Moov Physics Operator
Moov Physics is Ornatrix's in-house physics engine for simulating hair motion. The Moov Physics operator gives you a real-time interface to that engine, so you can simulate hair swaying, settling, and reacting to movement directly in the App. It is the operator to reach for when you need true dynamics rather than the faked motion of the Oscillator Operator or Gravity Operator.
Simulating hair
Add the Moov Physics operator to a groom and play the timeline to run the simulation: the hair responds to motion of the underlying object and to forces such as gravity, building up believable follow-through and settling. Because it runs in real time, you can adjust the simulation and immediately see the effect.
Collisions
The simulation collides the hair with meshes. The object the hair grows on is always available as a collider: turn on Collide With Base Mesh in the Collisions group to keep the strands out of it. Any other object in the scene can be added as a collider through the operator's Collision Meshes list: click Add and pick the object, or wire its mesh output into the Collision Meshes port in the Node Graph. Collide With Meshes switches those extra colliders on and off, and removing an object from the list stops it from colliding.
Collisions are tested per strand point, so Particle Radius is the parameter that keeps the hair off a surface: it defaults to 0, and raising it (0.5 or so in a scene modelled in centimeters) makes the strands rest on the surface instead of grazing through it. Collision Tolerance, Friction Coefficient and Restitution Coefficient refine how the contact behaves. Strands with few points can still straddle a surface feature between two of their points, so give simulated guides enough points with the Detail Operator when they need to hug a collider closely.
A collider is used where its mesh sits in the scene when it was created or imported. Moving it afterwards with the transform tool moves the object in the viewport but not for the simulation.
Scriptability
Moov is extensible through Python. It ships with scripts that provide different simulation behaviors, and technical artists can write their own to achieve more complex or specialized results. See Scripting with the Python Console.
Working with simulations
- Set the frame range to cover the motion you want to simulate.
- Simulate a sparse set of guides and let the dense hair follow them, which is far faster than simulating every hair. See Adopt External Guides.
- Once you are happy with a simulation, bake it so it plays back without recomputing. See Baking Hair and Guides and Animation Cache Operator.
Related
- Oscillator Operator and Gravity Operator - cheaper, non-simulated motion and settling.
- Resolve Collisions Operator - art-directable collisions without full simulation.