Soft Body particle node

Performs soft body deformations similar to the Spring SOP.

All

Parameters

Local variables

Example files

The Softbody POP performs soft body deformations similar to the Spring SOP. The edges of the geometry act as “springs”, which pull the points back toward their original shape.

When this operator is first activated, the geometry at that time is used. If the SOP changes thereafter, those changes will not be reflected in the geometry produced by the POP network.

The POP creates a new particle system that will move the points of the geometry. To make this particle system invisible to the scene, enable the Hide Particle System parameter. In the info pop-up, the particle system will be denoted as “virtual”.

For more stable behavior, see the Squishy Object in DOPs.

Parameters

Activation

Turns the POP on and off.

Source

Geometry Source

Specifies the SOP to use.

Use Parameter Values	Use the SOP specified in the SOP parameter below.
Use First Context Geometry	Use the SOP connected to the POP network’s first input.
Use Second Context Geometry	Use the SOP connected to the POP network’s second input.
Use Third Context Geometry	Use the SOP connected to the POP network’s third input.
Use Fourth Context Geometry	Use the SOP connected to the POP network’s fourth input.

SOP

Path to the SOP (when Geometry source is set to Use Parameter Values).

Ignore Transform Object

Particles normally use the object space of the SOP being cooked. Turn this parameter on to not transform into the space of the cooking SOP.

Fixed Points

Points to be considered stationary.

Fixed Points go to Source Positions

Fixed Points are put to their positions in the Source.

Copy Groups from Source

All Source groups are copied at each frame. Useful if the Fixed Points group contents are animated.

Hide particle system

Make the particle system that controls the softbody deformation hidden (i.e. does not show in scene).

Spring

Spring Behavior

How the springs will behave.

Hooke’s Law	Use Hooke’s law. Force = displacement x spring constant.
Normalize Displacement	Like Hooke’s law except displacement is normalized to the original length of the spring. (Behavior used in Houdini 2.5).
No Springs	No springs will be used.

Spring Constant

Stiffness of the spring.

Initial Tension

Initial spring tension before deformations.

Attributes

Create Local Variables	Create local variables corresponding to inherited attributes.
Add ID Attributes	Add ID and parent attributes.
Add Generation Attribute	Add generation attribute.
Add Origin Attribute	Add origin attribute.
Use as Origin	How to set the origin.
Origin Index	Index as used in origin.
Add Speed Attribute	Add speed attribute (length of velocity vector).

Local variables

Standard POP local variables

AGE	The seconds a particle in the template has been alive.
AX AY AZ	Acceleration of the particle.
BBX BBY BBZ	The point’s relative position in the bounding box.
DEAD	Point is dead.
ITER	Processing iteration number.
JUSTHIT	A collision for this particle was detected (for example, by the Collision POP) during the processing of this timestep (that is, this iteration of the particle simulation). This variable is cleared at the beginning of each timestep. Note that the collision POP actually detects any collisions which would have occurred the during the previous frame.
LIFE	Percent of total life used (from 0 to 1).
LIFESPAN	Expected lifetime of particle.
MAPU MAPV MAPW	Point or vertex texture coordinates.
NPT	Total number of points.
NGRP	Total number of points in source group.
NX NY NZ	Normal vector.
PT	The point number of the currently processed point. The `PT` is not constant like `ID`; it changes based on the number of points.
RESTX RESTY RESTZ	The rest position.
SLIDING	The sliding state of the particle.
SPRINGK	Elasticity of a point.
STOPPED	Point is stopped.
STUCK	1 if particle is stuck to a collision object.
TENSION	Spring tension.
TIMEINC	Time increment.
TX TY TZ	Point position.
U V	Surface UV values.
VX VY VZ	Velocity direction.
WEIGHT	Point spline weight.

Added by Collision POP/Limit POP

DIST	Distance from particle to last collision.
HCR HCG HCB	Diffuse color at the collision point on the surface the particle collided with.
HITID	ID for last collision. You can control how this attribute is set in the Collision or Limit POP to help distinguish types of collisions.
HITTIME	The time at which the last collision occurred.
HMAPU HMAPV	The texture map UV coordinates for the surface location where the last collision occurred.
HNX HNY HNZ	The normal at the surface location where the last collision occurred.
HTX HTY HTZ	World space position of the last collision.
HU HV	The UV coordinates for the surface location where the last collision occurred.
NUMHIT	Number of times the particle has collided.

Added by Color POP

CA	Point or vertex alpha value.
CR CG CB	Diffuse point or vertex color.

Added by Property POP

ATTRACT	Attractor point.
CHARGE	Charge of the particle.
CLING	Point is clinging to geometry.
DRAG	Point drag.
FOLLOW	Leader to follow.
MASS	Point mass.
PSCALE	Particle Scale.
SCALEX SCALEY SCALEZ	Non-uniform scale.

Added by Proximity POP

NEAREST	Either the point number or id of the particle nearest to this one.
NEARESTDIST	The distance to the nearest particle.
NUMPROXIMITY	The number of particles within a specified proximity to this particle.

Added by Rotation POP

ROTA	Rotation angle.
ROTX ROTY ROTZ	Rotation axis.

Added by Source POP

GEN	Generation.
ID	ID number, which always remains constant.
ORIGIN	Original Source point was birthed from.
PARENT	Parent’s ID Number.

Added by Speed Limit POP

SPEEDMAX	Maximum speed.
SPEEDMIN	Minimum speed.

Added by Sprite POP

SROT	Sprite rotation around view axis (in degrees).
STEXU STEXV	Texture coordinate of sprite’s lower-left corner.
STEXW STEXH	Size of sprite in texture space.
SX SY	Sprite scale.

Controlled by Suppress Rule POP

SUPPPOS	Suppress default position rule.
SUPPVEL	Suppress default velocity rule.
SUPPUP	Suppress default up-vector rule.
SUPPAGE	Suppress default aging rule.
SUPPROT	1 if particle is suppressing its default rotation rule.
SUPPANGVEL	1 if particle is suppressing its default angular velocity rule.

Added by Up Vector POP

PVX PVY PVZ	Previous velocity.
UPX UPY UPZ	Up vector.

Added by Location, Source, Softbody, Split POPs

SPEED

Absolute speed of particle.

Example files

SoftBodySheet

$HFS/houdini/help/examples/nodes/pop/softbody/SoftBodySheet.cmd

Load | Launch

This example uses the Softbody POP to deform a SOP geometry to create a cloth-like effect.

It also gives examples of how the Group POP, Force POP, and Drag POP are used to refine the motion of the Softbody animation.

This can be useful in creating things such as fabrics and organic surfaces.

Press Play to see the animation.

Usages in other examples

Example name	Example for