// Ellipse um ein Rechteck 
 
procedure Ellipse_aussen(cnv: TCanvas; x1, y1, x2, y2: integer; Farbe: TColor); 
var 
  dy, dx, xx1, yy1, yy2, xx2: integer; 
  dff, wrzl2: double; 
begin 
  cnv.pen.color := Farbe; 
  dx := (x2 - x1); 
  dy := (y2 - y1); 
  wrzl2 := sqrt(2); 
  dff := (dy * wrzl2 - dy) / 2; 
  yy1 := round(y1 - dff); 
  yy2 := round(y2 + dff); 
  dff := (dx * wrzl2 - dx) / 2; 
  xx1 := round(x1 - dff); 
  xx2 := round(x2 + dff); 
  cnv.ellipse(xx1, yy1, xx2, yy2); 
end; 
 
// Rechteck innerhalb einer Ellipse 
 
procedure Rechteck_innen(cnv: TCanvas; x1, y1, x2, y2: integer; Farbe: TColor); 
var 
  dy, dx, xx1, yy1, yy2, xx2: integer; 
  dff, wrzl2: double; 
begin 
  cnv.pen.color := Farbe; 
  dx := (x2 - x1); 
  dy := (y2 - y1); 
  wrzl2 := sqrt(2); 
  dff := (dy / wrzl2 - dy) / 2; 
  yy1 := round(y1 - dff); 
  yy2 := round(y2 + dff); 
  dff := (dx / wrzl2 - dx) / 2; 
  xx1 := round(x1 - dff); 
  xx2 := round(x2 + dff); 
  cnv.rectangle(xx1, yy1, xx2, yy2); 
end; 
 
// Kreis um ein Rechteck  

procedure Kreis_aussen(cnv: TCanvas; x1, y1, x2, y2: integer; Farbe: TColor); 
var 
  dx, dy, c: integer; 
begin 
  cnv.pen.color := Farbe; 
  dx := x2 - x1; 
  dy := y2 - y1; 
  c := round(sqrt(sqr(dx) + sqr(dy)) / 2); 
  dx := round(dx / 2) + x1; 
  dy := round(dy / 2) + y1; 
  cnv.ellipse(dx - c, dy - c, dx + c, dy + c); 
end; 

//-------------------------------------------------------------

// Beispielaufruf Ellipse 
 
procedure TForm1.Button1Click(Sender: TObject); 
var x1, x2, y1, y2: integer; 
begin 
  x1 := 100; 
  y1 := 100; 
  x2 := 200; 
  y2 := 150; 
  Canvas.brush.style := bsClear; 
  Canvas.pen.color := clBlack; 
  Canvas.rectangle(x1, y1, x2, y2); 
 
  Ellipse_aussen(Canvas, x1, y1, x2, y2, clBlue); 
end; 
 
 
// Beispielaufruf Rechteck 
 
procedure TForm1.Button2Click(Sender: TObject); 
var x1, x2, y1, y2: integer; 
begin 
  x1 := 279; 
  y1 := 90; 
  x2 := 421; 
  y2 := 160; 
  Canvas.brush.style := bsClear; 
  Canvas.pen.color := clBlue; 
  Canvas.ellipse(x1, y1, x2, y2); 
 
  Rechteck_innen(Canvas, x1, y1, x2, y2, clBlack); 
end;


// Beispielaufruf Kreis

procedure TForm1.BitBtn2Click(Sender: TObject); 
var x1, x2, y1, y2: integer; 
begin 
  x1 := 100; 
  y1 := 100; 
  x2 := 200; 
  y2 := 150; 
  Canvas.brush.style := bsClear; 
  Canvas.pen.color := clBlack; 
  Canvas.rectangle(x1, y1, x2, y2); 
 
  Kreis_aussen(Canvas, x1, y1, x2, y2, clRed); 
end;