консультация по методу TMapScreen.ScreenRepaint

procedure TMapScreen.ScreenRepaint(aPaintRectInWin : PRect);
var
  rect1 : TRECT;
  position : TPOINT;
  ScreenDc : HDC;
begin

  ScreenDc := 0;

 try

  if FMapScreen = 0
     then exit;

  FPaintPosHor := MapLeft; // 16/01/2004
  FPaintPosVer := MapTop;

  if aPaintRectInWin <> nil
     then begin

       position.x := aPaintRectInWin.Left;
       position.Y := aPaintRectInWin.Top;

       rect1 := rect(aPaintRectInWin.Left   + FPaintPosHor,
           aPaintRectInWin.Top    + FPaintPosVer,
           aPaintRectInWin.Right  + FPaintPosHor,
           aPaintRectInWin.Bottom + FPaintPosVer);

     end
     else begin

       position.x := 0;
       position.Y := 0;

       rect1 := rect(FPaintPosHor,
                     FPaintPosVer,
           FPaintPosHor + width,
           FPaintPosVer + height);
     end;

  pf_scrDrawMap(FMapScreen, rect1, position);

  FScreenUpdateBeforePaint := false;  // 27/04/2009

  if Assigned(FOnMapScreenUpdate)
     then FOnMapScreenUpdate(Self, rect1, position.x, position.y);

//  FScreenUpdateBeforePaint := false; 27/04/2009

  except
    if ScreenDc <> 0
       then pf_scrReleaseDC(FMapScreen);
  end;

end;

var
  ScreenDc : HDC;
begin
  ScreenDc := 0;
    ....
  try
 ....
  except
    if ScreenDc <> 0
       then pf_scrReleaseDC(FMapScreen);
  end;
end;