// IE5.5+ PNG Alpha Fix v2.0 Alpha: Background Tiling Support
// (c) 2008-2009 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 = Math.max(0, xPos + pngW > elmW ? elmW - xPos : pngW),
          clipB = Math.max(0, yPos + pngH > elmH ? elmH - yPos : pngH);
        d = tiles.cache[count];
        s = d.style;
        s.behavior = 'none';
        s.left = (xPos - parseInt(elm.currentStyle.paddingLeft)) + '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);
  });
}