uniapp中canvas绘制图片内容空白报错的原因及解决

<canvas class="canvas" canvas-id="canvas"
				:style="{ height: canvasHeight + 'px', width: canvasWidth + 'px'  }"></canvas>

 //默认初始值   canvasWidth1  canvasHeight1
data() {
        return {
			ctx: null,
			canvasWidth: 1080,
			canvasHeight: 1440,
        }
    },

wx.draw(false, () =>{
  wx.canvasToTempFilePath({
       x: 0,
       y: 0,
       canvasId: 'shareCanvas',  // shareCanvas 为制定 绘图canvas 的ID
       success: (res) => {
            this.storeImgPath = res.tempFilePath
            ....写入生成完成的逻辑
       },
      complete: (res) => {
           wx.hideLoading()
       }
  })
})

//万能代码，不能用你回来找我，能用可以双击点赞评论666	
console.log('正在绘制')
			this.ctx.draw(false,(()=> {
				setTimeout(() => {
				uni.canvasToTempFilePath({
					x: 0,
					y: 0,
					width: this.canvasWidth1,
					height: this.canvasHeight1,
					destWidth: this.canvasWidth1,
					destHeight: this.canvasHeight1,
					canvasId: 'myCanvas',quality:0.6,
					success: res => {
						// 在H5平台下，tempFilePath 为 base64
						console.log(res,'绘制完成===',)
						//上传
						uni.uploadFile({
							url: url, //仅为示例，非真实的接口地址
							filePath:res.tempFilePath,
							header: {
								'token': self.$store.state.token,"version":"100.0.00"
							},
							name: 'file',
							formData: {},
							success: (uploadFileRes) => {
								console.log('uploadFileRes===1111',uploadFileRes)
								uni.hideLoading()
							},
							fail(err) {
								console.log(err)
								uni.hideLoading()
							}
						});
					//	this.pictureArr.push(res.tempFilePath);
					},
					fail(err) {
						console.log(err)
						uni.showToast({
							title:'上传图片失败!',icon:'none',
							duration: 3000
						})
						uni.hideLoading()
					}
				}, this)
				}, 3500)
			})());