场景是有两个canvas2D，重叠放置， 一个渲染静态的场景资源，放在下层， 一个是需要高频率渲染与用户的交互，放在上层， 可以将上层的canvas2D背景设置为透明吗？

 touchEnd(e){//TODO:复位       if(this._pointCountInScreenLessThanFive(tempSeat)){         let boxModel = this._getBoxModel(tempSeat)         let direction = this._computeRestDirection(boxModel)          this._reset(direction)       }     },  _reset(direction){       if(this._pointCountInScreenLessThanFive(tempSeat)){         this._updata(tempSeat,direction)         this._render(tempSeat,{})         this.canvas.requestAnimationFrame(this._reset)       }     }, VM6312 WAService.js:2 MiniProgramError Cannot read property '_pointCountInScreenLessThanFive' of undefined TypeError: Cannot read property '_pointCountInScreenLessThanFive' of undefined     at _reset (http://127.0.0.1:57867/appservice/components/seatMap/index.js:414:16) tempSeat是在当前页面下模拟的全局变量，试验用 如蒙赐教，感激不尽！

selectSeat:function(e){       const clickX = e.detail.x       const clickY = e.detail.y             const ctx = this.context      ctx.beginPath()      ctx.rect(200,0,100,100)      ctx.closePath()      ctx.stroke()            console.log(ctx.isPointInPath(clickX,clickY),clickX,clickY)     } [图片]

_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)     } [图片]