Color particle node

Changes a particle’s diffuse color and/or alpha.

All

Parameters

Local variables

Example files

This operator lets you set the color and/or alpha of its input particles by specifying the value directly, via a ramp file, or from a compositing operator.

This operator will add the color (Cd) or alpha (Alpha) attributes to particles if they do not exist already.

Using Color

Select the particle system you want to apply color to.
Click the Color tool on the Drive Particles tab.
Specify the node settings in the operation controls toolbar or parameter editor.

Parameters

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

Color

This tab controls whether and how to set the color of the input particles.

Pass	Do not modify the color.
Param	Set the color to an RGB value.
Ramp	Get the color from a ramp.
COP	Get the color from a compositing operator (an image).

Color: Param

Color

Color to set on the input particles.

Color: Ramp

Lookup

Use the ramp editor to create a color ramp, then use this parameter to control which point along the ramp the particle gets its color from. You can keyframe this parameter or enter an expression.

To remove a color ramp, click a bar and drag it up.

Color: COP

COP Path	Path of a COP to get color from.
U	U Parameter to evaluate COP at.
V	V Parameter to evaluate COP at.

Alpha

This tab controls whether and how to set the alpha (opacity) of the input particles.

Pass	Do not modify the alpha.
Param	Set the alpha to a value.
Ramp	Get the alpha from a ramp.
COP	Get the alpha from a compositing operator (an image).
Speed	Set the alpha according to the particle’s speed.

Alpha: Param

Alpha

Alpha value to set on the input particles.

Alpha: Ramp

Lookup

Use the ramp editor to create an alpha ramp, then use this parameter to control which point along the ramp the particle gets its alpha from. You can keyframe this parameter or enter an expression.

Alpha: COP

COP Path	Path of a COP to get alpha from.
U	U Parameter to evaluate COP at.
V	V Parameter to evaluate COP at.

Alpha: Speed

To set alpha by speed, enter the low speed (corresponding to alpha = 0) and high speed (corresponding to alpha = 1).

Alpha 0 Speed	Speed at which alpha is 0.
Alpha 1 Speed	Speed at which alpha is 1.

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

FromCops

$HFS/houdini/help/examples/nodes/pop/color/FromCops.cmd

Load | Launch

This example shows how COPs can be used to color particles. The particles take on the colors of the butterfly image that is loaded in COPs.

A Color POP is used to color the particles from a COP. It uses the particle’s bounding box X and Y positions as the U and V lookup values in the COP.

HitId

$HFS/houdini/help/examples/nodes/pop/color/HitId.cmd

Load | Launch

This example shows how the Hit ID attribute can be used to determine which collision object a particle hit last. After a particle bounces off a grid, its color is changed according to the ID of the collision object.

Essentially, there are four collision objects. When a particle hits the collision object, it bounces and its “hitid” attribute is set to a value dependent on which object it hit. The value is specified by the “Hit Index” parameter in the Behvior tab of the Collision POP.

The Color POP is then applied to set the color based on which object the particle hit last. The lookup value is based on the $HITID variable.

Usages in other examples

Example name	Example for
HitColor	Collision particle node	Load \| Launch
BounceSplit	Collision particle node	Load \| Launch
OrbitAlternate	Orbit particle node	Load \| Launch
Fetch	Fetch particle node	Load \| Launch
SplitSelf	Split particle node	Load \| Launch
SparksStream	Stream particle node	Load \| Launch
SoftBodySheet	Soft Body particle node	Load \| Launch
Swarm	Property particle node	Load \| Launch