some days I though about how funny it would be to control openttd's road vehicles directly. I took as a small exercise to work myself into the codebase and finished it last night.
Note: The patch is for the SDL version only.
What you can do:
(all commands are transferred to the vehicle through its detail window)
keypad minus: toggle between normal control and direct control mode
kp 4: steer left
kp 6: steer right
kp 5: drive straight ahead (may cancel a former request to steer or turn)
kp enter: turn around
kp 8: increase tempomat speed
kp 2: decrease tempomat speed
kp 0: full stop (tempomat speed to zero)
kp plus: full throttle (tempomat speed to max_speed)
Note that although it is named direct control the vehicle works according to the game's rules. that means that you cannot leave the road tiles with this. furthermore the algorithm automatically adjusts movement if you try to steer in an invalid direction.
the steer commands are "executed" when the vehicle enters a new tile.
In dc mode the detail window will shows your current command and tempomat speed in green and the real velocity in black.
"for what is this useful?"
For nothing really. I did it for fun and to train my C skills a bit. furthermore
its the "matrix-style" of free software: I have the tools and the knowledge to modify the world, so why not do it.
Maybe someone else gets inspired to do something useful out of this (taxi driving? what about this mechwarrior thingie someone spoke on this board?).
here is a screenshot:
the patch can be applied to the openttd 0.4.0 sources.
beware: I modified the language files english.txt and german.txt a bit. OTTD will crash if you use another language without having defined the few extra strings. add them yourself (its easy look at the last lines in english.txt) or use english/german.
have fun

thebohemian