procedure TDocEditorForm.ImageEnView1MouseDown(Sender: TObject;
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin

with ImageEnView1, canvas do
  begin
    If checkbox1.checked then
    begin
    pen.width:=15;
    pen.color:=clwhite;//acts as an eraser

    end else
    begin
    pen.width:=3;
    pen.color:=clblack;
    end;

    drawing:=true; //public variable
    moveto(x,y);
  end;
end;

procedure TDocEditorForm.ImageEnView1MouseUp(Sender: TObject;
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin

   drawing := False;
end;

procedure TDocEditorForm.ImageEnView1MouseMove(Sender: TObject;
  Shift: TShiftState; X, Y: Integer);
begin
  If drawing
  then with imageEnView1 do
  begin
    cursor:=crNone; {to keep cursor redraw from erasing part of the line}
    canvas.lineto(x,y);
    cursor:=crdefault;
  end;
end;

unit Unit1;

interface

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

type
  TForm1 = class( TForm )
    Panel1: TPanel;
    StatusBar1: TStatusBar;
    ImageEnView1: TImageEnView;
    CheckBox1: TCheckBox;
    Button1: TButton;
    Button2: TButton;
    procedure ImageEnView1MouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: integer );
    procedure ImageEnView1MouseUp( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: integer );
    procedure ImageEnView1MouseMove( Sender: TObject; Shift: TShiftState; X, Y: integer );
    procedure Button1Click( Sender: TObject );
    procedure FormCreate( Sender: TObject );
    procedure Button2Click( Sender: TObject );
  private
    { Private declarations }
    Drawing: boolean;
    StartX: integer;
    StartY: integer;
    LastX: integer;
    LastY: integer;
    APenSize: integer;
    procedure MyUndo( ie: TImageEnView );
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses imageenproc;
{$R *.dfm}

procedure TForm1.MyUndo( ie: TImageEnView );
var
  x1, y1, x2, y2: integer;
begin
  x1 := StartX;
  y1 := StartY;
  x2 := LastX;
  y2 := LastY;
  OrdCor( x1, y1, x2, y2 );
  ie.Proc.UndoRect( x1 - APenSize, y1 - APenSize, x2 + APenSize, y2 + APenSize );
end;

procedure TForm1.Button1Click( Sender: TObject );
begin
  ImageEnView1.LayersAdd;
  // render white bitmap on layer x
  with ImageEnView1.CurrentLayer do
    ImageEnView1.Proc.Fill( clWhite );
  ImageEnView1.Update;
end;

procedure TForm1.Button2Click( Sender: TObject );
begin
  if ImageEnView1.LayersCount > 1 then
    ImageEnView1.LayersRemove( ImageEnView1.LayersCurrent )
  else
    ShowMessage( 'No Layer To Remove.' );
end;

procedure TForm1.FormCreate( Sender: TObject );
begin
  // render white bitmap on layer 0
  ImageEnView1.Proc.Fill( clWhite );
  ImageEnView1.Update;
end;

procedure TForm1.ImageEnView1MouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: integer );
begin
  if ImageEnView1.MouseCapture then
  begin
    with ImageEnView1 do
    begin
      // prevent exception by trying to draw outside of the bitmap
      if ( XScr2Bmp( X ) >= 0 ) and ( XScr2Bmp( X ) <= Bitmap.Width - 1 ) and ( YScr2Bmp( Y ) >= 0 ) and
        ( YScr2Bmp( Y ) <= Bitmap.Height - 1 ) then
      begin
        Proc.SaveUndo( ieuImage );
        StartX := XScr2Bmp( X );
        StartY := YScr2Bmp( Y );
        with Bitmap.Canvas do
        begin
          if CheckBox1.Checked then
          begin
            APenSize := 15;
            Pen.Width := 15;
            Pen.Color := clWhite; // acts as an eraser
            Brush.Color := clWhite;
          end
          else
          begin
            APenSize := 3;
            Pen.Width := 3;
            Pen.Color := clBlack;
            Brush.Color := clBlack;
          end;
          Drawing := true; // private variable
        end;
      end;
    end;
  end;
end;

procedure TForm1.ImageEnView1MouseMove( Sender: TObject; Shift: TShiftState; X, Y: integer );
begin
  if ImageEnView1.MouseCapture then
  begin
    if Drawing then
    begin
      with ImageEnView1 do
      begin
        // prevent exception by trying to draw outside of the bitmap
        if ( XScr2Bmp( X ) >= 0 ) and ( XScr2Bmp( X ) <= Bitmap.Width - 1 ) and ( YScr2Bmp( Y ) >= 0 ) and
          ( YScr2Bmp( Y ) <= Bitmap.Height - 1 ) then
        begin
          MyUndo( ImageEnView1 );
          with ImageEnView1 do
          begin
            Bitmap.Canvas.MoveTo( StartX, StartY );
            Bitmap.Canvas.LineTo( XScr2Bmp( X ), YScr2Bmp( Y ) );
            Cursor := crDefault;
          end;
          // for undo method
          LastX := ImageEnView1.XScr2Bmp( X );
          LastY := ImageEnView1.YScr2Bmp( Y );
        end;
      end;
    end;
  end;
end;

procedure TForm1.ImageEnView1MouseUp( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: integer );
begin
  Drawing := False;
end;

end.