Are Cone spells three-dimensional geometric shape that tapers smoothly?

@Mazoshi1987Are Cone spells three-dimensional geometric shape that tapers smoothly? Or just a 5ft wide triangle shape? depends on detail DM wants – I use smooth, 3d version, but I also don't use minis or a grid

— (((Mike Mearls))) (@mikemearls) July 21, 2016