// Centrado de capa en navegador

function centrar(capa, ancho, margen_top)
{

if(is.ns6) {
page_width=innerWidth;
page_height=innerHeight;
layerSetup(capa, ancho, margen_top);
} else if(is.ie5 || is.ie55 ||is.ie6) {
page_width=document.body.clientWidth;
page_height=document.body.clientHeight;
layerSetup(capa, ancho, margen_top);
}
}

function Is() {
    agent  = navigator.userAgent.toLowerCase();
    this.major = parseInt(navigator.appVersion);
    this.minor = parseFloat(navigator.appVersion);
    this.ns    = ((agent.indexOf('mozilla')   !=   -1) && ((agent.indexOf('spoofer')   ==   -1) && (agent.indexOf('compatible') ==   -1)));
    this.ns4   = (this.ns && (this.major      ==    4));
    this.ns6   = (this.ns && (this.major      >=    5));
    this.ie    = (agent.indexOf("msie")       !=   -1);
    this.ie3   = (this.ie && (this.major      < 4));
    this.ie4   = (this.ie && (this.major      ==    4) && (agent.indexOf("msie 5.0")   ==   -1));
    this.ie5   = (this.ie && (this.major      ==    4) && (agent.indexOf("msie 5.0")   !=   -1));
    this.ie55  = (this.ie && (this.major      ==    4) && (agent.indexOf("msie 5.5")   !=   -1));
    this.ie6  = (this.ie && (agent.indexOf("msie 6.0")!=-1) );
}

var is = new Is();

function layerObject(id,position,left,top,visibility) {
if (is.ie5|| is.ie55||is.ie6|| is.ns6){
this.obj = document.getElementById(id).style;
this.obj.position = position;
this.obj.left = left;
this.obj.top = top;
this.obj.visibility = visibility;
return this.obj;
}
}
function layerSetup(capa, ancho, margen_top)
{
	//page_height=page_height/2-alto/2;		// para centrar verticalmente habria que recibir tambien el alto
	page_height=margen_top;
	centerLyr = new layerObject(capa,'absolute', page_width/2-ancho/2,page_height,'visible');
}