/*                                                                                                         
 * Written by Stefano Mazzocchi <stefanom at mit.edu>                                                     
 * With code borrowed from http://www.splintered.co.uk/experiments/archives/javascript_fade/fade.js       
 */                                                                                                       
                                                                                                          
var delayInSeconds = 5;                                                                                   
                                                                                                          
var index;                                                                                                
var size;                                                                                                 
var items;                                                                                               
var keepGoing;                                                                                           
var opacity;                                                                                             
var displayedItem;                                                                                       
var itemToDisplay;                                                                                       
var idle = true;                                                                                         
                                                                                                         
addEvent(window,"load",slideshow);                                                                       
                                                                                                         
function slideshow() {                                                                                   
 items = getItems();                                                                                     
 size = items.length;                                                                                    
 index = Math.floor(Math.random() * (size - 1));                                                         
 start();                                                                                                
}                                                                                                        
                                                                                                         
function getItems() {                                                                                    
 var items = [];                                                                                         
 var divs = document.getElementById("slideshow").getElementsByTagName("div");                            
 for (var i = 0; i < divs.length; i++) {                                                                 
 if (divs[i].className == "item") items.push(divs[i]);                                                   
 }                                                                                                       
 return items;                                                                                           
}                                                                                                        
                                                                                                         
function start() {                                                                                       
 document.getElementById("stop").style.display = "inline";                                               
 document.getElementById("start").style.display = "none";                                                
 document.getElementById("previous").style.display = "none";                                             
 document.getElementById("next").style.display = "none";                                                 
 keepGoing = true;                                                                                       
 beat();                                                                                                 
}                                                                                                        
                                                                                                         
function stop() {                                                                                        
 document.getElementById("stop").style.display = "none";                                                 
 document.getElementById("start").style.display = "inline";                                              
 document.getElementById("previous").style.display = "inline";                                           
 document.getElementById("next").style.display = "inline";                                               
 keepGoing = false;                                                                                      
}                                                                                                        
                                                                                                         
function beat() {                                                                                        
 if (keepGoing) {                                                                                        
 next();                                                                                                 
 window.setTimeout("beat()", 1000 * delayInSeconds);                                                     
 }                                                                                                       
}                                                                                                        
                                                                                                         
function next() {                                                                                        
 if (index < size - 1) {                                                                                 
 show1(index + 1);                                                                                       
 } else {                                                                                                
 show1(0);                                                                                               
 }                                                                                                       
}                                                                                                        
                                                                                                         
function previous() {                                                                                    
 if (index > 0) {                                                                                        
 show1(index - 1);                                                                                       
 } else {                                                                                                
 show1(size - 1);                                                                                        
 }                                                                                                       
}                                                                                                        
                                                                                                         
function show1(newIndex) {                                                                               
 if (idle) {                                                                                             
 idle = false;                                                                                           
 index = newIndex;                                                                                       
 goOn = show2;                                                                                           
 if (displayedItem) {                                                                                    
 opacity = 100;                                                                                          
 fadeOut(); // this will call goOn() when done fading                                                    
 } else {                                                                                                
 goOn();                                                                                                 
 }                                                                                                       
 }                                                                                                       
}                                                                                                        
                                                                                                         
function show2() {                                                                                       
 goOn = show3;                                                                                           
 opacity = 0;                                                                                            
 itemToDisplay = items[index];                                                                           
 setOpacity(itemToDisplay, opacity);                                                                     
 itemToDisplay.style.display = "block";                                                                  
 fadeIn(); // this will call goOn() when done fading                                                     
}                                                                                                        
                                                                                                         
function show3() {                                                                                       
 displayedItem = itemToDisplay; // this is the end of our item showing routine                           
 idle = true;                                                                                           
}                                                                                                       
                                                                                                        
function fadeIn() {                                                                                     
 opacity += 10;                                                                                         
 if (opacity <= 100 && !document.all) {                                                                 
 setOpacity(itemToDisplay, opacity);                                                                    
 window.setTimeout("fadeIn()", 50);                                                                     
 } else {                                                                                               
 if (goOn) goOn();                                                                                      
 }                                                                                                      
}                                                                                                       
                                                                                                        
function fadeOut() {                                                                                    
 opacity -= 10;                                                                                         
 if (opacity >= 0 && !document.all) {                                                                   
 setOpacity(displayedItem, opacity);                                                                    
 window.setTimeout("fadeOut()", 50);                                                                    
 } else {                                                                                               
 displayedItem.style.display = "none";                                                                  
 if (goOn) goOn();                                                                                      
 }                                                                                                      
}                                                                                                       
                                                                                                        
function setOpacity(target, opacity) {                                                                  
 if (target && opacity <= 100) {                                                                        
 if (target.style.opacity != null) { // CSS3 compatible                                                 
 target.style.opacity = (opacity / 100) - 0.001;                                                        
 } else if (target.style.MozOpacity != null) { // Mozilla's pre-CSS3 proprietary rule                   
 target.style.MozOpacity = (opacity / 100) - 0.001;                                                     
 // the .001 fixes a glitch in the opacity calculation which normally results in a flash when reaching 1
 }                                                                                                      
 // yes, I know that even IE has a proprietary opacity filter, but unfortunately                        
 // it works fine on images, but screws up text rendering completely, so I'm not using it.              
 }                                                                                                      
}                                                                                                       
                                                                                                        
function addEvent(elm, evType, fn, useCapture) {                                                        
 if (elm.addEventListener){                                                                             
 elm.addEventListener(evType, fn, useCapture);                                                          
 return true;                                                                                           
 } else if (elm.attachEvent){                                                                           
 var r = elm.attachEvent("on"+evType, fn);                                                              
 return r;                                                                                              
 }                                                                                                      
}