onLoad: function () {
    var that=this
    // 通过 SelectorQuery 获取 Canvas 节点
    const query=wx.createSelectorQuery()
      .select('#canvas')
      .fields({
        node: true,
        size: true,
      })
      .exec(
        res=>{ 
          const canvas = res[0].node
           this.ctx = canvas.getContext('2d')
          // that.setData({
          //    ctx
          // })
          const dpr = wx.getSystemInfoSync().pixelRatio
          canvas.width = res[0].width * dpr
          canvas.height = res[0].height * dpr
          this.ctx.scale(dpr, dpr)
          this.render(canvas, this.ctx)
        }
      )
  },


  render(canvas, ctx) {
    let that = this;
    let img = canvas.createImage();//canvas 2d 通过此函数创建一个图片对象
    img.onload = (e) => {
      console.log('img loaded')
      ctx.drawImage(img, 0, 0, 300, 300);
      // wx.canvasToTempFilePath({
      //   canvas,
      //   success(res) {
      //     console.log(res.tempFilePath)
      //     that.setData({
      //       imgSrc:res.tempFilePath
      //     })
      //   }
      // }, that)
    }
    img.onerror = (e) => {
      console.error('err:', e)
    }
    img.src = './car.png'
  },


  touchStart:function(e){




    /*画圆圈
    this.ctx.arc(30,30,10,0,Math.PI*2,true)
    this.ctx.stroke()
    */


   
      this.x1=e.touches[0].x
      this.y1=e.touches[0].y
      this.ctx.beginPath()
  
  },
  touchMove:function(e){



    
      //画点
      var x2=e.touches[0].x
      var y2=e.touches[0].y
    
      this.ctx.arc(x2,y2,10,0,Math.PI*2,true)
      // this.ctx.lineTo(x2, y2)
      // this.ctx.lineWidth=5
      // this.ctx.strokeStyle="red"
      this.ctx.stroke()
      this.x1=x2
      this.y1=y2
      










     /*画线
      var x2=e.touches[0].x
      var y2=e.touches[0].y
      this.ctx.moveTo(this.x1,this.y1)
      this.ctx.lineTo(x2, y2)
      this.ctx.lineWidth=5
      this.ctx.strokeStyle="red"
      this.ctx.stroke()
      this.x1=x2
      this.y1=y2
      */
  },
  touchEnd:function(e){