 60 FPS).

Using Delta Time

Delta time can be used to make animations and physics simulations smoother and consistent across different hardware. Here are some examples:

Animations

let position = 0;
let speed = 100; // pixels per second

function animate() {
   position += speed * deltaTime;
   element.style.transform = `translateX(${position}px)`;
}

setInterval(animate, 16.67); // 60 FPS

Here we have a simple animation that moves an element horizontally at a constant speed of 100 pixels per second. By using deltaTime, we ensure that the animation runs smoothly regardless of the frame rate.

Physics Simulations

let position = 0;
let velocity = 0;
let acceleration = 10; // pixels per second squared

function simulate() {
   velocity += acceleration * deltaTime;
   position += velocity * deltaTime;
   element.style.transform = `translateY(${position}px)`;
}

setInterval(simulate, 16.67); // 60 FPS

Here we have a simple physics simulation that simulates an object falling due to gravity. By using deltaTime, we ensure that the simulation runs consistently across different hardware and frame rates.

Conclusion

Delta time is a useful concept in game programming that can help make animations and simulations smoother and more consistent. By using the Date object and some basic math, we can easily calculate delta time in JavaScript and use it to improve the quality of our games and applications.