Simulate hair using a Linear Wire modifier

Model courtesy of Tarkan Sarim

You can simulate hair and fur by adding a Linear Wire to your interactive groom description. The wires created by the modifier can be converted to dynamic curves and controlled by a Maya nHair system.

Note: You can also simulate hair using a Guide modifier by following this workflow, although some setting may be different.

This workflow assumes that you have already done the following:

• Created an interactive grooming description, styled the hair, and added a Linear Wire modifier.

  See Create hair and fur using interactive grooming and Work with interactive groom modifiers.

• Created the wires on the surface of the mesh. See Create hair guides using a Guide modifier.

1. In the Interactive Groom Editor, select the Linear Wire modifier.
2. In the Input Wire section of the Attribute Editor, click Make Wires Dynamic.
3. In the Make Guides Dynamic Options window, select the appropriate options, and click Apply and Close.
   Maya converts the wires to input curves, which are listed under Input in Attribute Editor and creates an xgmCurveToSpline_dynamic node. Maya also creates an nHair system with the following objects:

   • hairSystemShape node
   • nucleus node
   • nRigid node, when Collide With Mesh is on in the Make Guides Dynamic Options.
   • Grouped hairSystemFollices.
   • Grouped hairSystemOutputCurves.

   See information on these objects, see nHair nodes.

4. Play back the simulation to see the dynamic motion of the wire input curves, then rewind to the start frame.
5. In the Interactive Groom Editor, select the Linear Wire modifier.
6. In the Linear Wire Modifier group of the Attribute Editor, beside Reference State, click Update.

   This sets the hair's start pose as the initial frame of the hair simulation.

   Note: Guide modifiers do not have a Reference State attribute.
7. Play the simulation, then rewind to the start frame.

   The hairs now follow the motion of the dynamic wires.

8. If desired, create an Alembic cache of the hair simulation by selecting the description the Interactive Groom Editor, then Description > Cache > Create New Cache.

   See Create an interactive groom hair cache.

   When you play back the simulation, all of the XGen data is read back from the cache file node on disk.

You can use these dynamic wires to drive the hair simulation in other descriptions. See Control multiple descriptions using a Guide or Linear Wire modifier.

Control the hair simulation

Use the nucleus and nHair system nodes to adjust the simulation-related settings. For example:

• Create an nCache of the hair simulation to accelerate the playback. See Create or Import nCaches.
• In the Collisions group of the hairSystemShape node attributes, turn on Self Collide. The dynamic wires now self collide so they do not intersect with each other.

  See nHair Collision attributes.

Related topics

• Animate hairs by keying a Guide modifier