The particle curve mode.
This is used by MinMaxCurve to determine which mode to evaluate curves in.
| Constant | Use a single constant for the MinMaxCurve. |
| Curve | Use a single curve for the MinMaxCurve. |
| TwoCurves | Use a random value between 2 curves for the MinMaxCurve. |
| TwoConstants | Use a random value between 2 constants for the MinMaxCurve. |