_initCanvas:function(){
      const q = wx.createSelectorQuery().in(this)
      q.select("#seatMap")
      .fields({ node : true , size : true})
      .exec(res=>{
        const canvas = res[0].node
        const context = canvas.getContext("2d")
        const dpr = wx.getSystemInfoSync().pixelRatio
        const phoneInfo = wx.getSystemInfoSync()
        const canvasHeight = phoneInfo.windowHeight *dpr
        const canvasWidth = phoneInfo.windowWidth * dpr
        const statusBarHeight = phoneInfo.statusBarHeight * dpr
        canvas.width = canvasWidth 
        canvas.height = canvasHeight 


        this.setData({
          canvas,
          context,
          canvasHeight,
          canvasWidth,
          statusBarHeight
        })


        context.scale(dpr,dpr)
        context.font="20px sans-serif"
        context.fillText("welcome",100,100)
        context.strokeRect(0,0,300,300)


      })
      console.log(this.data.context)
    }