var settings = {
	'ID_parent'  : 'main', // ID rodicovskeho objektu pro scrollovani
	'ID_btnUp'   : 'btnUp', // ID buttonku pro posun nahoru
	'ID_btnDown' : 'btnDown', // ID buttonku pro posun dolu
	'ID_picture' : 'main-fade', // ID obrazku, ktery na zacatku prekryva text
	'speed'      : 10, // rychlost scrollovani (pixels per 50 miliseconds)
	'delay'      : 0.5, // pocet sekund, za ktere zacne mizet puvodni obrazek
	'fade_out'   : 60 // milisekundy, za ktere zpruhledni puvodni obrazek o 5%
};

var global = {};

function move(p) { 
	if (global.prior <= p && global.nInterval == 0) {	
		global.prior = 0;
		global.nInterval = setInterval("adjust()", 50);
	}
};
function stop(p) { 
	if (global.prior < p) 
		global.prior = p;
	if (global.nInterval != 0) {
		clearInterval(global.nInterval)
		global.nInterval = 0
	}
};
function allowScrolling() {
	document.onkeydown = function(e){
		var e = e || window.event;
		switch(e.keyCode) {
			case 38:
				global.nStep = -global.nAstep; 
				move(1);
				break;
			case 40:
				global.nStep = global.nAstep; 
				move(1);
				break;		
		}
	}
	document.onkeyup = function(e){
		var e = e || window.event;
		switch(e.keyCode) {
			case 38:
			case 40:
				stop(1);
				break;		
		}
	}

	var btnUp = document.getElementById(settings.ID_btnUp);
	var btnDown = document.getElementById(settings.ID_btnDown);
	btnUp.onmouseover = function () { 
		global.nStep = -global.nAstep; 
		move(1);
	}
	btnDown.onmouseover = function () { 
		global.nStep = global.nAstep; 
		move(1);
	}
	btnUp.onmouseout = btnDown.onmouseout = function () { 
		global.nPos += global.nStep;
		stop(1);
	}
};

function fadeOut() {
	global.nFade -= 5;
	if (global.nFade <= 0) {
		global.oCover.parentNode.removeChild(global.oCover);
		clearInterval(global.nIntervalFade);
		allowScrolling();
		return;
	}
	global.oCover.style.filter = "alpha(opacity='" + global.nFade + "')"
	global.oCover.style['-moz-opacity'] = global.nFade / 100; 0.7;
	global.oCover.style.opacity = global.nFade / 100;
}

function init() {
	global.oParent = document.getElementById(settings.ID_parent);
	global.oCover = document.getElementById(settings.ID_picture);
	global.nStep = settings.speed;
	global.nAstep = Math.abs(global.nStep);
	global.nInterval = global.prior = 0;
	global.nFade = 100;
	if (global.oCover == null)
		allowScrolling();
	else
		setTimeout(function () {global.nIntervalFade = setInterval("fadeOut()", settings.fade_out);}, settings.delay * 1000);
};

function adjust () {
	global.oParent.scrollTop += global.nStep;
};