Ping pong
A ball bounces around a black court and every wall hit rings out as a pitched bip with an expanding ripple — trajectory and beat are pure functions of time.
A single white ball ricochets between the edges of the frame, leaving thin rings that expand and fade from every point of impact. Pointers can add more balls that simply track the finger or mouse; the boundary is the only thing that makes a sound, and each hit's pitch depends on where along the wall it lands.
There is no physics engine: the position is a pure function of time that folds the travelled distance into reflections, and a bounce is detected as that fold count ticking up, which triggers the synthesised bip. Because nothing depends on frame rate or chance, the same trajectory plays the same rhythm in the live preview and in an offline render.
