吐槽：某厂的开发文档写的跟屎一样

1、后台返回accessToken，小程序请求获取小程序码

uni.request({
                        url: 'https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=' + res.data
                            .accessToken,
                        method: 'POST',
                        headers: {
                            'Content-Type': 'json'
                        },
                        responseType: 'arraybuffer',
                        data: {                         
                            "scene": "a=1", // 参数
                            "is_hyaline": true //透明底色
                        },
                        success: (res) => {
                            // 将返回的图片buffer生成图片，并保存至临时用户文件中
                            const fs = wx.getFileSystemManager();
                            const FILE_BASE_NAME = 'code';
                            let filePath = `${wx.env.USER_DATA_PATH}/${FILE_BASE_NAME}.png`;
                            fs.writeFileSync(filePath, res.data)
                            // filePath就是图片的本地路径
                            that.filePath = filePath
                            that.qrcode(filePath)
                        },
                        fail(e) {
                            console.log(e)
                        }
                    });

2、将生成的小程序码绘制到海报上 --- canvas

let that = this
                const query = wx.createSelectorQuery()
                query.select('#myCanvas')
                    .fields({
                        node: true,
                        size: true
                    })
                    .exec((res) => {
                        
                        const canvas = res[0].node
                        const ctx = canvas.getContext('2d')

                        const headerImg = canvas.createImage();
                        const backImg = canvas.createImage();

                        headerImg.src = that.filePath;
                        backImg.src = '../../static/wish.png';

                                                backImg.onload = () => {
                            ctx.drawImage(backImg, 0, 0, 150, 100)
                        }   

                        headerImg.onload = () => {
                            ctx.drawImage(headerImg, 0, 0, 150, 100)
                        }
                                            
                    })
                

3、将生成的小程序码绘制到海报上 --- canvas离屏绘制

// 创建离屏 2D canvas 实例
                const canvas = wx.createOffscreenCanvas({
                    type: '2d',
                    width: 300,
                    height: 150
                })
                // 获取 context。注意这里必须要与创建时的 type 一致
                const context = canvas.getContext('2d')
                // 创建一个图片
                const image = canvas.createImage()
                // 等待图片加载

                image.src = '../../static/wish.png' // 要加载的图片 url
                image.onload = () => {
                    // 把图片画到离屏 canvas 上
                    context.clearRect(0, 0, 300, 150)
                    context.drawImage(image, 0, 0, 300, 150)

                    // 获取画完后的数据
                    const imgData = context.getImageData(0, 0, 300, 150)
                    console.log(imgData)
                                        // 图片的base64格式
                    console.log(context.canvas.toDataURL())
                    that.src = context.canvas.toDataURL()
                }