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Constraints

A constraint couples one placement's transform to another's. Use them when a placement should follow some other placement's position, rotation, scale, or any combination, without parenting the two.

The five constraints

Constraint Menu Channels carried
Parent Rigging > Constraints > Parent Translate + Rotate + Scale (everything)
Point Rigging > Constraints > Point Translate only
Orient Rigging > Constraints > Orient Rotate only
Aim Rigging > Constraints > Aim Rotation so the constrained's forward axis aims at the target
Scale Rigging > Constraints > Scale Scale only

Create a constraint

  1. Click the target placement first (the source of motion).
  2. Shift-click the constrained placement (the follower).
  3. Choose a constraint from the menu.

The constraint is stored on the constrained placement and re- evaluates every frame.

Parent vs Parenting

Two confusingly-named concepts:

  • Edit > Parent: hierarchical parent. The constrained placement becomes a child in the scene graph; its transforms are interpreted in the parent's local space.
  • Constraints > Parent: keeps the placement at the same scene level but copies the target's world transform each frame.

Use Edit > Parent when both placements should move together as a group. Use Constraints > Parent when the follower should mirror the target's world position but keep its own scene-graph parent (useful for "this prop follows the character's hand without becoming part of the character's hierarchy").

Aim constraint

Aim is the trickiest. It rotates the constrained so its forward axis points at the target's position. Common uses:

  • Eyes following the camera or another character.
  • A spotlight tracking a moving subject.
  • An IK arm rotating its hand to point at a target.

Properties:

  • Aim vector: which local axis points at the target (X by default).
  • Up vector: which local axis stays oriented "up".
  • World up object: what defines "up" (defaults to world Y).

Mixing multiple constraints

A placement can carry several constraints simultaneously. They evaluate in stack order; each constraint operates on whatever the previous one produced. Reorder by dragging in the Properties pane.

Common mix: Point + Orient + Scale = same as Parent, but you can animate the Point's weight to slide the follower in/out without also blending rotation or scale.

Weight

Every constraint has a 0..1 weight. Animate the weight to fade a constraint in or out. At 0 the constrained's own transform takes over; at 1 the constraint fully controls.

Clear

Rigging > Constraints > Clear (Selected) removes every constraint on the selected placement (asks for confirmation).

To remove just one constraint, expand the Properties pane's Constraints section and click the X next to the entry you want gone.

Performance

Constraints evaluate per frame on the CPU as part of the scene graph update. Each costs about 1 μs. A rig with 50 constraints is sub-millisecond per frame.

See also