移動端Retina屏幕圖片適配

第一個方法

;(function(win, lib) {
    var doc = win.document;
    var docEl = doc.documentElement;
    var metaEl = doc.querySelector('meta[name="viewport"]');
    var flexibleEl = doc.querySelector('meta[name="flexible"]');
    var dpr = 0;
    var scale = 0;
    var tid;
    var flexible = lib.flexible || (lib.flexible = {});

    if (metaEl) {
        console.warn('將根據已有的meta標籤來設置縮放比例');
        var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
        if (match) {
            scale = parseFloat(match[1]);
            dpr = parseInt(1 / scale);
        }
    } else if (flexibleEl) {
        var content = flexibleEl.getAttribute('content');
        if (content) {
            var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
            var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
            if (initialDpr) {
                dpr = parseFloat(initialDpr[1]);
                scale = parseFloat((1 / dpr).toFixed(2));    
            }
            if (maximumDpr) {
                dpr = parseFloat(maximumDpr[1]);
                scale = parseFloat((1 / dpr).toFixed(2));    
            }
        }
    }

    if (!dpr && !scale) {
        var isAndroid = win.navigator.appVersion.match(/android/gi);
        var isIPhone = win.navigator.appVersion.match(/iphone/gi);
        var devicePixelRatio = win.devicePixelRatio;
        if (isIPhone) {
            // iOS下,對於2和3的屏,用2倍的方案,其餘的用1倍方案
            if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {                
                dpr = 3;
            } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){
                dpr = 2;
            } else {
                dpr = 1;
            }
        } else {
            // 其他設備下,仍舊使用1倍的方案
            dpr = 1;
        }
        scale = 1 / dpr;
    }

    docEl.setAttribute('data-dpr', dpr);
    if (!metaEl) {
        metaEl = doc.createElement('meta');
        metaEl.setAttribute('name', 'viewport');
        metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
        if (docEl.firstElementChild) {
            docEl.firstElementChild.appendChild(metaEl);
        } else {
            var wrap = doc.createElement('div');
            wrap.appendChild(metaEl);
            doc.write(wrap.innerHTML);
        }
    }

    function refreshRem(){
        var width = docEl.getBoundingClientRect().width;
        if (width / dpr > 540) {
            width = 540 * dpr;
        }
        var rem = width / 10;
        docEl.style.fontSize = rem + 'px';
        flexible.rem = win.rem = rem;
    }

    win.addEventListener('resize', function() {
        clearTimeout(tid);
        tid = setTimeout(refreshRem, 300);
    }, false);
    win.addEventListener('pageshow', function(e) {
        if (e.persisted) {
            clearTimeout(tid);
            tid = setTimeout(refreshRem, 300);
        }
    }, false);

    if (doc.readyState === 'complete') {
        doc.body.style.fontSize = 12 * dpr + 'px';
    } else {
        doc.addEventListener('DOMContentLoaded', function(e) {
            doc.body.style.fontSize = 12 * dpr + 'px';
        }, false);
    }


    refreshRem();

    flexible.dpr = win.dpr = dpr;
    flexible.refreshRem = refreshRem;
    flexible.rem2px = function(d) {
        var val = parseFloat(d) * this.rem;
        if (typeof d === 'string' && d.match(/rem$/)) {
            val += 'px';
        }
        return val;
    }
    flexible.px2rem = function(d) {
        var val = parseFloat(d) / this.rem;
        if (typeof d === 'string' && d.match(/px$/)) {
            val += 'rem';
        }
        return val;
    }

})(window, window['lib'] || (window['lib'] = {}));

meta標籤

<meta>標籤有很多種,而這裏要着重說的是viewportmeta標籤,其主要用來告訴瀏覽器如何規範的渲染Web頁面,而你則需要告訴它視窗有多大。在開發移動端頁面,我們需要設置meta標籤如下:

<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">//如果你確定要用這個js請屏蔽掉,該js會自動創建

js會在html標籤內創建這個:

<html data-dpr="2" style="font-size: 64px;">

現在樣式寫法

.test{background: url(img/m3-phone.32.png) no-repeat; background-size:122px 247px; width: 122px; height: 247px;}
[data-dpr="2"] .test {
    background: url(img/m3-phone.32@2x.png) no-repeat;
  }

這段js是來自淘寶移動端自適應方案,
詳細鏈接:http://www.cnblogs.com/lyzg/p/5058356.html
在github:https://github.com/amfe/lib-flexible

方法二:
第二個方法則是使用css的device-pixel-ratio具體的寫法如下:

.test1-r {
                background: url(img/m3-phone.32.png) no-repeat;
                background-size: 122px 247px;
                width: 122px;
                height: 247px;
            }
@media all and (-webkit-min-device-pixel-ratio: 1.5),
            all and (-o-min-device-pixel-ratio: 3 / 2),
            all and (min--moz-device-pixel-ratio: 1.5),
            all and (min-device-pixel-ratio: 1.5) {
                .test1-r {
                    background: url(img/m3-phone.32@2x.png) no-repeat;
                    background-size: 122px 247px;
                }
            }

            @media (-webkit-min-device-pixel-ratio: 2),
            (min-resolution: 192dpi) {
                .test1-r {
                    background: url(img/m3-phone.32@2x.png) no-repeat;
                    background-size: 122px 247px;
                }
            }

            @media (-webkit-min-device-pixel-ratio: 3),
            (min-resolution: 288dpi) {
                .test1-r {
                    background: url(img/m3-phone.32@3x.png) no-repeat;
                    background-size: 122px 247px;
                }
            }

方法三:
使用retina.js,具體的使用方法沒有研究

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