centering a div on user screen fails with iframe

the javascript below centers a div on the users screen.
it works perfect until you put the code into an iframe.
so the question is: how can I get this to work inside of an iframe?
so far I have narrowed it down to the fact that
scrolledY is always zero in the iframe.

function showdeadcenterdiv(Xwidth,Yheight,divid) {
// First, determine how much the visitor has scrolled

var scrolledX, scrolledY;
if( self.pageYOffset ) {
scrolledX = self.pageXOffset;
scrolledY = self.pageYOffset;
} else if( document.documentElement && document.documentElement.scrollTop ) {
scrolledX = document.documentElement.scrollLeft;
scrolledY = document.documentElement.scrollTop;
} else if( document.body ) {
scrolledX = document.body.scrollLeft;
scrolledY = document.body.scrollTop;
}

// Next, determine the coordinates of the center of browser's window

var centerX, centerY;
if( self.innerHeight ) {
centerX = self.innerWidth;
centerY = self.innerHeight;
} else if( document.documentElement && document.documentElement.clientHeight ) {
centerX = document.documentElement.clientWidth;
centerY = document.documentElement.clientHeight;
} else if( document.body ) {
centerX = document.body.clientWidth;
centerY = document.body.clientHeight;
}

// Xwidth is the width of the div, Yheight is the height of the
// div passed as arguments to the function:
var leftOffset = scrolledX + (centerX - Xwidth) / 2;
var topOffset = scrolledY + (centerY - Yheight) / 2;
// The initial width and height of the div can be set in the
// style sheet with display:none; divid is passed as an argument to // the function
var o=document.getElementById(divid);
var r=o.style;
r.position='absolute';
r.top = topOffset + 'px';
r.left = leftOffset + 'px';
r.display = "block";
} 

Code (markup):

 

I needed to use parent.document