手机不定大小头像处理

图像尺寸可能有以下几种可能：宽>高，宽<高，宽=高

要求：最小的 宽/高 撑满盒子

<h2>1. CSS3 background实现</h2>
<div class="m-box box-background box-background-w"></div>
<div class="m-box box-background box-background-h"></div>
<div class="m-box box-background box-background-wh"></div>

/* 假设你已经拥有DEMO里需要的图片 */
.m-box {
    width: 100px; height: 100px;
    border-radius: 50%;
    overflow: hidden;
    margin-bottom: 20px;
}

.box-background-w { background-image: url(img/400x200.jpg); }
.box-background-h { background-image: url(img/200x400.jpg); }
.box-background-wh { background-image: url(img/400x400.jpg); }
.box-background {
    -webkit-background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}

<!-- 假设你已经拥有DEMO里需要的图片 -->
<h2>2. JS实现</h2>
<div class="m-box"><img class="J_CropImage" src="img/400x200.jpg" alt=""/></div>
<div class="m-box"><img class="J_CropImage" src="img/200x400.jpg" alt=""/></div>
<div class="m-box"><img class="J_CropImage" src="img/400x400.jpg" alt=""/></div>

<canvas id="canvas" width="100" height="100"></canvas>
<div id="after"></div>

.m-box {
    width: 100px; height: 100px;
    border-radius: 50%;
    overflow: hidden;
    margin-bottom: 20px;
}

#after { padding: 10px; }
#after img { margin: 10px; }

// use
var aImg = document.getElementsByClassName(‘J_CropImage‘);
for(var len = aImg.length - 1; len >= 0; len--){
    loadImg(aImg[len], aImg[len].getAttribute(‘src‘));
}

function getById(id){
    return document.getElementById(id);
}

// 加载图片
function loadImg(obj, src){
    var img = new Image();
    img.src = src;
    img.onload = function(){
        setImg(obj, img);
    };
}

// 设置图片位置
function setImg(o, img){
    var width = img.width, height = img.height,
            sx = 0, sy = 0, sw = 0, sh = 0, x = 0, y = 0, w = 100, h = 100;
    if(width > height){
        // 设置高度100%，改变宽度
        o.style.cssText = ‘height: 100%; margin-left: 50%; -webkit-transform: translateX(-50%); transform: translateX(-50%);‘;

        sx = (width - height)/2;
        sh = sw = height;
    }
    else if(height > width){
        // 设置宽度100%，改变高度
        o.style.cssText = ‘width: 100%; margin-top: 50%; -webkit-transform: translateY(-50%); transform: translateY(-50%);‘;

        sy = (height - width)/2;
        sh = sw = width;
    }
    else{
        // 相等，设置宽高100%
        o.style.cssText = ‘width: 100%; height: 100%;‘;
        sh = sw = height;
    }

    cropImage(img.src, sx, sy, sw, sh, x, y, w, h);
}

// 图片裁切
function cropImage(src, sx, sy, sw, sh, x, y, w, h){
    var oCanvas = getById(‘canvas‘);
    if(!oCanvas.getContext) return;

    var ctx = oCanvas.getContext(‘2d‘);
    var oImg = new Image();
    oImg.src = src;
    oImg.onload = function(){
        ctx.drawImage(oImg,
                sx, sy, sw, sh,
                x, y, w, h
        );

        var resImg = document.createElement(‘img‘);
        resImg.src = oCanvas.toDataURL(‘+image/png+‘, 0.8);
        getById(‘after‘).appendChild(resImg);
    };
}