阻尼函数 h5 应用
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0,maximum-scale=1.0,user-scalable=0">
<style>
body, ul {
margin: 0;
padding: 0;
}
ul {
list-style: none;
}
.wrapper {
position: absolute;
top: 50%;
left: 0;
right: 0;
margin: 0 auto;
height: 80%;
width: 80%;
max-width: 300px;
max-height: 500px;
border: 1px solid #000;
transform: translateY(-50%);
overflow: hidden;
}
.list {
background-color: #70f3b7;
transition-timing-function: cubic-bezier(.165, .84, .44, 1);
}
.list-item {
height: 40px;
line-height: 40px;
width: 100%;
text-align: center;
border-bottom: 1px solid #ccc;
}
</style>
</head>
<body>
<div id="app"></div>
<template id="tpl">
<div
class="wrapper"
ref="wrapper"
@touchstart.prevent="onStart"
@touchmove.prevent="onMove"
@touchend.prevent="onEnd"
@touchcancel.prevent="onEnd">
<ul
class="list"
ref="scroller"
:style="scrollerStyle">
<li
class="list-item"
v-for="item in list">
{{item}}
</li>
</ul>
</div>
</template>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<script>
new Vue({
el: '#app',
template: '#tpl',
computed: {
list() {
const list = [];
for (let i = 0; i < 100; i++) {
list.push(i);
}
return list;
},
scrollerStyle() {
return {
'transform': `translate3d(0, ${this.offsetY}px, 0)`,
'transition-duration': `${this.duration}ms`,
};
},
},
data() {
return {
wrapper: null,
scroller: null,
minY: 0,
maxY: 0,
wrapperHeight: 0,
offsetY: 0,
duration: 0,
pos: {},
cacheOffsetY: 0,
};
},
mounted() {
this.$nextTick(() => {
this.wrapper = this.$refs.wrapper;
this.scroller = this.$refs.scroller;
const { height: wrapperHeight } = this.wrapper.getBoundingClientRect();
const { height: scrollHeight } = this.scroller.getBoundingClientRect();
this.wrapperHeight = wrapperHeight;
this.minY = wrapperHeight - scrollHeight;
});
},
methods: {
onStart(e) {
this.duration = 0;
this.stop();
// 是否为第一个触点，若是则需要重置 cacheOffsetY 值
let isFirstTouch = true;
Array.from(e.touches).forEach(touch => {
const id = touch.identifier;
if (!this.pos[id]) {
this.pos[id] = touch.pageY;
return;
}
isFirstTouch = false;
});
if (isFirstTouch) {
this.cacheOffsetY = this.offsetY;
}
},
onMove(e) {
let offset = 0;
Array.from(e.touches).forEach(touch => {
const id = touch.identifier;
if (this.pos[id]) {
offset += Math.round(touch.pageY - this.pos[id]);
}
});
offset = this.cacheOffsetY + offset;
// 超出边界时增加阻尼效果
if (offset < this.minY || offset > this.maxY) {
this.offsetY = this.damping(offset, this.wrapperHeight);
} else {
this.offsetY = offset;
}
},
onEnd(e) {
Array.from(e.changedTouches).forEach(touch => {
const id = touch.identifier;
if (this.pos[id]) {
this.cacheOffsetY += Math.round(touch.pageY - this.pos[id]);
}
});
// 当所有触点都离开平面
if (!e.touches.length) {
this.cacheOffsetY = 0;
this.pos = {};
this.resetPosition();
}
},
stop() {
// 获取当前 translate 的位置
const matrix = window.getComputedStyle(this.scroller).getPropertyValue('transform');
this.offsetY = Math.round(+matrix.split(')')[0].split(', ')[5]);
},
// 超出边界时重置位置
resetPosition() {
let offsetY;
if (this.offsetY < this.minY) {
offsetY = this.minY;
} else if (this.offsetY > this.maxY) {
offsetY = this.maxY;
}
if (typeof offsetY !== 'undefined') {
this.offsetY = offsetY;
this.duration = 500;
}
},
// 阻尼函数
damping(x, max) {
let y = Math.abs(x);
y = 0.82231 * max / (1 + 4338.47 / Math.pow(y, 1.14791));
return Math.round(x < 0 ? -y : y);
},
},
});
</script>
</body>
</html>
