Currently, an X-shaped cursor ('./data/base/images/intfac/image_cursor_notpos.png') indicates moving to cliffs and certain buildings is not possible. It should indicate all unpassable tiles, unlike below: The minimap lacks that cursor altogether, which is often a problem when units are sent ahead with queue orders: There is no feedback for exceeding structure limits in queue orders. I suggest to show the X-shaped cursor immediately when trying to place an impossible building along with a warning: "Cannot build cyborg factory, structure limit is 1": I used maim to capture screenshots with cursor.
If units are selected and the X-shaped cursor is shown (including suggested uses above) the 'fail' sound './data/base/audio/sfx/interfce/beep8.ogg' should be played. It is currently reserved for attempts to build burning oil dericks and some obscure situations. I think overall this would be an excellent improvement, though there are disadvantages:
- Burning oil derricks are valid as destinations and in queue orders. To avoid confusion, I suggest not to play the sound for burning oil derricks since a warning message is given anyway.
- Units would need to be deselected before clicking on e.g. a power generator unless the 'fail' sound can be tolerated.