Is TChan a sensible choice of chan for events? Should there be some interface
for subscribing to events by type that registers and unregisters callbacks as
needed?

Figure out what rotation should actually result from up, down, etc., and be
consistent across keyboard, mouse, joystick. For example, left and right should
produce a y-axis rotation. But what do negative and positive rotation mean in
OpenGL?

Find pain points in implementation and use them for inspiration for
higher-level API and/or utility functions.
1.) The directional pad on my PS3 controller corresponds to buttons 4..7 for
    up, right, down, left. It's annoying to extract just those.