procedure TForm1.ImageEnView1DrawBackBuffer(Sender: TObject);
var
  ix1: Integer;
  iy1: Integer;
  ix2: Integer;
  iy2: Integer;
  iz: double;
begin
  iz := ImageEnView1.Zoom / 100;
  ImageEnView1.BackBuffer.Canvas.Pen.Width := 1;
  ImageEnView1.BackBuffer.Canvas.Pen.Color := clBlue;
  ImageEnView1.BackBuffer.Canvas.Pen.Style := psSolid;
  ImageEnView1.BackBuffer.Canvas.Brush.Style := bsClear;
  ix1 := ImageEnView1.OffsetX*Round(iz);
  iy1 := ImageEnView1.OffsetY*Round(iz);
  ix2 := (ImageEnView1.IEBitmap.Width-1) * Round(iz);
  iy2 := (ImageEnView1.IEBitmap.Height-1) * Round(iz);
  ImageEnView1.BackBuffer.Canvas.Rectangle(ix1, iy1, ix2 + ix1, iy1 + iy2);
  ImageEnView1.BackBuffer.Canvas.Pen.Color := clBlack;
  ImageEnView1.BackBuffer.Canvas.MoveTo((ix2 + ix1) div 2, iy1);
  ImageEnView1.BackBuffer.Canvas.LineTo((ix2 + ix1) div 2, iy1 + iy2);
  ImageEnView1.BackBuffer.Canvas.MoveTo(ix1, iy2 div 2);
  ImageEnView1.BackBuffer.Canvas.LineTo((ix2 + ix1), iy2 div 2);
end;

procedure Tfmain.ImageEnView1DrawBackBuffer(Sender: TObject);
var
  ix1: Integer;
  iy1: Integer;
  ix2: Integer;
  iy2: Integer;
begin
  ix1 := ImageEnView1.OffsetX ;
  iy1 := ImageEnView1.OffsetY ;
  ix2 := ImageEnView1.ExtentX ;
  iy2 := ImageEnView1.ExtentY ;
  
  ImageEnView1.BackBuffer.Canvas.Pen.Width := 1;
  ImageEnView1.BackBuffer.Canvas.Pen.Color := clBlue;
  ImageEnView1.BackBuffer.Canvas.Pen.Style := psSolid;
  ImageEnView1.BackBuffer.Canvas.Brush.Style := bsClear;
  ImageEnView1.BackBuffer.Canvas.Rectangle(ix1, iy1, ix1 + ix2, iy1 + iy2);
  
  ImageEnView1.BackBuffer.Canvas.Pen.Color := clBlack;
  ImageEnView1.BackBuffer.Canvas.MoveTo( ix1 + ix2 div 2, iy1 );
  ImageEnView1.BackBuffer.Canvas.LineTo( ix1 + ix2 div 2, iy1 + iy2);
  ImageEnView1.BackBuffer.Canvas.MoveTo( ix1, iy1 + iy2 div 2);
  ImageEnView1.BackBuffer.Canvas.LineTo( ix1 + ix2, iy1 + iy2 div 2);
end;