The rendering mode for legacy particles.
This is used by the ParticleRenderer to determine how to render the particles.
| Billboard | Render the particles as billboards facing the player. (Default) | 
| Stretch | Stretch particles in the direction of motion. | 
| SortedBillboard | Sort the particles back-to-front and render as billboards. | 
| HorizontalBillboard | Render the particles as billboards always facing up along the y-Axis. | 
| VerticalBillboard | Render the particles as billboards always facing the player, but not pitching along the x-Axis. |