//----------------------------------
//
//**
// *
// * @authors liwb (lwbhtml@163.com)
// * @date    2019/3/12 15:22
// * @version $
// * @desc webp 的 CSS 背景兼容方案 retina兼容图片流量优化
// */
//----------------------------------

.retinabg(@file-2x; @reg-2x; @reg-1x; @type) when (isstring(@reg-2x)) {

  background-image: url("@{file-2x}.@{reg-1x}.@{type}");
  .webpa & {
    background-image: url('@{file-2x}.@{reg-1x}.@{type}.webp');
  }
  @media
  only screen and (-webkit-min-device-pixel-ratio: 2),
  only screen and (   min--moz-device-pixel-ratio: 2),
  only screen and (     -o-min-device-pixel-ratio: 2/1),
  only screen and (        min-device-pixel-ratio: 2),
  only screen and (                min-resolution: 192dpi),
  only screen and (                min-resolution: 2dppx) {
    background-image: url("@{file-2x}.@{reg-2x}.@{type}");
    .webpa & {
      background-image: url('@{file-2x}.@{reg-2x}.@{type}.webp');
    }
  }
}

// 使用方式
// .retinabg(http://cdn1.showjoy.com/images/bb/bb1c8b0d275e4ba2903dc822a03add50.png; 300x300; 150x150; png)