This code will crash if there is nothing on the tile, i.e., obj==NULL.
That is why it closed simutrans.
One can certainly think about such functionality (maybe restricted to scenarios). What about adding such functions as member functions to map_object_x?
I do not know if this is an error, but the selection tool does not work with cruses, tunnels and high ways. Does this make sense?
I would like to mark the entrance of a tunnel so that the player notices that the road is badly connected.
Another detail is that the image is not updated instantly, it is always necessary to place the cursor on the marked object so that it is marked / unmarked. Is it possible to solve this?