> simulations

Hair

simulations/hair·v1.5.1

IN:1 OUT:1

SUMMARY

The Hair operator turns every strand of the input into a rod with a frame per segment, holding each segment at its rest length and each joint at its rest bend and twist, so curls and twists keep their shape. Each strand is solved from root to tip in sequence, and the output is the same strands with their points moved.

Roots are pinned by default and ride an animated scalp with Match Animation, while a grabber, per-point falloff attributes, normal and tangent drag, self collision and ground, box, mesh and field colliders shape the motion. The simulation runs as a feedback loop (Initialize, Start, Play) with a Target Feedback Loop POP for forces downstream.

PARAMETERS

PAGEHair

Target Feedback Loop POP	Targetpop	A reference to a POP node downstream in the network whose data is retrieved one frame later. P, PartVel and PartForce are read back.
Time Scale	Timescale	Speed multiplier on the time step. 0 freezes and 2 doubles.
Time Step	Timestep	The time step per frame in seconds, 1 divided by the cook rate (read-only). Time Scale multiplies it.
Substeps	Substeps	Number of solver substeps per 1/60 second. More substeps are more stable.
Iterations	Iterations	Number of constraint passes per substep.
Rebuild Constraints	Rebuildconstraints	Rebuilds the constraints and rest state from the input.
Auto Rebuild	Autorebuild	When on, the constraints are rebuilt every frame, for an animated input or changing topology.
Constraints Built	Constraintsbuilt	Number of constraints made by the last build (read-only).
Build Time (ms)	Buildtime	Duration of the last build in milliseconds (read-only).
Display Constraints	Displayconstraints	Display the constraints.
Initialize	Initializepulse	Initializes the POP from its input and parameters.
Start	Startpulse	Start the simulation from the initialized state.
Play	Play	Pause or play the feedback loop.
Step	Steppulse	Advance the simulation by one frame while paused.

PAGEConstraints

[+]Mass	Mass	Determines the mass: the input Mass unchanged, one set value, or computed from Density by length.
Point Mass	Setmass	Mass of every point when Mass is Set, in kg with 1 unit equal to 1 m.
Density	Density	Mass per unit length when Mass is set to Density.
[+]Thickness	Thickness	Determines the collision radius: the input PointScale, a set value, or the mean segment length times a scale.
Set Thickness	Setthickness	Contact radius of every point when Thickness is Set.
Segment Length Scale	Segmentlengthscale	Sets the self-collision radius as a fraction of the mean segment length, used when Thickness is Segment Length.
[+]Stiffness Scale	Stretchstiffscale	Multiplier on Stiffness. The XPBD compliance is its inverse.
Stiffness	Stretchstiff	Sets the stretch stiffness, multiplied by Stiffness Scale.
Stiffness Attribute	Stretchstiffattr	Point attribute that multiplies the stretch stiffness.
Damping Ratio	Stretchdamp	Sets the damping ratio, where 0 is no damping and 1 is critical damping.
Rest Length Scale	Stretchrestscale	Scales the rest length. Values below 1 shrink it and values above 1 grow it.
Rest Length Attribute	Stretchrestattr	Point attribute that scales the rest length.
[+]Point Promotion	Stretchpromote	Determines how the point values combine into one value per constraint: Average, Minimum, Maximum or Multiply.
[+]Attribute Mode	Stretchattrmode	Determines how the attribute is applied: Multiply or Logarithmic.
Attribute Range	Stretchattrrange	Sets how many decades of stiffness the attribute spans in Logarithmic mode.
[+]Stiffness Scale	Bendstiffscale	Multiplier on Stiffness. The XPBD compliance is its inverse.
Stiffness	Bendstiff	Sets the bend stiffness, multiplied by Stiffness Scale.
Stiffness Attribute	Bendstiffattr	Point attribute that multiplies the bend stiffness.
Damping Ratio	Benddamp	Sets the damping ratio, where 0 is no damping and 1 is critical damping.
Rest Angle Scale	Bendrestscale	Scales the rest angle. 0 makes the rest shape straight.
Rest Angle Attribute	Bendrestattr	Point attribute that scales the rest angle.
[+]Point Promotion	Bendpromote	Determines how the point values combine into one value per constraint: Average, Minimum, Maximum or Multiply.
[+]Attribute Mode	Bendattrmode	Determines how the attribute is applied: Multiply or Logarithmic.
Attribute Range	Bendattrrange	Sets how many decades of stiffness the attribute spans in Logarithmic mode.
Pin First Vertex	Pinroots	Pin the first point of every strand so the hair grows from its root.
Pin Second Vertex	Pinsecond	Also pin the second point. This fixes the root direction so the hair leaves the skin as combed.
Pin Group	Pingroup	Point group of the input to pin.
Match Animation	Matchanimation	When on, pinned points follow the live input. When off, they hold the rest pose.
Display Pins	Displaypins	Display the pinned points.

