<view class="container">
 <!-- 剪裁框与初始图片，剪裁框监听用户手势，获取移动缩放旋转值，images通过css样式显示变化 -->
 <view class="img" style="width:{{ width }}px; height:{{height}}px" catchtouchstart="touchstartCallback" catchtouchmove="touchmoveCallback" catchtouchend="touchendCallback" >
  <image style="transform: translate({{stv.offsetX}}px, {{stv.offsetY}}px) scale({{stv.scale}}) rotate({{ stv.rotate }}deg);width:{{originImg.width}}px; height: {{originImg.height}}px" src="{{ originImg.url }}"></image>
 </view>
 <view class='footer'>
   <view bindtap='uploadTap'>选择图片</view> 
   <view bindtap='rotate'>旋转</view>
   <view bindtap='cropperImg'>剪裁</view>
 </view>
 
 <!-- canvas长宽设为初始图片设置的长款的两倍，使剪裁得到的图片更清晰，也不至于过大 -->
 <canvas class='imgcrop' style="width:{{ width * 2 }}px;height:{{ height * 2}}px;" canvas-id='imgcrop'></canvas>
</view>

let ctx = wx.createCanvasContext('imgcrop',this);
   let cropData = _this.data.stv;
   ctx.save();
   // 缩放偏移值
   let x = (_this.data.originImg.width - _this.data.originImg.width * cropData.scale) / 2;
   let y = (_this.data.originImg.height - _this.data.originImg.height * cropData.scale) / 2;
 
   //画布中点坐标转移到图片中心
   let movex = (cropData.offsetX + x) * 2 + _this.data.originImg.width * cropData.scale;
   let movey = (cropData.offsetY + y) * 2 + _this.data.originImg.height * cropData.scale;
   ctx.translate(movex, movey);
   ctx.rotate(cropData.rotate * Math.PI / 180);
   ctx.translate(-movex, -movey);
    
   ctx.drawImage(_this.data.originImg.url, (cropData.offsetX + x) * 2, (cropData.offsetY + y) * 2, _this.data.originImg.width * 2 * cropData.scale, _this.data.originImg.height * 2 * cropData.scale);
   ctx.restore();