[etzhzrqk] Virtual duck hunt

The killer app of head tracking virtual reality is of course a first-person shooter game.  We imagine a duck-hunting game in which the target moves in a pattern: a simple pattern on early levels, an more complicated one in later levels.  One way to create periodic yet complicated movement in 3D is epicycles on epicycles.

Virtual reality can provide the equivalent of tracer ammunition, illegal or unsafe in the real world.

We want some segments in which the target is moving mostly directly towards or away from the shooter, making for an easier shot with less angular speed.  Easiest is the target moving in a circle coplanar with the shooter, circling a distant point.