uniapp H5图片上传压缩自动旋转

//H5压终审图片上传  
const  upload= async (opt) => {  
    let maxWidth = 500; //压缩图片最大宽度  
    opt = opt || {};  
    opt.url = opt.url || '';  
    opt.success = opt.success || function(){ };  
    console.log(opt.url)  
    let Orientation = 1;  
    //获取图片META信息  
    await getImageTag(opt.url, 'Orientation', function(e) {  
        if(e != undefined) Orientation = e;  
    })  
    var img = null;  
    var canvas = null;  
    await comprossImage(opt.url, maxWidth, function(e) {  
        img = e.img;  
        canvas = e.canvas;  
    })  

    console.log(Orientation)  
    let baseStr = '';  
    //如果方向角不为1，都需要进行旋转  
    switch(Orientation){  
        case 6://需要顺时针（向右）90度旋转  
            console.log('（向右）90度旋转');  
            baseStr = rotateImg(img,'right',canvas);  
            break;  
        case 8://需要逆时针（向左）90度旋转  
            console.log('向左）90度旋转');  
            baseStr = rotateImg(img,'left',canvas);  
            break;  

        case 3://需要180度旋转 转两次  
            console.log('需要180度旋转');  
            baseStr = rotateImg(img,'right',canvas, 2);  
            break;  
        default:  
            baseStr = rotateImg(img,'',canvas);  
            break;  
    }  
       opt.success(baseStr);  //公共方法的回调函数  
}  

const comprossImage = async (imgSrc, maxWidth, func) => {  
    if(!imgSrc) return 0;  
    return new Promise((resolve, reject) => {  
        uni.getImageInfo({  
            src: imgSrc,  
            success(res) {  
                let img = new Image();  
                img.src = res.path;  
                console.log(img)  

                let canvas = document.createElement('canvas');  

                let obj = new Object();  
                obj.img = img;  
                obj.canvas = canvas;  
                resolve(func(obj));  
            }  
        });  
    })  
}  

/**  
 * @desc 获取图片信息，使用exif.js库，具体用法请在github中搜索  
 * @param {Object} file 上传的图片文件  
 * @param {String} tag 需要获取的信息 例如：'Orientation'旋转信息  
 * @return {Promise<Any>} 读取是个异步操作，返回指定的图片信息  
 */  
const getImageTag = (file, tag, suc) => {  
    if (!file) return 0;  
    return new Promise((resolve, reject) => {  
        /* eslint-disable func-names */  
        // 箭头函数会修改this，所以这里不能用箭头函数  
        let imgObj = new Image()  
        imgObj.src = file  
        console.log(imgObj)  
        uni.getImageInfo({  
            src: file,  
            success(res) {  
                Exif.getData(imgObj, function () {  
                    Exif.getAllTags(this);    
                    let or = Exif.getTag(this,'Orientation');//这个Orientation 就是我们判断需不需要旋转的值了，有1、3、6、8  
                    resolve(suc(or))  
                });  
            }  
        })  
    });  
};  

//网上提供的旋转function  
const rotateImg = (img, direction, canvas, times = 1) => {   
    console.log('开始旋转')  
    //最小与最大旋转方向，图片旋转4次后回到原方向    
    var min_step = 0;    
    var max_step = 3;    
    if (img == null)return;    

    //img的高度和宽度不能在img元素隐藏后获取，否则会出错    
    var height = img.height;    
    var width = img.width;    
    let maxWidth = 500;  
    let canvasWidth = width; //图片原始长宽  
    let canvasHeight = height;  
    let base = canvasWidth/canvasHeight;  
    console.log(maxWidth);  
    if(canvasWidth > maxWidth){  
        canvasWidth = maxWidth;  
        canvasHeight = Math.floor(canvasWidth/base);  
    }  
    width = canvasWidth;  
    height = canvasHeight;  
    var step = 0;    

    if (step == null) {    
      step = min_step;    
    }    

    if (direction == 'right') {    
      step += times;    
      //旋转到原位置，即超过最大值    
      step > max_step && (step = min_step);    
    } else if(direction == 'left'){    
      step -= times;    
      step < min_step && (step = max_step);    
    } else {    //不旋转  
        step = 0;  
    }  

    //旋转角度以弧度值为参数    
    var degree = step * 90 * Math.PI / 180;    
    var ctx = canvas.getContext('2d');    
    console.log(degree)  
    console.log(step)  
    switch (step) {      
      case 1:    
        console.log('右旋转 90度')  
        canvas.width = height;    
        canvas.height = width;    
        ctx.rotate(degree);    
        ctx.drawImage(img, 0, -height, width, height);    
        break;    
      case 2:    
        //console.log('旋转 180度')  
        canvas.width = width;    
        canvas.height = height;    
        ctx.rotate(degree);    
        ctx.drawImage(img, -width, -height, width, height);    
        break;    
      case 3:    
        console.log('左旋转 90度')  
        canvas.width = height;    
        canvas.height = width;    
        ctx.rotate(degree);    
        ctx.drawImage(img, -width, 0, width, height);  
        break;    
      default:  //不旋转  
        canvas.width = width;  
        canvas.height = height;  
        ctx.drawImage(img, 0, 0, width, height);  
        break;  
    }  

    let baseStr = canvas.toDataURL("image/jpeg", 1);  
    return baseStr;  
}