Arcane University:Nifskope Prismatic Constraints

Prismatic constraints allow a rigidbody to slide along a fixed line between two points. They are sometimes called rail constraints in other engines as they are alike a train moving along a rail. The prismatic constraints used by the Creation Engine optionally allow the sliding rigidbody to rotate about as it slides, though it is more common to use a fixed rotation.

https://i.imgur.com/5zrFQB0.gif (TODO get this uploaded. I don't have permissions I think)

Axis Configuration

For A & B each, a prismatic constraint has three properties that control the axis that the target rigidbody moves along:

• Sliding: Controls the axis which the rigidbody slides along.
• Rotation: Lock or constrain the rotation axes allowed for the rigidbody
• Plane: Reference plane for rotation

Bethesda rarely (if ever) uses prismatic constraints in their games, so third-party tooling support is similarly minimal. The Havok > A -> B option usually available to constraints in NifSkope, for instance, does not work, and the B properties must be set manually.

The direction of the prismatic constraint can be inverted by multiplying all properties by -1. This is mostly useful for editor intuition (e.g. make max distance apply to the forward direction instead of backwards) since the constraint position cannot be read in-game without the use of the script extender.

Common Configurations

Property	X Axis Slide	Y Axis Slide	Z Axis Slide
Sliding A & B	(1, 0, 0)	(0, 1, 0)	(0, 0, 1)
Rotation A & B	(0, 1, 0)	(0, 0, 1)	(1, 0, 0)
Plane A & B	(0, 0, 1)	(1, 0, 0)	(0, 1, 0)