ctx.draw(false, function() {

        console.log(w, h, "canvasToTempFilePath")
        setTimeout(function () {
          wx.canvasToTempFilePath({
            width: w,
            height: h,
            fileType: 'jpg',
            canvasId: `bgcavas${bgId}`,
            success: function (res) {
              wx.getImageInfo({
                src: res.tempFilePath,
                success: info => {
                  console.log(info, "info")
                }
              })
              that.setData({
                bgImg: res.tempFilePath
              });
            },
            complete: res => {
              if (res.errMsg == 'canvasToTempFilePath:ok') {
                that.setData({
                  bgImg: res.tempFilePath
                })
              } else {
                console.error('cavas 绘制图片错误')
              }
            }
          }, that)
        }, 3000)
      }); //开始绘制

这是cavas绘制的图片

使用api保存后的图片