Dr. Dobb's Sourcebook January/February 1997
{ Region is relative to window area }
GetWindowRect(handle,r);
{ normalize so that 0,0 is top/left }
r.right:=r.right-r.left;
r.bottom:=r.bottom-r.top;
r.left:=0;
r.top:=0;
rgn:=CreateEllipticRgn(0,0,r.right,r.bottom);