Creep particle node

Causes particles to stick to geometry.

All

Parameters

Local variables

Example files

This operator forces the input particles to stay on a surface. It also lets you control the U/V position of the particles on the surface to make them creep across the surface. It allows you to set the position of the particles explicitly at every frame using the U/V position.

This operator affects the following attributes: pstate (uniform scale), posprim (number of the primitive to stick to within the referenced SOP), and posuv (U/V position of particle on the primitive).

Using Creep

Select the particle system you want to be affected.
Click the Creep tool on the Drive Particles tab.
Select the object you want the particles to stick to or slide along and press Enter to confirm your selection.

The behavior can be modified in the parameter editor.

Parameters

Activation

Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.

Note that this is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.

Source Group

Only affect a group of points (created with, for example, a Group POP or Collision POP) out of all the points in the input.

Behavior

How the input particles behave on the surface.

Stick	Particles stay at the UV coordinates specified below.
Slide	Particles slide along the surface as they are affected by forces.

Stuck

If this value is 1 (or greater than one), a particle that would otherwise slide will be stuck. Use an expression here to decide which particles are stuck to the surface.

Geometry Source

Specifies the SOP to stick to.

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 to stick to (when Geometry Source is set to Use parameter values).

Prim Number

The number of the primitive to stick to within the referenced SOP.

Prim U/V

U/V position of particle on the primitive.

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

CreepFromCenter

$HFS/houdini/help/examples/nodes/pop/creep/CreepFromCenter.cmd

Load | Launch

This is a very basic example of how the Creep POP is used to slide particles on the surface of some geometry starting from its parametric center.

CreepSlide

$HFS/houdini/help/examples/nodes/pop/creep/CreepSlide.cmd

Load | Launch

This example demonstrates the Slide behavior of the Creep POP. Particles are moved across a deformed surface using a Force POP to drive the Creep POPs slide function.

SimpleCreep

$HFS/houdini/help/examples/nodes/pop/creep/SimpleCreep.cmd

Load | Launch

This is a very basic example of how the Creep POP is used to stick particles on the surface of some geometry.

Usages in other examples

Example name	Example for