Draw in canvas

Source Code :

unit Mouse_Event_Unit1;

interface

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

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    Image1: TImage;
    Panel2: TPanel;
    SpinEdit1: TSpinEdit;
    SpinEdit2: TSpinEdit;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    procedure Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure Image1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Image1MouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormCreate(Sender: TObject);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  MouseButtonIsDown: boolean;   // indicates if the mouse button is down

implementation

{$R *.DFM}

procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  {if the mouse button is down, draw a line}
  if MouseButtonIsDown then
    Image1.Canvas.LineTo(X,Y);
end;

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  {if the mouse button is not down, move the initial drawing position}
  if not MouseButtonIsDown then
    Image1.Canvas.MoveTo(X,Y);

  {indicate that the mouse button is down so that drawing will occur}
  MouseButtonIsDown := TRUE;

  {if the right mouse button was clicked...}
  if Button = MBRight then
  begin
    {...while the mouse button is held down...}
    while MouseButtonIsDown = TRUE do
    begin
      {...simulate mouse movement by the specified amounts. the image
       continues to receive regular mouse messages as if the mouse was
       under user control}
      Mouse_Event(MOUSEEVENTF_MOVE,SpinEdit1.Value,SpinEdit2.Value,0,0);

      {update the screen and pause for a short amount of time}
      Application.ProcessMessages;
      Sleep(10);
    end;
  end;
end;

procedure TForm1.Image1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  {set the mouse button down variable to off}
  MouseButtonIsDown := FALSE;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  {initialize the initial drawing position}
  Image1.Canvas.MoveTo(10,10);
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  {initialize the mouse button down variable}
  MouseButtonIsDown := FALSE;
end;

end.