//------------------------------------------------------------------

//  sdss-main-scroll.js  - javascript for the SDSS scrolling display

//  written by Alex Szalay, Dec 30, 2000

//  it assumes mosaic files in the path

//------------------------------------------------------------------


  var p,next,status;

    

  function nextImg() {
	var s = getFileName(next);

	if (++next>FIELD_MAX)

		resetStripe();

	return s;
  }



  function move() {

    if (status)
		for (var i = 0; i < p.length; i++) {p[i].move();}
	timer = setTimeout("move()",DELTA_T);

  }

  

  function toggle() {

	status = !status;
  }


  //--------------- definition of the Scroll class --------

  
  function Scroll(i,step) {

	this.id   = i;

	this.step = step;
	this.pos  = i*STRIDE;

	this.setDiv();
	this.nextSrc();

	this.div.top = this.pos;

  } 

  

  Scroll.prototype.setDiv = function() {
	if (is.ns4) {this.div = document["s"+this.id];}

	else if (is.ns6) {this.div = document.getElementById("s"+this.id).style;}
	else if (is.ie) {this.div = document.all["s"+this.id].style;}
  }

  

  Scroll.prototype.move = function () {
	if (this.pos < -HEIGHT) {
		this.pos += p.length*STRIDE;

		this.nextSrc();

	}

	this.pos    -= this.step;
	this.div.top = this.pos;

  }

  

  Scroll.prototype.nextSrc = function() {

	if (is.ns4) {
		document["s"+this.id].document.images["img"+this.id].src = nextImg();
	} else if (is.ns6) {
		document.images["img"+this.id].src = nextImg();

	} else if (is.ie) {
		document.all["img"+this.id].src = nextImg();
	}

  }

  //-------------------------------------------------------


  

  function init(stepsize) {



	//initialize the state variables, and the array
	  

    status = false;
	next   = FIELD_MIN;



	p = new Array(3);

    for (var i = 0; i < p.length; i++) {

		p[i] = new Scroll(i,stepsize);

    }

	status = true;
	move();

  }



  function Is() {

	this.id    = navigator.appVersion;
	this.major = parseInt(navigator.appVersion);
	this.agent = navigator.userAgent.toLowerCase();
	this.ns = ( (this.agent.indexOf('mozilla')!=-1) &&

				(this.agent.indexOf('spoofer')==-1) &&

				(this.agent.indexOf('compatible')==-1) &&

				(this.agent.indexOf('opera')==-1));
	this.ns4 = (this.ns && (this.major==4));

	this.ns6 = (this.ns && (this.major>=5));
	this.ie  = (this.agent.indexOf('msie')!=-1);
  }