I'll try to make this a short a story as posible and get to the question, but I would prefer that you know exactly how I got to this question.
So, I've been cosidering lately, doing some sort of rotary hack to my t-stick plus similar to mr.Curmudgeon's design.
In my lookings arround I was checking out Druin's encoder board and found a list of games on his site that it works well with, according to Druin.
Here's the page with the list.
CLICK MEI started sorting through MAME, putting the games into a custom folder all the while checking out some of the games I haven't tried before and making sure they were infact rotary joy games. Well, durring my sort, I came to Xybots and it wasn't listed as having Trackball support as all other rotary/spinner games do, so I popped it open and checked the controls. For those who haven't played Xybots on MAME, it has a rotate left and rotate right button rather than the "Dial" that rotary joy games.
So I checked it out on KLOV and apparently it uses a joystick that has a self-centering rotation with a button at the limmits of the rotation.
Then it hits me, since Druin's interface sends a keypress for every click on a mechanical rotary it will obviously work with this game, afterall it is looking for a single button press...
Now this is the part that is stumping me. How would one with a OPTICAL rotary joystick control the rotation? Is there a different version of MAME that allows for this, analog+ perhaps? I can't think of any type of program that would allow the mouse axis to be interpreted by the PC as a button press...
I suppose I could just use 2 of the other 6 buttons on my CP for the left and right rotations, but I thought I'd ask to see if it is posible to use a optical rotary first.