// 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);
    }
};