anchor.diff:  
   { TMapRect }
   
  +constructor TMapRect.Create;
  +begin
  +  Clear();
  +end;
  +
   function TMapRect.Left: integer;
   begin
     Result := FTopLeft.x;
  
positive.code:   FWidth:=0;
  end;
  
  procedure TMapRect.SetFromCenter(X, Y, Width, Height: integer);
  begin
    Assert(width mod 2 = 1);
    Assert(Height mod 2 = 1);
  
negative.code: type
    { TMapRect }
  
    TMapRect = object
      FTopLeft: TMapCoord;
      FWidth,FHeight: Integer;
  
      constructor Create(); //empty
  
      function Left(): integer;
      function Right(): integer;
  