{
 Die CreateRoundRectRgn lasst eine Form mit abgerundeten Ecken erscheinen.
 The CreateRoundRectRgn function creates a rectangular
 region with rounded corners
}
 procedure TForm1.FormCreate(Sender: TObject);
 var
  rgn: HRGN;
 begin
  Form1.Borderstyle := bsNone;
  rgn := CreateRoundRectRgn(0,// x-coordinate of the region's upper-left corner
  0, // y-coordinate of the region's upper-left corner
  ClientWidth, // x-coordinate of the region's lower-right corner
  ClientHeight, // y-coordinate of the region's lower-right corner
  40, // height of ellipse for rounded corners
  40); // width of ellipse for rounded corners
 SetWindowRgn(Handle, rgn, True);
 end

 { The CreatePolygonRgn function creates a polygonal region. }

 procedure TForm1.FormCreate(Sender: TObject);
 const
  C = 20;
 var
  Points: array [0..7] of TPoint;
  h, w: Integer;
 begin
  h := Form1.Height;
  w := Form1.Width;
  Points[0].X := C; Points[0].Y := 0;
  Points[1].X := 0; Points[1].Y := C;
  Points[2].X := 0; Points[2].Y := h - c;
  Points[3].X := C; Points[3].Y := h;
  Points[4].X := w - c; Points[4].Y := h;
  Points[5].X := w; Points[5].Y := h - c;
  Points[6].X := w; Points[6].Y := C;
  Points[7].X := w - C; Points[7].Y := 0;
  SetWindowRgn(Form1.Handle, CreatePolygonRgn(Points, 8, WINDING), True);
 end;