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) {
		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 + ")";
}

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);
	}
}

function blendimage(divid, imageid, imagefile, millisec) {
	var speed = Math.round(millisec / 100);
	var timer = 0;

	//set the current image as background
	document.getElementById(divid).style.backgroundImage = "url(" + document.getElementById(imageid).src + ")";

	//make image transparent
	changeOpac(0, imageid);

	//make new image
	document.getElementById(imageid).src = imagefile;

	//fade in image
	for(i = 0; i <= 100; i++) {
		setTimeout("changeOpac(" + i + ",'" + imageid + "')",(timer * speed));
		timer++;
	}
}

function currentOpac(id, opacEnd, millisec) {
	//standard opacity is 100
	var currentOpac = 100;

	//if the element has an opacity set, get it
	if(document.getElementById(id).style.opacity < 100) {
		currentOpac = document.getElementById(id).style.opacity * 100;
	}

	//call for the function that changes the opacity
	opacity(id, currentOpac, opacEnd, millisec)
}


function blender(id_hide, id_show, opac_show, duration) {
    var style_hide = "document.getElementById('" + id_hide + "').style";
    var style_show = "document.getElementById('" + id_show + "').style";
    var display_none  = ".display = 'none'; ";
    var display_block = ".display = 'block'; ";

    var s_ejecutar;

    // Transición de visible a oculto en n segundos
    //opacity(id_hide, 100, 0, duration);
    /* El div a ocultar debe ponerse su display en none para que el div a mostrar
     * ocupe su lugar y no aparezca en otro lado.
     * Debe esperar n segundos antes de ejecutarse (para que se ejecute apenas termine
     * la instrucción anterior). */
    window.setTimeout(style_hide + display_none, 0);
    /* El div a mostrar debe tener opacidad 0 y ser visible para comenzar la transición.
     * Debe esperar n segundos antes de ejecutarse (para que se ejecute apenas termine
     * la primera instrucción de esta función). */
    s_ejecutar = style_show + ".opacity = 0; " +
                 style_show + ".MozOpacity = 0; " +
    	         style_show + ".KhtmlOpacity = 0; " +
    	         style_show + ".filter = 'alpha(opacity=0)'; " +
                 style_show + display_block;
    window.setTimeout(s_ejecutar, 0);
    /* Transición de oculto a visible en n segundos.
     * Igualmente, debe esperar n segundos antes de ejecutarse (para que se ejecute
     * apenas termine la primera instrucción de esta función). */
    s_ejecutar = "opacity('" + id_show + "', 0, " + opac_show.toString() + ", " + duration.toString() + ")";
    window.setTimeout(s_ejecutar, 0);
}