Create a form with rounded corners

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;