Adopt External Guides 

The Adopt External Guides operator drives a dense hair groom with a small set of externally animated guides. This is much like skinning a character mesh with a skeleton: a few "bones" - here, guides - drive the motion of the whole. Instead of simulating the many guides that generated the hair, you simulate just a few external guides and let them carry the dense groom along, saving a great deal of time and effort.

 

How it works 

You provide a sparse set of guides whose shape roughly matches the dense hair you want to animate. The operator binds the dense hair to those guides, so as the external guides move - through simulation, animation, or a cache - the dense groom follows. The closer the external guides match the form of the hair, the better the result.

 

Why use it 

• Speed: simulating a handful of guides is far cheaper than simulating full-density hair.
• Control: you can animate or simulate the driving guides independently and predictably.
• Pipeline fit: the driving guides can come from another tool or a cache.

 

Workflow 

1. Prepare a sparse set of guides that approximate your dense groom.
2. Animate or simulate those guides, or load them from a cache.
3. Add Adopt External Guides so the dense hair follows them.

 

Following turning guides 

When the external guides turn, for example a simulated strand swinging over, following only the movement of the guide points shrinks and shears hair that is curlier or longer than its guides.

• Rotation Amount: how much the hair also turns with the guide segments it is bound to. At 100% the hair keeps its length and shape as the guides turn. New Adopt External Guides operators start at 100%; grooms saved earlier keep 0%.
• Match By Length: binds each hair point to the guide point at the same fraction of the strand length instead of the point count.
• Preserve Shape: relaxes the deformed hair back to its original segment lengths and bend, roots fixed. Preserve Shape Iterations sets the number of passes, Preserve Shape Bend Stiffness how strongly the bend comes back.

 

Related 

• Moov Physics Operator - simulate the driving guides.
• Animation Cache Operator - play driving guides back from a cache.
• Hair and Guides - the guide-and-hair relationship this builds on.

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