wx.canvasToTempFilePath，

发布的版本安卓手机使用没有任何问题，生成了我们要的带水印的图片。但是苹果手机生成的是空白的图片。

我们尝试了，加计时器，缩小图片大小。都不好使。

wx.canvasToTempFilePath({

                            canvas,

                            success: (res) => {

                                wx.saveImageToPhotosAlbum({

                                    filePath: res.tempFilePath,

                                    success: (res) => {

                                        wx.showToast({

                                            title: '保存成功',

                                            icon: 'success',

                                            duration: 2000

                                        })

                                    },

                                    fail: (res) => {

                                        wx.showToast({

                                            title: '保存失败',

                                            icon: 'error',

                                            duration: 2000

                                        })

                                    }

                                })

})