小程序 圖片轉base64然后上傳的坑點

圖片上傳要用到upng.js  

　　　　　　　　　　const self = this

                const ctx = wx.createCanvasContext('myCanvas')
                const platform = wx.getSystemInfoSync().platform
                const imgWidth = 60, imgHeight = 60;
                wx.chooseImage({
                    success: res => {
                        //生成的圖片臨時路徑畫成canvas
                        ctx.drawImage(res.tempFilePaths[0], 0, 0, imgWidth, imgHeight)
                        ctx.draw(false, () => {
                            self.drawFinish = true
                            wx.canvasGetImageData({
                                canvasId: 'myCanvas',
                                x: 0,
                                y: 0,
                                width: imgWidth,
                                height: imgHeight,
                                success: res => {
                                    if (platform === 'ios') {
                                        // 兼容處理：ios獲取的圖片上下顛倒
                                        res = this.reverseImgData(res)
                                    }
                                    // 3. png編碼
                                    let pngData = upng.encode([res.data.buffer], res.width, res.height)
                                    // 4. base64編碼

                                    let base64 = wx.arrayBufferToBase64(pngData)
                                    debugger
                                    console.log('data:image/jpeg;base64,' + base64)
                                    this.setData({
                                        avatarUrl: 'data:image/jpeg;base64,' + base64
                                    });
                                },
                                fail(res) {
                                    debugger
                                    console.log(res)
                                },
                            })
                        })
                    }
                })

這里要有幾個坑
1.canvas那個標簽如果隱藏，會出現轉base64失敗的情況
2.ios上圖片需要翻轉