学步园

// IE5.5+ PNG Alpha Fix v2.0 Alpha: Background Tiling Support
// (c) 2008 Angus Turnbull http://www.twinhelix.com

// This is licensed under the GNU LGPL, version 2.1 or later.
// For details, see: http://creativecommons.org/licenses/LGPL/2.1/

var IEPNGFix = window.IEPNGFix || {};
IEPNGFix.tileBG = function(elm, pngSrc, ready) {
    // Params: A reference to a DOM element, the PNG src file pathname, and a
    // hidden "ready-to-run" passed when called back after image preloading.

    var data = this.data[elm.uniqueID],
        elmW = Math.max(elm.clientWidth, elm.scrollWidth),
        elmH = Math.max(elm.clientHeight, elm.scrollHeight),
        bgX = elm.currentStyle.backgroundPositionX,
        bgY = elm.currentStyle.backgroundPositionY,
        bgR = elm.currentStyle.backgroundRepeat;
    // Cache of DIVs created per element, and image preloader/data.
    if (!data.tiles) {
        data.tiles = {
            elm: elm,
            src: '',
            cache: [],
            img: new Image(),
            old: {}
        };
    }
    var tiles = data.tiles,
        pngW = tiles.img.width,
        pngH = tiles.img.height;
    if (pngSrc) {
        if (!ready && pngSrc != tiles.src) {
            // New image? Preload it with a callback to detect dimensions.
            tiles.img.onload = function() {
                this.onload = null;
                IEPNGFix.tileBG(elm, pngSrc, 1);
            };
            return tiles.img.src = pngSrc;
        }
    } else {
        // No image?
        if (tiles.src) ready = 1;
        pngW = pngH = 0;
    }
    tiles.src = pngSrc;
    if (!ready && elmW == tiles.old.w && elmH == tiles.old.h &&
        bgX == tiles.old.x && bgY == tiles.old.y && bgR == tiles.old.r) {
        return;
    }
    // Convert English and percentage positions to pixels.
    var pos = {
            top: '0%',
            left: '0%',
            center: '50%',
            bottom: '100%',
            right: '100%'
        },
        x,
        y,
        pc;
    x = pos[bgX] || bgX;
    y = pos[bgY] || bgY;
    if (pc = x.match(/(\d+)%/)) {
        x = Math.round((elmW - pngW) * (parseInt(pc[1]) / 100));
    }
    if (pc = y.match(/(\d+)%/)) {
        y = Math.round((elmH - pngH) * (parseInt(pc[1]) / 100));
    }
    x = parseInt(x);
    y = parseInt(y);
    // Handle backgroundRepeat.
    var repeatX = { 'repeat': 1, 'repeat-x': 1 }[bgR],
        repeatY = { 'repeat': 1, 'repeat-y': 1 }[bgR];
    if (repeatX) {
        x %= pngW;
        if (x > 0) x -= pngW;
    }
    if (repeatY) {
        y %= pngH;
        if (y > 0) y -= pngH;
    }
    // Go!
    this.hook.enabled = 0;
    if (!({ relative: 1, absolute: 1 }[elm.currentStyle.position])) {
        elm.style.position = 'relative';
    }
    var count = 0,
        xPos,
        maxX = repeatX ? elmW : x + 0.1,
        yPos,
        maxY = repeatY ? elmH : y + 0.1,
        d,
        s,
        isNew;
    if (pngW && pngH) {
        for (xPos = x; xPos < maxX; xPos += pngW) {
            for (yPos = y; yPos < maxY; yPos += pngH) {
                isNew = 0;
                if (!tiles.cache[count]) {
                    tiles.cache[count] = document.createElement('div');
                    isNew = 1;
                }
                var clipR = (xPos + pngW > elmW ? elmW - xPos : pngW),
                    clipB = (yPos + pngH > elmH ? elmH - yPos : pngH);
                d = tiles.cache[count];
                s = d.style;
                s.behavior = 'none';
                s.left = xPos + 'px';
                s.top = yPos + 'px';
                s.width = clipR + 'px';
                s.height = clipB + 'px';
                s.clip = 'rect(' +
                    (yPos < 0 ? 0 - yPos : 0) + 'px,' +
                    clipR + 'px,' +
                    clipB + 'px,' +
                    (xPos < 0 ? 0 - xPos : 0) + 'px)';
                s.display = 'block';
                if (isNew) {
                    s.position = 'absolute';
                    s.zIndex = -999;
                    if (elm.firstChild) {
                        elm.insertBefore(d, elm.firstChild);
                    } else {
                        elm.appendChild(d);
                    }
                }
                this.fix(d, pngSrc, 0);
                count++;
            }
        }
    }
    while (count < tiles.cache.length) {
        this.fix(tiles.cache[count], '', 0);
        tiles.cache[count++].style.display = 'none';
    }
    this.hook.enabled = 1;
    // Cache so updates are infrequent.
    tiles.old = {
        w: elmW,
        h: elmH,
        x: bgX,
        y: bgY,
        r: bgR
    };
};
IEPNGFix.update = function() {
    // Update all PNG backgrounds.
    for (var i in IEPNGFix.data) {
        var t = IEPNGFix.data[i].tiles;
        if (t && t.elm && t.src) {
            IEPNGFix.tileBG(t.elm, t.src);
        }
    }
};
IEPNGFix.update.timer = 0;
if (window.attachEvent && !window.opera) {
    window.attachEvent('onresize', function() {
        clearTimeout(IEPNGFix.update.timer);
        IEPNGFix.update.timer = setTimeout(IEPNGFix.update, 100);
    });
}