const wxml = `<view class="container" >

  <view class="item-box red">

  </view>

  <view class="item-box green" >

    <text class="text">yeah!</text>

  </view>

  ...

</view>`;

​

const {pixelRatio} = wx.getSystemInfoSync();

​

const style = {

    container: {

        width: canvasWdith * pixelRatio,

        height: canvasHeight * pixelRatio,

        backgroundColor: 'transparent',

    },

    //...

}