// ISF1.11 :: Image swap-fade 
// *****************************************************
// DOM scripting by brothercake -- http://www.brothercake.com/
//******************************************************

var slideshow;  // setTimeout variable

function startSlideShow()   {
    //do the intial image swap
    swapfade(document.getElementById('slide_image'),'','2','Alt Text');

    //do the subsequent image swaps
    clearInterval(slideshow);
    slideshow = setInterval("swapfade(document.getElementById('slide_image'),'','2','Alt Text')",9000);
}

var kount = -1;

//global object
var isf = { 
    'clock' : null,
    'fade' : true,
    'count' : 1
}

//List the images that need to be cached
isf.imgs = [
    './pics/reception.jpg',
    './pics/home_slide_2.jpg',
    './pics/home_slide_1.jpg'
    ];

//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(ss_container,junk, speed, altText)
{
    //if the timer is not already going
    if(isf.clock == null)
    {
        //copy the image object
        isf.obj = ss_container;       
        
        //increment the image counter
        kount = kount + 1;
        if(kount > isf.imgsLen-1) kount = 0; 	
        
        //copy the image src argument
        isf.src = isf.cache[kount].src;
		
        //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

            if(isf.obj.filters.length > 0
                && typeof isf.obj.filters.alpha == 'object'
                && typeof isf.obj.filters.alpha.opacity == 'number') {
                isf.type = 'ie';
            }
            else {
                isf.type = 'none';
            }          
        }
        else
        {
            isf.type = 'none';
        }
		
        //change the image alt text if defined
        if(typeof altText != 'undefined' && altText != '')
        {
            isf.obj.alt = altText;
        }
		
        //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(speed, 10) * 500;
            
            //create fade resolution argument as 20 steps per transition
            //again, split for the two distrinct transitions
            isf.resolution = parseInt(speed, 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);
    }
};