Круг на паинт боксе

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls;
 
type
  TForm1 = class(TForm)
    PaintBox1: TPaintBox;
    Timer1: TTimer;
    procedure PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure draw;
    procedure PaintBox1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
  x0,y0,x1,y1:integer;
  start:boolean;
implementation
 
uses Math;
 
{$R *.dfm}
 
procedure TForm1.PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
 
begin
if Button=mbMiddle then begin
  x0:=x;
  y0:=y;
  start:=true;
  draw;
  end;
end;
 
procedure TForm1.draw;
begin
if not start then exit;
if (x1<>0)and(y1<>0) then
if x0>x1 then x0:=x0-1 else x0:=x0+1;
if y0>y1 then y0:=y0-1 else y0:=y0+1;
  with PaintBox1.Canvas do begin
    Repaint;
    Brush.Color:=clred;
    Ellipse(x0-10,y0-10,x0+10,y0+10);
  end;
end;
 
procedure TForm1.PaintBox1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
x1:=x;
y1:=y;
Timer1.Enabled:=true;
end;
 
procedure TForm1.Timer1Timer(Sender: TObject);
begin
draw;
end;
 
end.