var CurrentID = 0;
var PrevID = 0;
var SLIDEDELAY = 3000;
function showNextProblem(){
	CurrentID++;
	
	
	if (PrevID!=0){ // Konqueror and Opera 8 and less do not support opacity
			if ((navigator.userAgent.indexOf('Opera')==-1)&&(navigator.userAgent.indexOf('Konq')==-1)) {
			opacity('problem'+PrevID,100,0,SLIDEDELAY);
			}
			else
			{
			document.getElementById('problem'+PrevID).style.display='none';	
			}
		}
	opacity('problem'+(CurrentID),0,100,SLIDEDELAY);
	PrevID=CurrentID;
	if (CurrentID==6){
		CurrentID =0;
	}
	
}	
function hideFirstProblem(){
		opacity('problem1',0,100,SLIDEDELAY);
}

function adjustProblemTops(topValue){
		//for (i=1;i<6;i++){
		//	document.getElementById('problem'+i).style.position='absolute';
		//	document.getElementById('problem'+i).style.top=topValue;
		//}
}

function initProblems(){
	if(navigator.appName == "Microsoft Internet Explorer"){
 			adjustProblemTops(35);}
 		else{
 			adjustProblemTops(120);	
	}
	for (i=1;i<6;i++){
			changeOpac(0,'problem'+i);
	}	
	hideFirstProblem();
	nextTimer();
}
function nextTimer(){
	
	showNextProblem();
	setTimeout("nextTimer()",SLIDEDELAY * 2);
	
}

function opacity(id, opacStart, opacEnd, millisec) {
    //speed for each frame
    var speed = Math.round(millisec / 100);
    var timer = 0;

    //determine the direction for the blending, if start and end are the same nothing happens
    if(opacStart > opacEnd) {
        for(i = opacStart; i >= opacEnd; i--) {
            setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
            timer++;
        }
		

    } else if(opacStart < opacEnd) {
    	document.getElementById(id).style.display='block';
        for(i = opacStart; i <= opacEnd; i++)
            {
            setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
            timer++;
        }
    }
}

//change the opacity for different browsers
function changeOpac(opacity, id) {
    var object = document.getElementById(id).style;
    object.opacity = (opacity / 100);
    object.MozOpacity = (opacity / 100);
    object.KhtmlOpacity = (opacity / 100);
    object.filter = "alpha(opacity=" + opacity + ")";
	if (opacity==0){
		document.getElementById(id).style.display='none';	
	}
	else
		{
			document.getElementById(id).style.display='block';
		}
    
    	
} 

function shiftOpacity(id, millisec) {
    //if an element is invisible, make it visible, else make it ivisible
    if(document.getElementById(id).style.opacity == 0) {
        opacity(id, 0, 100, millisec);
    } else {
        opacity(id, 100, 0, millisec);
    }
}