Detailed explanation of tween.js easing tween animation algorithm

This article mainly introduces you to the tween.js easing tweening animation example. The editor thinks it is quite good, so I will share it with you now and give it as a reference. Let’s follow the editor to take a look, I hope it can help everyone.

1. Understanding tween.js

If you understand the above, you can skip the following part. The following is an explanation of Tween.js. Let’s introduce how to use this Tween. First, the three parameters b, c, and d (i.e. initial value, change amount, duration) need to be determined before easing starts. First, introduce a concept of tweening animation. Flash uses the Tween class when doing animations. It can be used to create many animation effects, such as easing, spring, etc. tween.js can be interpreted as tweening animation in Flash. So the question is, what is tweening animation?

I believe everyone who has studied Flash knows that tweening animation is the main and very important means of expression in Flash. 1. There are two types of tweening animation: action tweening animation and shape tweening animation, but you don’t need to know so much about it in js. Okay, without further ado, let’s take a look at Baidu Encyclopedia’s information about tweening animation. Definition: Tween animation: When doing flash animation, "tweening animation" needs to be done between two key frames to realize the movement of the picture; after inserting the tweening animation, the interpolation frame between the two key frames is automatically generated by the computer.

obtained by calculation. So what are key frames? For example: Let’s do some science first. The movies and animations we usually watch are all 24 frames, and 24 frames are one second. The human eye can capture Within the range. You can imagine that there are 22 points between the two points, forming a straight line or curve. Each point represents a frame, and a frame is the smallest unit of a single image in animation, and a single image It can be regarded as an object (everything is an object, except value types). And this line represents the movement trajectory of the object.

Two and four parameters

1. t: current time--> represents the first point, which is the first frame, which is where an animation starts.

2. b: beginning value--> represents the initial value, which is the starting amount. When we watch movies or animations, we generally don’t watch the prologue, so skip the beginning and select the first part. You want to start looking at the position between the first frame and the last frame, and this position is the initial value.

3. c: change in value-->Represents the change in the last frame minus the initial value,

4. d: duration -->Represents the last frame, the end of 1s, and the end of the animation.

Usage of tween.js 1. Download 2. Import 3. Use tween.js syntax

Tween. Easing function name. Easing effect name (t, b,c,d);

Note: When the number of starting steps is increased to be equal to the number of ending steps, the entire movement ends. Note: The movement will only end when t is increased to be equal to d; if If you don’t wait, the movement will not stop.

