Fill Rectangle Fillrect Method

procedure TForm1.BitBtn5Click(Sender: TObject);
//fillrect bm
var n : integer;
begin
with bm do with canvas do
begin
brush.style := bssolid;
brush.color := $808080;
t1 := gettickcount;
for n := 0 to 9999 do
fillrect(rect(0,0,width,height));
t2 := gettickcount;
end;
showtime(100000000);
end;