利用canvas进行图片旋转

1.先放上需要旋转的图片和旋转按钮

旋转

注：@click="rotate('img', 'right')" 传需要旋转图片的id和需要旋转的方向； :src="imgPath" 绑定显示的图片

2.点击旋转按钮后执行的方法

rotate(pid, direction) {
    //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;
    var img = document.getElementById(pid);
    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  
    let height =  document.getElementById('image').height;
    let width = document.getElementById('image').width;
    console.log(height)
    console.log(width)
    var step = img.getAttribute('step');
    if(step == null) {
        step = min_step;
    }
    if(direction == 'right') {
                //向右转
        step++;
        //旋转到原位置，即超过最大值  
        step > max_step && (step = min_step);
    } else {
                //向左转
        step--;
        step < min_step && (step = max_step);
    }
    img.setAttribute('step', step);
    var canvas = document.getElementById('pic_' + pid);
    if(canvas == null) {
        img.style.display = 'none';
        canvas = document.createElement('canvas');
        canvas.setAttribute('id', 'pic_' + pid);
        img.parentNode.appendChild(canvas);
    }
    //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(step)
    switch(step) {
        case 0:
            canvas.width = width;
            canvas.height = height;
            ctx.drawImage(img, 0, 0, width, height);
            break;
            case 1:
            canvas.width = height;
            canvas.height = width;
            ctx.rotate(degree);
            ctx.drawImage(img, 0, -height, width, height, );
            break;
        case 2:
            canvas.width = width;
            canvas.height = height;
            ctx.rotate(degree);
            ctx.drawImage(img, 0, 0, -width, -height);
            break;
        case 3:
            canvas.width = height;
            canvas.height = width;
            ctx.rotate(degree);
            ctx.drawImage(img, -width, 0, width, height);
            break;
    }
        //将图片转为base64
    var ss = canvas.toDataURL(0.92);
        //将base64转为文件
        this.dataURL = this.dataURLtoFile(ss);
},

3.将base64转为文件的方法：

dataURLtoFile(dataurl, filename = 'file') {
        let arr = dataurl.split(',')
        let mime = arr[0].match(/:(.*?);/)[1]
        console.log(mime)
        let suffix = mime.split('/')[1]
        let bstr = atob(arr[1])
        let n = bstr.length
        let u8arr = new Uint8Array(n)
        while (n--) {
             u8arr[n] = bstr.charCodeAt(n)
        }
        return new File([u8arr], `${filename}.${suffix}`, {
             type: mime
        })
},

OK，就这样，End~