Get The Feel
A rotary (a.k.a. "spinner") control is a little unusual. It is constrained to a single degree of freedom, and the twisting mechanic is best suited to movement around a central point. Not just any game will lend itself to this dynamic, and there isn't much point in using a rotary control for a game that would be better suited to a more common control scheme.
I had intended to make some sort of tube shooter game for the CoCo3. I would still like to do that, but I don't think I can accomplish that during this month's Retrochallenge event. Consequently, I need something simpler to implement!
I started thinking about simple games and round shapes. Before long, the answer became obvious -- Simon, an 80's classic. The game logic and basic mechanics (e.g. playing sounds) should be simple enough to implement in the allotted time. The rotary control might not seem like an obvious choice, but I think it will map well to Simon's four centrally arranged buttons.
To get started, I knocked-up some code to draw four colored boxes on the screen. I refactored my controller code to buffer the movement indications a bit, so that turning the spinner resulted in controllable selections. I am using a white outline to indicate the currently selected color. Pressing the button changes the outline to match the color of the selected box, making a larger colored box. The larger colored boxes will also be used when the patterns are being played for memorization.
I think that covers the basic mechanics, other than playing the tones. That should be relatively simple -- YMMV, of course! I guess we'll find-out about that soon enough. Until then, stay tuned... :-)