// isf31.11 :: Image swap-fade 
// *****************************************************
// DOM scripting by brothercake -- http://www.brothercake.com/
//******************************************************
//global object
var isf3 = { 'clock' : null, 'fade' : true, 'count' : 1 }
/*******************************************************



/*****************************************************************************
 List the images that need to be cached
*****************************************************************************/

isf3.imgs = [
	'buttons/udm4-whitebutton88x31.gif',
	'buttons/udm4-greenbutton88x31.gif',
	'buttons/udm4-purplebutton88x31.gif'
	];

/*****************************************************************************
*****************************************************************************/



//cache the images
isf3.imgsLen = isf3.imgs.length;
isf3.cache = [];
for(var i=0; i<isf3.imgsLen; i++)
{
	isf3.cache[i] = new Image;
	isf3.cache[i].src = isf3.imgs[i];
}


//swapfade3 setup function
function swapfade3()
{
	//if the timer is not already going
	if(isf3.clock == null)
	{
		//copy the image object 
		isf3.obj = arguments[0];
		
		//copy the image src argument 
		isf3.src = arguments[1];
		
		//store the supported form of opacity
		if(typeof isf3.obj.style.opacity != 'undefined')
		{
			isf3.type = 'w3c';
		}
		else if(typeof isf3.obj.style.MozOpacity != 'undefined')
		{
			isf3.type = 'moz';
		}
		else if(typeof isf3.obj.style.KhtmlOpacity != 'undefined')
		{
			isf3.type = 'khtml';
		}
		else if(typeof isf3.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
			isf3.type = (isf3.obj.filters.length > 0 && typeof isf3.obj.filters.alpha == 'object' && typeof isf3.obj.filters.alpha.opacity == 'number') ? 'ie' : 'none';
		}
		else
		{
			isf3.type = 'none';
		}
		
		//change the image alt text if defined
		if(typeof arguments[3] != 'undefined' && arguments[3] != '')
		{
			isf3.obj.alt = arguments[3];
		}
		
		//if any kind of opacity is supported
		if(isf3.type != 'none')
		{
			//copy and convert fade duration argument 
			//the duration specifies the whole transition
			//but the swapfade3 is two distinct transitions
			isf3.length = parseInt(arguments[2], 10) * 500;
			
			//create fade resolution argument as 20 steps per transition
			//again, split for the two distrinct transitions
			isf3.resolution = parseInt(arguments[2], 10) * 10;
			
			//start the timer
			isf3.clock = setInterval('isf3.swapfade3()', isf3.length/isf3.resolution);
		}
		
		//otherwise if opacity is not supported
		else
		{
			//just do the image swap
			isf3.obj.src = isf3.src;
		}
		
	}
};


//swapfade3 timer function
isf3.swapfade3 = function()
{
	//increase or reduce the counter on an exponential scale
	isf3.count = (isf3.fade) ? isf3.count * 0.9 : (isf3.count * (1/0.9)); 
	
	//if the counter has reached the bottom
	if(isf3.count < (1 / isf3.resolution))
	{
		//clear the timer
		clearInterval(isf3.clock);
		isf3.clock = null;

		//do the image swap
		isf3.obj.src = isf3.src;

		//reverse the fade direction flag
		isf3.fade = false;
		
		//restart the timer
		isf3.clock = setInterval('isf3.swapfade3()', isf3.length/isf3.resolution);

	}
	
	//if the counter has reached the top
	if(isf3.count > (1 - (1 / isf3.resolution)))
	{
		//clear the timer
		clearInterval(isf3.clock);
		isf3.clock = null;

		//reset the fade direction flag
		isf3.fade = true;
		
		//reset the counter
		isf3.count = 1;
	}

	//set new opacity value on element
	//using whatever method is supported
	switch(isf3.type)
	{
		case 'ie' :
			isf3.obj.filters.alpha.opacity = isf3.count * 100;
			break;
			
		case 'khtml' :
			isf3.obj.style.KhtmlOpacity = isf3.count;
			break;
			
		case 'moz' : 
			//restrict max opacity to prevent a visual popping effect in firefox
			isf3.obj.style.MozOpacity = (isf3.count == 1 ? 0.9999999 : isf3.count);
			break;
			
		default : 
			//restrict max opacity to prevent a visual popping effect in firefox
			isf3.obj.style.opacity = (isf3.count == 1 ? 0.9999999 : isf3.count);
	}
};