[Nostalgia]

Доброго времени суток!
При построении четырехугольника возникла проблема, в некоторых случаях он вырисовывается в виде "конфеты". в чем может быть проблема? Для изображения фигур используется компонент Image. Смотреть код жирным шрифтом снизу.

Код:

unit Unit1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, ExtCtrls, Menus;

type
 TForm1 = class(TForm)
   Image1: TImage;
   MainMenu1: TMainMenu;
   N2: TMenuItem;
   N1: TMenuItem;
   N3: TMenuItem;
   N4: TMenuItem;
   N5: TMenuItem;
   N6: TMenuItem;
   N7: TMenuItem;
   N8: TMenuItem;
   N9: TMenuItem;
   procedure FormCreate(Sender: TObject);
   procedure N7Click(Sender: TObject);
   procedure N8Click(Sender: TObject);
   procedure N9Click(Sender: TObject);
   procedure Image1MouseDown(Sender: TObject; Button: TMouseButton;
     Shift: TShiftState; X, Y: Integer);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

var
 Form1: TForm1;
 xx,yy:integer;
 tr, rec, cer:boolean;
 Treangl:array[1..3,1..2] of integer;
 Rectangl:array[1..4,1..2] of integer;
 Elips:array[1..3,1..2] of integer;
 i:integer;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
 xx:=round(Image1.Width/2);
 yy:=round(Image1.Height/2);
 Form1.Image1.Canvas.MoveTo(0,yy);
 Form1.Image1.Canvas.LineTo(Form1.Image1.Width,yy);//OX
 Form1.Image1.Canvas.MoveTo(xx,0);
 Form1.Image1.Canvas.LineTo(xx, Form1.Image1.Height);//OY
 //
 Form1.Image1.Canvas.MoveTo(Form1.Image1.Width,yy);
 Form1.Image1.Canvas.LineTo(Form1.Image1.Width-10, yy-7);
 Form1.Image1.Canvas.MoveTo(Form1.Image1.Width,yy);
 Form1.Image1.Canvas.LineTo(Form1.Image1.Width-10, yy+7);
 //
 Form1.Image1.Canvas.MoveTo(xx,0);
 Form1.Image1.Canvas.LineTo(xx-7,15);
 Form1.Image1.Canvas.MoveTo(xx,0);
 Form1.Image1.Canvas.LineTo(xx+7,15);
 //
 Image1.Canvas.TextOut(xx-20, yy+10, '0,0');
 Image1.Canvas.TextOut(2*xx-10, yy+15, 'X');
 Image1.Canvas.TextOut(xx-15,5,'Y');
 tr:=False;
 rec:=False;
 cer:=False;
end;

procedure TForm1.N7Click(Sender: TObject);
begin
i:=1;
tr:=True;
rec:=False;
cer:=False;
end;

procedure TForm1.N8Click(Sender: TObject);
begin
i:=1;
tr:=False;
rec:=True;
cer:=False;
end;

procedure TForm1.N9Click(Sender: TObject);
begin
i:=1;
tr:=False;
rec:=False;
cer:=True;
end;

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
 Shift: TShiftState; X, Y: Integer);
begin
 if tr=true then
   begin
     if i<=3 then
     begin
       Treangl[i,1]:=x;
       Treangl[i,2]:=y;
       if i=3 then
         begin
Form1.Image1.Canvas.MoveTo(Treangl[1,1], Treangl[1,2]);
Form1.Image1.Canvas.LineTo(Treangl[2,1], Treangl[2,2]);
Form1.Image1.Canvas.LineTo(Treangl[3,1], Treangl[3,2]);
Form1.Image1.Canvas.LineTo(Treangl[1,1], Treangl[1,2]);
         end;
       i:=i+1;
     end;
   end;

if rec=true then
    begin
     if i<=4 then
     begin
       Rectangl[i,1]:=x;
       Rectangl[i,2]:=y;
       if i=4 then
         begin
Form1.Image1.Canvas.MoveTo(Rectangl[1,1], Rectangl[1,2]);
Form1.Image1.Canvas.LineTo(Rectangl[2,1], Rectangl[2,2]);
Form1.Image1.Canvas.LineTo(Rectangl[3,1], Rectangl[3,2]);
Form1.Image1.Canvas.LineTo(Rectangl[4,1], Rectangl[4,2]);
Form1.Image1.Canvas.LineTo(Rectangl[1,1], Rectangl[1,2]);

         end;
        i:=i+1;
     end;
   end;
end;


end.