WeChat アプレット画像内の領域を選択してトリミング機能を実装する方法のチュートリアル

<view class="index_all_box">
 <view class="imgCut_header">
 <view class="imgCut_header_l" bindtap=&#39;okCutImg&#39;>开始裁剪</view>
 <view class="imgCut_header_m" bindtap=&#39;clickUpImg&#39;>点击上传图片</view>
 <view class="imgCut_header_r" bindtap=&#39;okBtn&#39;>点击确认</view>
 </view>
 <!-- 选择裁剪模式 -->
 <view class="selectCutMode" wx:if=&#39;{{alreay}}&#39;>
 <view class="selectCutMode_in {{cutType?&#39;selectCutMode_in_act&#39;:&#39;&#39;}}" bindtap=&#39;etcType&#39;>
  等屏裁剪
 </view>
 <view class="selectCutMode_in {{!cutType?&#39;selectCutMode_in_act&#39;:&#39;&#39;}}" bindtap=&#39;areaType&#39;>
  区域裁剪
 </view>
 </view>
 <view class="areaSelct_box" wx:if=&#39;{{!cutType && alreay}}&#39;>
 <slider bindchange="areaChange" min="50" max="100" show-value value=&#39;{{propor}}&#39;/>
 </view>
 <view class="cutImg_box" wx:if=&#39;{{!prienFlag}}&#39;>
 <view class="cutImg_box_t">
  <image src="{{cutImgUrl}}" mode=&#39;widthFix&#39;></image>
 </view>
 <view class="clickCutImg_txt" bindtap=&#39;againBtn&#39;>重新裁剪</view>
 </view>
 <view class="allCavans" wx:if=&#39;{{prienFlag}}&#39; style=&#39;width: {{canvasW}}px;height: {{canvasH}}px&#39; >
 <canvas class=&#39;canvasSty&#39; style=&#39;width: {{canvasW}}px;height: {{canvasH}}px&#39; canvas-id=&#39;cutImg&#39; disable-scroll=&#39;true&#39; bindtouchmove=&#39;canvasMove&#39;></canvas>
 <view class="allCavans_inbg" style=&#39;width: {{canvasW}}px;height:{{canvasH}}px; background: url({{img}});background-size: 100% 100%&#39;></view>
 </view>
 
 
</view>

.imgCut_header{
 padding: 30rpx;
 display: flex;
 justify-content: space-between;
 align-items: center;
 background: #000;
 color: #fff;
 font-size: 24rpx;
}
.allCavans{
 margin: 20rpx auto;
 position: relative;
}
.canvasSty{
 position: absolute;
}
.cutImg_box{
 width: 100%;
 
 border-bottom: 2rpx #f98700 solid;
 padding-bottom: 20rpx;
}
.cutImg_box .cutImg_box_t{
 width: 90%;
 margin: 20rpx auto;
}
.cutImg_box image{
 width: 100%;
}
.cutImg_box .cutImg_box_b{
 margin-top: 20rpx;
 width: 80%;
 height: 80rpx;
 line-height: 80rpx;
 background: #f98700;
 color: #fff;
 border-radius: 10rpx;
 text-align: center;
 margin:0rpx auto;
}
.selectCutMode{
 background: #fff;
 display: flex;
 justify-content: space-between;
 align-items: center;
}
.selectCutMode .selectCutMode_in{
 width: 100%;
 text-align: center;
 background: #fff;
 color: #f98700;
 font-size: 24rpx;
 padding: 20rpx;
}
.selectCutMode .selectCutMode_in_act{
 background: #f98700;
 color: #fff;
 padding: 20rpx;
}
.areaSelct_box{
 width: 100%;
 display: flex;
 align-items: center;
 height: 50rpx;
 justify-content: center;
 margin-top: 20rpx;
}
.areaSelct_box slider{
 width: 80%;
}
.cutImg_box .clickCutImg_txt{
 width: 100%;
 text-align: center;
 height: 50rpx;
 font-size: 24rpx;
 line-height: 50rpx;
 color: #999;
}

onLoad: function (options) {
  var that = this;
  const ctx = wx.createCanvasContext('cutImg');
  ctx.setGlobalAlpha(0.4)
  var aa = &#39;https://pintuanqu.oss-cn-hangzhou.aliyuncs.com/Uploads/Picture/goodsShow/20171201/5a2125fc86566.png&#39;<br />　　//获取当前屏幕宽度
  var phoneW = Number(util.nowPhoneWH()[0]*90)/100;
  var cutH = 150;
  wx.getImageInfo({
   src: aa,
   success: function (res) {
    var w = phoneW;
    var h = (phoneW/Number(res.width))*Number(res.height)
    ctx.save() 
    ctx.drawImage(aa, 0, 0, w, h)
    ctx.restore()
    ctx.setFillStyle(&#39;red&#39;)
    ctx.fillRect(0, 0, phoneW, cutH)
    ctx.draw()
    that.setData({
     canvasW:w,
     canvasH:h,
     img:aa,
     cutH:cutH
    })
   }
  })
 },