// 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 = [
  'images/graphics/hm_honesty.gif',
  'images/graphics/hm_communication.gif',
  'images/graphics/hm_guidance.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);
  }
};