unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, ExtCtrls,
  StdCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Image1: TImage;
    Label1: TLabel;
    Shape1: TShape;
    Timer1: TTimer;
    procedure FormCreate(Sender: TObject);
    procedure Image1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Image1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer
      );
    procedure Timer1Timer(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;
  speed: single;

implementation

{$R *.lfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Image1.Canvas.Brush.Color := clWhite;
  Image1.Canvas.FillRect(Image1.ClientRect);
end;

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbRight then begin
    Shape1.Left := round(x - Shape1.Width/2);
    Shape1.Top := round(y - Shape1.Height/2);
    Shape1.Visible := true;
    speed := 0;
  end;
end;

procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if ssLeft in Shift then begin
    Image1.Canvas.Pen.Width := 50;
    Image1.Canvas.Pen.Style := psSolid;
    Image1.Canvas.LineTo(x, y);
  end else begin
    Image1.Canvas.MoveTo(x, y);
  end;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var
  x, y: integer;
begin
  if Shape1.Visible then begin
    Shape1.Top := Round(Shape1.Top + speed);
    speed := speed + 1;
    if Shape1.Top > ClientHeight then Shape1.Visible := false;

    x := round(Shape1.Left + Shape1.Width/2);
    y := round(Shape1.Top + Shape1.Height/2);
    if Image1.Canvas.Pixels[x, y] = clBlack then begin
      Shape1.Visible := false;
      Image1.Canvas.Pen.Style := psClear;
      Image1.Canvas.Ellipse(round(x-speed), round(y-speed), round(x+speed), round(y+speed));
    end;
  end;
end;

end.