A solid cylinder zone aligned to +Y, centred at (x, y, z) — pillars, columns of
light/fire, beam volumes. A true 3D volume, so it works as a CrossZone
boundary (_dead kills particles that leave it; _bound reflects off the side
wall). v1 axis-aligned to +Y; arbitrary axis is a follow-up.
A solid cylinder zone aligned to +Y, centred at (x, y, z) — pillars, columns of light/fire, beam volumes. A true 3D volume, so it works as a
CrossZoneboundary (_deadkills particles that leave it;_boundreflects off the side wall). v1 axis-aligned to +Y; arbitrary axis is a follow-up.