//Tomasz Lubiński (C)2007 
//www.algorytm.org
//Algorytm kreslenia elipsy

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ComCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    Image: TImage;
    Label4: TLabel;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Edit1: TEdit;
    UpDown1: TUpDown;
    Button1: TButton;
    Edit2: TEdit;
    UpDown2: TUpDown;
    Edit3: TEdit;
    UpDown3: TUpDown;
    Edit4: TEdit;
    UpDown4: TUpDown;
    procedure Button1Click(Sender: TObject);
    procedure ElipsePoints(x: Integer; y: Integer; x_move: Integer; y_move: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}


procedure TForm1.ElipsePoints(x: Integer; y: Integer; x_move: Integer; y_move: Integer);
begin
        Form1.Image.Canvas.Pixels[x+x_move, y+y_move] := clBlack;
        Form1.Image.Canvas.Pixels[x+x_move, -y+y_move] := clBlack;
        Form1.Image.Canvas.Pixels[-x+x_move, -y+y_move] := clBlack;
        Form1.Image.Canvas.Pixels[-x+x_move, y+y_move] := clBlack;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
   x, y, limit, d: Integer;
   x_move, y_move, radius_a, radius_b, radius_a2, radius_b2: Integer;
begin
x_move := StrToInt(Edit1.Text);
y_move := StrToInt(Edit2.Text);
radius_a := StrToInt(Edit3.Text);
radius_b := StrToInt(Edit4.Text);
radius_a2 := radius_a*radius_a;
radius_b2 := radius_b*radius_b;
d := 4*radius_b2 - 4*radius_b*radius_a2 + radius_a2;
limit := (radius_a2*radius_a2) div (radius_a2+radius_b2);
x := 0;
y := radius_b;

	while (x*x < limit) do
           begin
		ElipsePoints(x,y, x_move,y_move);
		if (d > 0) then
                   begin
			d := d + 8*radius_b2*x + 12*radius_b2 - 8*radius_a2*y + 8*radius_a2;
			x := x + 1;
			y := y - 1;
                   end
		else
                   begin
			d := d + 8*radius_b2*x + 12*radius_b2;
			x := x + 1;
                   end;
           end;

radius_a := StrToInt(Edit4.Text);
radius_b := StrToInt(Edit3.Text);
radius_a2 := radius_a*radius_a;
radius_b2 := radius_b*radius_b;
d := 4*radius_b2 - 4*radius_b*radius_a2 + radius_a2;
limit := (radius_a2*radius_a2) div (radius_a2+radius_b2);
x := 0;
y := radius_b;

	while (x*x < limit) do
           begin
		ElipsePoints(y,x, x_move,y_move);
		if (d > 0) then
                   begin
			d := d + 8*radius_b2*x + 12*radius_b2 - 8*radius_a2*y + 8*radius_a2;
			x := x + 1;
			y := y - 1;
                   end
		else
                   begin
			d := d + 8*radius_b2*x + 12*radius_b2;
			x := x + 1;
                   end;
           end;


end;
end.