The rendering mode for particle systems (Shuriken).
This is used by the ParticleSystemRenderer to determine how to render the particles.
| Billboard | Render particles as billboards facing the active camera. (Default) | 
| Stretch | Stretch particles in the direction of motion. | 
| HorizontalBillboard | Render particles as billboards always facing up along the y-Axis. | 
| VerticalBillboard | Render particles as billboards always facing the player, but not pitching along the x-Axis. | 
| Mesh | Render particles as meshes. | 
| None | Do not render particles. |