Page({
  data: {
    touch: {
      distance: 0,
      scale: 1,
      baseWidth: null,
      baseHeight: null,
      scaleWidth: null,
      scaleHeight: null
    }
  },
  touchstartCallback: function(e) {
    // 單手指縮放開始，也不做任何處理
    if(e.touches.length == 1) return
    console.log('雙手指觸發(fā)開始')
    // 注意touchstartCallback 真正代碼的開始
    // 一開始我并沒有這個回調(diào)函數(shù)，會出現(xiàn)縮小的時候有瞬間被放大過程的bug
    // 當兩根手指放上去的時候，就將distance 初始化。
    let xMove = e.touches[1].clientX - e.touches[0].clientX;
    let yMove = e.touches[1].clientY - e.touches[0].clientY;
    let distance = Math.sqrt(xMove * xMove + yMove * yMove);
    this.setData({
      'touch.distance': distance,
    })
  },
  touchmoveCallback: function(e) {
    let touch = this.data.touch
    // 單手指縮放我們不做任何操作
    if(e.touches.length == 1) return
    console.log('雙手指運動')
    let xMove = e.touches[1].clientX - e.touches[0].clientX;
    let yMove = e.touches[1].clientY - e.touches[0].clientY;
    // 新的 ditance
    let distance = Math.sqrt(xMove * xMove + yMove * yMove);
    let distanceDiff = distance - touch.distance;
    let newScale = touch.scale + 0.005 * distanceDiff
    // 為了防止縮放得太大，所以scale需要限制，同理最小值也是
    if(newScale >= 2) {
      newScale = 2
    }
    if(newScale <= 0.6) {
      newScale = 0.6
    }
    let scaleWidth = newScale * touch.baseWidth
    let scaleHeight = newScale * touch.baseHeight
    // 賦值 新的 => 舊的
    this.setData({
      'touch.distance': distance,
      'touch.scale': newScale,
      'touch.scaleWidth': scaleWidth,
      'touch.scaleHeight': scaleHeight,
      'touch.diff': distanceDiff
    })
  },
  bindload: function(e) {
   // bindload 這個api是<image>組件的api類似<img>的onload屬性
   this.setData({
     'touch.baseWidth': e.detail.width,
     'touch.baseHeight': e.detail.height,
     'touch.scaleWidth': e.detail.width,
     'touch.scaleHeight': e.detail.height
   })
  }
})

<view class="container">
  <view bindtouchmove="touchmoveCallback" bindtouchstart="touchstartCallback">
    <image src="../../resources/pic/cat.jpg"  bindload="bindload"></image>
  </view>
</view>