It seems that the common-sense for Augmented Reality is something related to what we see. I found out that I was struck with this "vision" (tum-tum-tss) when I realized that what I wanted is a system to help me aiming the cue, and that doesn't mean this help shall be visual.
So, since I'm still having problems to attach the projector permanently on the ceiling, I've added an audio output to Cassapa, to help the aiming when the projector is not available. It plays an continuous sound when the cue is aiming a ball, and the changes the pitch according to the trajectory forecast. Pitch increases as the probability of the ball hitting the pocket increases.
Currently I'm doing this with FMOD library, which has a non-commercial license, but I'm still looking for a fully open alternative. Since this is functionality is not mandatory for Cassapa, it can be completely removed if you don't agree with free-as-beer-but-not-free-as-speech software.