procedure TIEImageCompareInteraction.PaintBackBuffer(BackBuffer: TIEBitmap);
var
  iev: TImageEnView;
  ww, hh, lx: Integer;
  bmp1, bmp2: TIEBitmap;
begin
  iev := TImageEnView(fParent);

...

  lx := Round( iev.ClientWidth * fLineX );
  if fScreenBitmapX <> lx then
  begin
    // Reset the transition - needed for ImageEn versions <= 13.0.0
    fTransition.CreateBitmap( 0, fScreenBitmap.VclBitmap );    // <<<<<<<<<<<<<< ADD THIS LINE

    // Generate our display image
    fTransition.CreateBitmap( fLineX * 100, fScreenBitmap.VclBitmap );

...
  end;

  fScreenBitmap.DrawToTIEBitmap( BackBuffer, 0, 0 );
end;

procedure TForm4.MoveControl(AControl: TControl; const X, Y: Integer);
var
  lPoint: TPoint;
begin
  lPoint := AControl.Parent.ScreenToClient
    (AControl.ClientToScreen(Point(X, Y)));
     AControl.Left := lPoint.X - AControl.Width div 2;
       if AControl.Left>TImage1.Width then
         AControl.Left:=TImage1.Width;    end;

procedure TForm4.shape1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
    if ssLeft in Shift then
    begin
      MoveControl(Sender as TControl, X, Y);
      TImage0.Width:=shape1.Left-1;
    end
end;

procedure TForm4.FormCreate(Sender: TObject);
begin
  TImage0.Left:=1;
  TImage1.Left:=1;

 TImage0.Top:=1;
  TImage1.Top:=1;
end;

procedure TForm4.FormShow(Sender: TObject);
begin
 TImage0.Width:= TImage1.Width Div 2;
 shape1.Left:=TImage0.Width+1;
shape1.Top:=TImage1.Top;
shape1.Height:=TImage1.Height;
end;

// Slide Transition from old.bmp to new.bmp ensuring that both are shown as the same height
procedure TForm1.btnCompareClick(Sender: TObject);
const
  Display_Zoom = 100;
  Center_Image = True;
var
  bh: Integer;
  iz: Double;
begin
  // Get original image as transition start
  ImageEnView1.IO.LoadFromFile( ExtractFilePath( Application.ExeName ) + 'old.bmp' );
  ImageEnView1.Zoom := Display_Zoom;
  if Center_Image then
    ImageEnView1.CenterImage()
  else
   ImageEnView1.SetViewXY( 0, 0 );

  bh := ImageEnView1.IEBitmap.Height;
  iz := ImageEnView1.Zoom;
  ImageEnView1.PrepareTransition();

  // Load second image as transition result (Zoom to match display size of old image)
  ImageEnView1.IO.LoadFromFile( ExtractFilePath( Application.ExeName ) + 'new.bmp' );
  ImageEnView1.Zoom := iz / ( ImageEnView1.IEBitmap.Height / bh );
  if Center_Image then
    ImageEnView1.CenterImage()
  else
   ImageEnView1.SetViewXY( 0, 0 );

  // Run the transition
  ImageEnView1.TransitionParams.AlternativeStyle := True;  // Include transition line
  ImageEnView1.TransitionParams.WipeLineColor := clYellow;
  ImageEnView1.RunTransition( iettRightLeft, 3000 );       // Wipe Right to Left
end;

<WEBIMG SlideTransition.jpg>