视网膜屏 retina屏

/*默认*/
an{
    background-image:url(img@1x.png);
}
/*2*/
@media screen and (-webkit-min-device-pixel-ratio:2){
    background-image:url(img@2x.png);
}

/*2*/
@media screen and (-webkit-min-device-pixel-ratio:3){
    background-image:url(img@3x.png);
}

/*js*/
var pixelRadio = window.devicePixelRatio,
pics = ['image@' + pixelRadio + 'x.png'],
leng = pics.length;