'spherical': lies square to the screen however the camera turns. Suits glows, impact
flashes, icons and distance markers.
'cylindrical': turns around its own up axis toward the camera but never tips, so it stays
planted. Suits trees, grass, crowd cutouts and flat stand-ins for distant models.
How a mesh turns to face the camera; see Mesh3D#billboardMode
'none': no turning; the mesh draws as authored.'spherical': lies square to the screen however the camera turns. Suits glows, impact flashes, icons and distance markers.'cylindrical': turns around its own up axis toward the camera but never tips, so it stays planted. Suits trees, grass, crowd cutouts and flat stand-ins for distant models.