PAGECollisions

Enable Self Collision	Enableselfcollision	Enable collisions of the points with each other.
Collision Passes	Selfcollisionpasses	Number of self-collision solves per substep.
Stiffness	Selfstiffness	Fraction of each self-collision correction that is applied, from 0 to 1.
Enable Ground Collision	Enablegroundcollision	Collide with an infinite ground plane.
Display Ground	Displayground	Display the ground plane.
[+]Ground Position	Groundposition	A point on the ground plane.
[+]Ground Direction	Grounddirection	Normal of the ground plane. 0 1 0 is a level floor.
Ground Collision Margin	Groundmargin	Distance the points keep from the ground.
Enable Bounding Box Collision	Enablebboxcollision	Keep the points inside the bounding box.
Display Bounding Box	Displaybbox	Enable drawing the bounding box.
[+]Bounding Box Center	Bboxcenter	Center of the bounding box, in collider space.
[+]Bounding Box Size	Bboxsize	Size of the bounding box, in collider space.
Lower Bounds	Bboxlowerbounds	Enable the lower walls of the bounding box in each axis.
Upper Bounds	Bboxupperbounds	Enable the upper walls of the bounding box per axis.
Bounding Box Collision Margin	Bboxmargin	Distance the points keep from the box walls.
Bounding Box POP	Bbox	Optional POP whose world bounds replace the built-in box.
[+]Collision Type	Collisiontype	Selects the collider: none, a POP mesh (ray traced, Windows only) or a field used as an SDF volume.
Display Geometry	Displaygeo	Enable drawing the collider, as the mesh or the field's zero surface.
Collision Passes	Geocollisionpasses	Number of collider solves per substep. More passes hold fast moving geometry.
Collision POP	Collisionpop	The collider, either a mesh POP or an SDF field volume.
[+]Dist Attribute (SDF)	Distattr	For a field collider, the signed distance attribute of the Collision POP, negative inside.
Solid	Solid	When on, points inside the collider are pushed out. When off, the collider is hollow.
Keep Inside	Keepinside	When on, the collider is hollow and every outside point is pulled back in. When off, only escaping points are caught.
Project	Project	Place every point on the collider surface instead of colliding.
Collision Offset	Collisionoffset	Distance the points keep from the collider surface.
Collision Damping	Collisiondamping	Velocity lost on contact. 0 bounces and 1 stops.
[+]Transform Order	Xord	Sets the transform order of the collider and the bounding box.
[+]Rotate Order	Rord	Sets the order of the rotations of the collider and the bounding box.
[+]Translate	T	Translate the collider and the bounding box in the three axes.
[+]Rotate	R	Rotate the collider and the bounding box around the X, Y and Z axes. Angles are given in degrees.
[+]Scale	S	Scale factor for each axis of the collider and the bounding box.
[+]Pivot	P	The pivot point for the rotate and scale of the collider and the bounding box.
Uniform Scale	Scale	Specifies a uniform scale factor for the collider and the bounding box.
[+]Display Color	Displaycolor	Sets the color of the displayed guides.

PAGEForces

[+]Gravity	Gravity	The gravity vector in units per second squared.
Gravity Multiplier	Gravitymultiplier	Multiplies the Gravity vector.
[+]Wind Direction	Winddirection	The direction the wind blows in. Its length does not matter.
Wind Speed	Windspeed	The wind acceleration along Wind Direction, in units per second squared.
Velocity Damping	Velocitydamping	Amount of damping applied to the velocity. 0 applies no damping.
Normal Drag	Normaldrag	Air drag across the strand, per second.
Tangent Drag	Tangentdrag	Air drag along the strand, per second.
Static Threshold	Staticthreshold	Sets the static friction coefficient. Contacts below it grip.
Dynamic Scale	Dynamicscale	Sets the kinetic friction coefficient that slows sliding contacts.
Enable Self	Enableself	Enable friction on the self-collision contacts.
Enable External	Enableexternal	Enable friction on the bounding box, the Collision POP and fields. The ground always uses its own friction.
Ground Static Scale	Groundstaticscale	Sets the static friction of the ground plane. 0 is frictionless.
Ground Dynamic Scale	Grounddynamicscale	Sets the kinetic friction of the ground plane.
Enable Grabber	Enablegrabber	Enable the grabber: grab and drag the simulated points inside a sphere.
Grab	Grab	While on, the points inside the grabber when it turned on follow Position.
[+]Position	Grabposition	Sets the position of the grabber in world space.
[+]Radius	Grabradius	Sets the radius of the grabber sphere on each axis.
Strength	Grabstrength	Determines how firmly the grabbed points follow. 1 holds them like pins, lower values let the simulation pull them.
Transition Range	Transitionrange	Width of the falloff at the edge of the grabber sphere.
Transition Align	Transitionalign	Moves the falloff inside (-0.5) or outside (0.5) the sphere edge.
[+]Transition Type	Transitiontype	Determines the interpolation curve of the falloff.
Display Grabber	Displaygrabber	Display the grabber sphere in the viewport.
Visualize Grabbed Points	Visgrabbedpoints	Color the points the grabber holds (or would take) red.

PAGEAdvanced

[+]Integration Order	Integrationorder	Sets the integration order of the position update.
Enable Max Acceleration	Enablemaxacc	Limit the acceleration to Max Acceleration.
Max Acceleration	Maxacceleration	Sets the maximum acceleration magnitude.
Limit Acceleration in Velocity Update	Limitaccel	When on, the acceleration limit applies to the velocity update instead of the position step.
Fallback to First Order Integration on Collision	Fallbackcollision	Use first order integration on collision, which is more stable.
Relaxation	Relaxation	Scales each constraint step. 1 is exact, below 1 is softer, above 1 is stiffer but jittery.
Self Step Clamp	Selfclampscale	Limits the move per substep to this fraction of the contact diameter, which prevents tunneling.
Rest Exclude Scale	Restexcludescale	Skips self-collision pairs that are closer at rest than this multiple of the contact distance.

PAGECommon

Free Extra GPU Memory

Freeextragpumem

Free memory that has accumulated when output memory has grown and shrunk.

INPUTS

Input 0 POP - Geometry

OUTPUTS

Output 0 POP - Geometry