纯JavaScript动画缓动

Question

几个小时以来，我一直在努力寻找一个纯粹的 JavaScript 简易实现，但找不到。那些接近的没有任何意义。我所能找到的只是一堆没有实现的缓动函数。

例如，像这样的函数：

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

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

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

困扰我的一件事是fps在哪里发挥作用？它与持续时间直接相关。我没看到有人提到它。

如何在下面的动画中实现上述缓动函数？

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>

Answer 1

您可以使用 time 变量并为每一帧增加它，并使用缓动函数在正确的位置使用您已有的值。

缓动公式：http://easings.net/
说明：What is an easing function?

// formula     http://easings.net/
// description 
// 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>

Answer 2

<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>

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