3. tween file code

/*
 * Tween.js
 * t: current time（当前时间）；
 * b: beginning value（初始值）；
 * c: change in value（变化量）；
 * d: duration（持续时间）。
*/
var Tween = {
  Linear: function(t, b, c, d) { //匀速
    return c * t / d + b; 
  },
  Quad: { //二次方缓动效果
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t + b;
    },
    easeOut: function(t, b, c, d) {
      return -c *(t /= d)*(t-2) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t + b;
      return -c / 2 * ((--t) * (t-2) - 1) + b;
    }
  },
  Cubic: { //三次方缓动效果
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t + b;
    },
    easeOut: function(t, b, c, d) {
      return c * ((t = t/d - 1) * t * t + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t*t + b;
      return c / 2*((t -= 2) * t * t + 2) + b;
    }
  },
  Quart: { //四次方缓动效果
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t*t + b;
    },
    easeOut: function(t, b, c, d) {
      return -c * ((t = t/d - 1) * t * t*t - 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;
      return -c / 2 * ((t -= 2) * t * t*t - 2) + b;
    }
  },
  Quint: { //五次方缓动效果
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t * t * t + b;
    },
    easeOut: function(t, b, c, d) {
      return c * ((t = t/d - 1) * t * t * t * t + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;
      return c / 2*((t -= 2) * t * t * t * t + 2) + b;
    }
  },
  Sine: { //正弦缓动效果
    easeIn: function(t, b, c, d) {
      return -c * Math.cos(t/d * (Math.PI/2)) + c + b;
    },
    easeOut: function(t, b, c, d) {
      return c * Math.sin(t/d * (Math.PI/2)) + b;
    },
    easeInOut: function(t, b, c, d) {
      return -c / 2 * (Math.cos(Math.PI * t/d) - 1) + b;
    }
  },
  Expo: { //指数缓动效果
    easeIn: function(t, b, c, d) {
      return (t==0) ? b : c * Math.pow(2, 10 * (t/d - 1)) + b;
    },
    easeOut: function(t, b, c, d) {
      return (t==d) ? b + c : c * (-Math.pow(2, -10 * t/d) + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if (t==0) return b;
      if (t==d) return b+c;
      if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
      return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
    }
  },
  Circ: { //圆形缓动函数
    easeIn: function(t, b, c, d) {
      return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
    },
    easeOut: function(t, b, c, d) {
      return c * Math.sqrt(1 - (t = t/d - 1) * t) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
      return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
    }
  },
  Elastic: { //指数衰减正弦曲线缓动函数
    easeIn: function(t, b, c, d, a, p) { //加速
      var s;
      if (t==0) return b;
      if ((t /= d) == 1) return b + c;
      if (typeof p == "undefined") p = d * .3;
      if (!a || a < Math.abs(c)) {
        s = p / 4;
        a = c;
      } else {
        s = p / (2 * Math.PI) * Math.asin(c / a);
      }
      return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
    },
    easeOut: function(t, b, c, d, a, p) { //减速
      var s;
      if (t==0) return b;
      if ((t /= d) == 1) return b + c;
      if (typeof p == "undefined") p = d * .3;
      if (!a || a < Math.abs(c)) {
        a = c; 
        s = p / 4;
      } else {
        s = p/(2*Math.PI) * Math.asin(c/a);
      }
      return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b);
    },
    easeInOut: function(t, b, c, d, a, p) { //先加速后减速
      var s;
      if (t==0) return b;
      if ((t /= d / 2) == 2) return b+c;
      if (typeof p == "undefined") p = d * (.3 * 1.5);
      if (!a || a < Math.abs(c)) {
        a = c; 
        s = p / 4;
      } else {
        s = p / (2 *Math.PI) * Math.asin(c / a);
      }
      if (t < 1) return -.5 * (a * Math.pow(2, 10* (t -=1 )) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
      return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p ) * .5 + c + b;
    }
  },
  Back: { //超过范围的三次方的缓动函数
    easeIn: function(t, b, c, d, s) {
      if (typeof s == "undefined") s = 1.70158;
      return c * (t /= d) * t * ((s + 1) * t - s) + b;
    },
    easeOut: function(t, b, c, d, s) {
      if (typeof s == "undefined") s = 1.70158;
      return c * ((t = t/d - 1) * t * ((s + 1) * t + s) + 1) + b;
    },
    easeInOut: function(t, b, c, d, s) {
      if (typeof s == "undefined") s = 1.70158; 
      if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;
      return c / 2*((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;
    }
  },
  Bounce: { //指数衰减的反弹曲线缓动函数
    easeIn: function(t, b, c, d) {
      return c - Tween.Bounce.easeOut(d-t, 0, c, d) + b;
    },
    easeOut: function(t, b, c, d) {
      if ((t /= d) < (1 / 2.75)) {
        return c * (7.5625 * t * t) + b;
      } else if (t < (2 / 2.75)) {
        return c * (7.5625 * (t -= (1.5 / 2.75)) * t + .75) + b;
      } else if (t < (2.5 / 2.75)) {
        return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b;
      } else {
        return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b;
      }
    },
    easeInOut: function(t, b, c, d) {
      if (t < d / 2) {
        return Tween.Bounce.easeIn(t * 2, 0, c, d) * .5 + b;
      } else {
        return Tween.Bounce.easeOut(t * 2 - d, 0, c, d) * .5 + c * .5 + b;
      }
    }
  }
}
Math.tween = Tween;

4. Give a chestnut

<!DOCTYPE html>
<html>

  <head>
    <meta charset="UTF-8">
    <title></title>
    <script src="https://cdn.jsdelivr.net/npm/vue"></script>
    <script src="Tween/tween.js"></script>
    <style>
      *{margin: 0;padding: 0;}
      .out{width: 800px;height: 500px;background: #e5e5e5;position: relative;padding: 20px;text-align: center;}
      .inner{width: 50px;height: 50px;border-radius: 50%;background: #FF0000; position: absolute;left: 50px;top: 50px;}
    </style>
  </head>

  <body>
    <p id="app" class="out">
      <p class="inner" id="ball"></p>
      <button id="start" @click="start()">start</button>
    </p>
  </body>
  <script type="text/javascript">
    var app = new Vue({
      el: '#app',
      data: {
        t: 0,
        b: 50,
        c: 500,
        d: 1500,
      },
      methods:{
        start(){
          var t = this.t;
          const b = this.b;
          const c = this.c;
          const d = this.d;
          const setInt = setInterval(()=>{
            t++;
            console.log(t)
            if(t==300){clearInterval(setInt)}
            console.log(t);
            const ballLeft = Tween.Linear(t,b,c,d)+"px";
            ball.style.left = ballLeft;
          },20)
        }
      }
    })
  </script>
</html>

5. Personal experience

The advantage of tween is that the effect of tween is based on an algorithm, not the grammar of a certain language, so it can be used in a wide range of places, and you will benefit from it once you learn it.

Related recommendations:

Detailed explanation of usage examples of tween.js

Simple animation library encapsulation tween.js example tutorial

Tween.js animation detailed introduction

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