// ISF1.11 :: Image swap-fade 
// *****************************************************
// DOM scripting by brothercake -- http://www.brothercake.com/
//******************************************************
//global object
var isf = { 'clock' : null, 'fade' : true, 'count' : 1 }
/*******************************************************
/*****************************************************************************
List the images that need to be cached
*****************************************************************************/
isf.imgs = [
'buttons/udm4-whitebutton88x31.gif',
'buttons/udm4-greenbutton88x31.gif',
'buttons/udm4-purplebutton88x31.gif'
];
/*****************************************************************************
*****************************************************************************/
//cache the images
isf.imgsLen = isf.imgs.length;
isf.cache = [];
for(var i=0; i<isf.imgsLen; i++)
{
isf.cache[i] = new Image;
isf.cache[i].src = isf.imgs[i];
}
//swapfade setup function
function swapfade()
{
//if the timer is not already going
if(isf.clock == null)
{
//copy the image object 
isf.obj = arguments[0];
//copy the image src argument 
isf.src = arguments[1];
//store the supported form of opacity
if(typeof isf.obj.style.opacity != 'undefined')
{
isf.type = 'w3c';
}
else if(typeof isf.obj.style.MozOpacity != 'undefined')
{
isf.type = 'moz';
}
else if(typeof isf.obj.style.KhtmlOpacity != 'undefined')
{
isf.type = 'khtml';
}
else if(typeof isf.obj.filters == 'object')
{
//weed out win/ie5.0 by testing the length of the filters collection (where filters is an object with no data)
//then weed out mac/ie5 by testing first the existence of the alpha object (to prevent errors in win/ie5.0)
//then the returned value type, which should be a number, but in mac/ie5 is an empty string
isf.type = (isf.obj.filters.length > 0 && typeof isf.obj.filters.alpha == 'object' && typeof isf.obj.filters.alpha.opacity == 'number') ? 'ie' : 'none';
}
else
{
isf.type = 'none';
}
//change the image alt text if defined
if(typeof arguments[3] != 'undefined' && arguments[3] != '')
{
isf.obj.alt = arguments[3];
}
//if any kind of opacity is supported
if(isf.type != 'none')
{
//copy and convert fade duration argument 
//the duration specifies the whole transition
//but the swapfade is two distinct transitions
isf.length = parseInt(arguments[2], 10) * 500;
//create fade resolution argument as 20 steps per transition
//again, split for the two distrinct transitions
isf.resolution = parseInt(arguments[2], 10) * 10;
//start the timer
isf.clock = setInterval('isf.swapfade()', isf.length/isf.resolution);
}
//otherwise if opacity is not supported
else
{
//just do the image swap
isf.obj.src = isf.src;
}
}
};
//swapfade timer function
isf.swapfade = function()
{
//increase or reduce the counter on an exponential scale
isf.count = (isf.fade) ? isf.count * 0.9 : (isf.count * (1/0.9)); 
//if the counter has reached the bottom
if(isf.count < (1 / isf.resolution))
{
//clear the timer
clearInterval(isf.clock);
isf.clock = null;
//do the image swap
isf.obj.src = isf.src;
//reverse the fade direction flag
isf.fade = false;
//restart the timer
isf.clock = setInterval('isf.swapfade()', isf.length/isf.resolution);
}
//if the counter has reached the top
if(isf.count > (1 - (1 / isf.resolution)))
{
//clear the timer
clearInterval(isf.clock);
isf.clock = null;
//reset the fade direction flag
isf.fade = true;
//reset the counter
isf.count = 1;
}
//set new opacity value on element
//using whatever method is supported
switch(isf.type)
{
case 'ie' :
isf.obj.filters.alpha.opacity = isf.count * 100;
break;
case 'khtml' :
isf.obj.style.KhtmlOpacity = isf.count;
break;
case 'moz' : 
//restrict max opacity to prevent a visual popping effect in firefox
isf.obj.style.MozOpacity = (isf.count == 1 ? 0.9999999 : isf.count);
break;
default : 
//restrict max opacity to prevent a visual popping effect in firefox
isf.obj.style.opacity = (isf.count == 1 ? 0.9999999 : isf.count);
}
};