| XSIMR_CE_CONSTANT |
The values of the end points extend to infinity |
| XSIMR_CE_END_GRADIENT |
The end segments extend to infinity |
| XSIMR_CE_CYCLE |
The curve cycles indefinitely in both directions, each curve starting on the same value |
| XSIMR_CE_CYCLE_RELATIVE |
The curve cycles indefinitely in both directions, but each curve after the original starts on the end point of the previous curve, and each curve before ends on the start point of the next. |