uni-app拖拽悬浮球优化

使用uni-app拖拽悬浮球，插件不错 ，插件地址 ext.dcloud.net.cn/plugin?id=5…

插件挺不错的，有几点需求我改了下
1、背景图片保持纵横比缩放图片，使用aspectFit好点
2、初始化球位置时使用%比较符合实际，如果放到右底部使用px还要适配
3、拖拽超出边框没有做限制。

<template>
    <view class="holdon" >
        <image  class="ball" :style="'left:'+(moveX == 0 & x>0? x+'%':moveX+'px')+';top:'+(moveY == 0 & y>0? y+'%':moveY+'px')"     
                @touchstart="drag_start" @touchmove.prevent="drag_hmove" :src="image"  mode="aspectFit">
        </image>
    </view>
</template>
<script>
    export default {
        props: {
            x: {
                type: Number,
                default:0
            },
            y: {
                type: Number,
                default:0
            },
            image:{
                type:String,
                default: ''
            }
        },
        data() {
            return {
                start:[0,0],
                moveY:0,
                moveX:0,
                windowWidth:'',
                windowHeight:'',
            }
        },
        mounted() {
            const { windowWidth, windowHeight } = uni.getSystemInfoSync();    
            this.windowWidth = windowWidth
            this.windowHeight = windowHeight
        },
        methods: {
            drag_start(event){
                this.start[0]= event.touches[0].clientX-event.target.offsetLeft;
                this.start[1]= event.touches[0].clientY-event.target.offsetTop;
            },
            drag_hmove(event){
                    let     tag      = event.touches;
                    if(tag[0].clientX < 0 ){
                        tag[0].clientX = 0
                    }
                    if(tag[0].clientY < 0 ){
                        tag[0].clientY = 0
                    }
                    if(tag[0].clientX > this.windowWidth ){
                        tag[0].clientX = this.windowWidth
                    }
                    if(tag[0].clientY > this.windowHeight ){
                        tag[0].clientY = this.windowHeight
                    }
                    this.moveX     = tag[0].clientX-this.start[0];
                    this.moveY     = tag[0].clientY-this.start[1];
            }
        }}
</script>
 
<style lang="less">
    .holdon{
         100%;
        height: 100%;
    }
    .ball{
         70upx;height: 70upx;
        background:linear-gradient(to bottom, #F8F8FF,#87CEFA);
        border-radius: 50%;
        box-shadow: 0 0 15upx #87CEFA;
        color: #fff;
        font-size: 30upx;
        display: flex;justify-content: center;align-items: center;
        position: fixed !important;
        z-index: 1000000;
    }
</style>