小程序如何实现图片移动缩放

/**
 * All right by NieYinlong
 */

Page({

 /**
 * 页面的初始数据
 */
 data: {
 bgBoxHeight: 400, // 背景的高度
 bgBoxWidth: 320, // 背景的宽度
 
 moveImgLeft: 40,
 moveImgTop: 80,
 moveImgH: 100,
 moveImgW: 100,

 scaleIconFixWidth: 30,
 scaleLeft: 0,    // 拉伸按钮默认x坐标 (拉伸按钮默认宽高30)
 scaleTop: 0,    // 拉伸按钮默认y坐标
 },

 /**
 * 生命周期函数--监听页面加载
 */
 onLoad: function (options) {
 const halfWidth = this.data.scaleIconFixWidth / 2
 this.setData({
  scaleLeft: this.data.moveImgLeft + this.data.moveImgW - halfWidth,
  scaleTop: this.data.moveImgTop + this.data.moveImgH - halfWidth
 })
 },

 // 图片移动
 moveImgTouchmove: function(e) {
 console.log(e)
 let pageX = e.changedTouches[0].pageX
 let pageY = e.changedTouches[0].pageY
 
 
 // (this.data.moveImgW / 2)是因为触摸放到中间位置
 let toLeft = pageX - this.data.moveImgW / 2; 
 let toTop = pageY - this.data.moveImgH / 2;

 const halfWidth = this.data.scaleIconFixWidth / 2

 // 限制x左边不能出边框
 if (pageX - (this.data.moveImgW / 2) <= 0) {
  return;
 }
 
 // 限制右边不能出超过边框
 if ((pageX + (this.data.moveImgW / 2)) >= (this.data.bgBoxWidth)) {
  return;
 }

 // 限制top
 if (pageY - (this.data.moveImgH / 2) <= 1) {
  return;
 }

 // 限制bottom
 if ((pageY + (this.data.moveImgH / 2)) >= this.data.bgBoxHeight) {
  return;
 }


 this.setData({
  moveImgLeft: toLeft,
  moveImgTop: toTop,
  scaleLeft: toLeft + this.data.moveImgW - halfWidth,
  scaleTop: toTop + this.data.moveImgH - halfWidth
 })
 },
 
 // 拉伸按钮移动
 scaleTouchmove: function (e) {
 console.log(e)
 let pageX = e.changedTouches[0].pageX
 let pageY = e.changedTouches[0].pageY
 const halfWidth = this.data.scaleIconFixWidth / 2
 let toLeft = pageX - halfWidth // 减去halfWidth是拉伸按钮宽度的一半
 let toTop = pageY - halfWidth

 
 let changedW = pageX - this.data.moveImgLeft
 let changedH = pageY - this.data.moveImgTop

 // 限制最moveImg小尺寸
 if (toLeft <= (this.data.moveImgLeft + halfWidth)) {
  return;
 }
 if (toTop <= (this.data.moveImgTop + halfWidth)) {
  return;
 }

 // 限制moveImg最大尺寸
 if(pageX - this.data.moveImgLeft > 250) {
  // 宽度达到最大值
  return;
 }
 if (pageY - this.data.moveImgTop > 250) {
  // 高度达到最大值
  return;
 }

 // 限制拉伸按钮的right
 if(this.data.scaleLeft + this.data.scaleIconFixWidth >= this.data.bgBoxWidth) {
  return;
 }
 // 限制拉伸按钮的bottom
 if (this.data.scaleTop + this.data.scaleIconFixWidth >= this.data.bgBoxHeight) {
  return;
 }

 this.setData({
  scaleLeft: toLeft,
  scaleTop: toTop,
  moveImgW: pageX - this.data.moveImgLeft,
  moveImgH: pageY - this.data.moveImgTop,
 })
 },

})

.bgBox {
 border: 2px solid green;
 height: 400px;
 width: 99vw;
}

.movedImg {
 position: absolute;
 border: 3px dotted rgb(255, 166, 0);
}

.scaleIcon {
 position: absolute;
}