11

I've been trying to find a pure JavaScript ease implementation for some hours, but couldn't find any. The ones that came close didn't make any sense. All I could find was bunch of easing functions without implementation.

For example, functions like these:

function linear(time, begin, change, duration) {
    return change * time / duration + begin;
}

function easeInQuad(t) {
    return t*t
},

function easeOutQuad(t) {
    return t*(2-t)
},

One of the things that trouble me is where does fps come in to play? It's directly related to the duration. I've seen no mention of it.

How would I implement the above easing functions in the following animation?

JSFiddle

var box = document.getElementById("box");

var fps  = 60;
var duration = 2; // seconds
var start = 0; // pixel
var finish = window.innerWidth - box.clientWidth;
var distance = finish - start;
var increment = distance / (duration * fps);

var position = start;

function move() {
  position += increment;
  if (position >= finish) {
    clearInterval(handler);
    box.style.left = finish + "px";
    return;
  }
  box.style.left = position + "px";
}

var handler = setInterval(move, 1000 / fps);
body {
  background: gainsboro;
}
#box {
  width: 100px;
  height: 100px;
  background: white;
  box-shadow: 1px 1px 1px rgba(0, 0, 0, .2);
  position: absolute;
  left: 0;
}
<div id="box"></div>
akinuri
  • 10,690
  • 10
  • 65
  • 102

2 Answers2

20

You could use a time variable and increment it for every frame and use the easing functions for the right position with the values you already have.

// formula     http://easings.net/
// description https://stackoverflow.com/questions/8316882/what-is-an-easing-function
// x: percent
// t: current time,
// b: beginning value,
// c: change in value,
// d: duration
function easeInOutQuad(x, t, b, c, d) {
    if ((t /= d / 2) < 1) {
        return c / 2 * t * t + b;
    } else {
        return -c / 2 * ((--t) * (t - 2) - 1) + b;
    }
}

function move() {
    //position += increment;
    time += 1 / fps;
    position = easeInOutQuad(time * 100 / duration, time, start, finish, duration);

    if (position >= finish) {
        clearInterval(handler);
        box.style.left = finish + "px";
        return;
    }
    box.style.left = position + "px";
}

var box = document.getElementById("box"),
    fps = 60,
    duration = 2, // seconds
    start = 0, // pixel
    finish = window.innerWidth - box.clientWidth,
    distance = finish - start,
    increment = distance / (duration * fps),
    position = start,
    time = 0,
    handler = setInterval(move, 1000 / fps);
body {
  background: gainsboro;
}
#box {
  width: 100px;
  height: 100px;
  background: white;
  box-shadow: 1px 1px 1px rgba(0, 0, 0, .2);
  position: absolute;
  left: 0;
}
<div id="box"></div>
Community
  • 1
  • 1
Nina Scholz
  • 376,160
  • 25
  • 347
  • 392
  • 2
    I've posted an [answer](http://stackoverflow.com/questions/8316882/what-is-an-easing-function/38513962#38513962) on [What is an easing function?](http://stackoverflow.com/questions/8316882/what-is-an-easing-function/38513962#38513962) about the implementation. Since you've helped me on the subject, thought you might want to know :) – akinuri Jul 21 '16 at 20:49
  • Maybe it'd be better to be able to chose easing functions, like sigmoid, linear, and quadratic, and even like bezier. – martian17 Jun 05 '20 at 21:16
0

<canvas id='canvas' width=600 height=400></canvas>

<script>
  var ctx = document.getElementById('canvas').getContext('2d');
  var divx = 500;
  var divtx = 0;

  function animate() {
    divx += (divtx - divx) / 20;
    ctx.clearRect(0, 0, 600, 400);
    ctx.fillRect(divx, 0, 100, 100);
    window.requestAnimationFrame(animate);
  }
  animate();
</script>
adiga
  • 34,372
  • 9
  • 61
  • 83
Ahmad Faisal Jawed
  • 11