anchor.diff:      FWidth,FHeight: Integer;
   
       constructor Create(); //empty
  +    constructor SetFromCenter(X,Y, Width,Height: integer);
   
       function Left(): integer;
       function Right(): integer;
  
positive.code:   FWidth:=Width;
    FHeight:=Height;
  end;
  
  
  { TTileCompare }
  
  
negative.code:     destructor Destroy; override;
  
    end;
  
    { TEditTerrain }
  
    TEditTerrain = class(TMapUndoItem)
    strict private
  