Adds custom attributes to particles.
This operator can add float, integer, or vector user attributes to the input particles. After you add a user attribute, you can use it anywhere local variables are allowed.
If you do not specify a Local Variable name, Houdini will use the
attribute name (converted to uppercase). Because Houdini allows the
creation of attribute arrays, the local variable name ends up being the
attribute name followed by an index (even if the attribute created is
not an array). So, if you create an attribute foo, the local variable
will be FOO1.
For example, Vector attribute “abc” will create local variables $ABCX,
$ABCY, and $ABCZ. Float attribute “abc” of size 2 will create the
local $ABC1 and $ABC2.
The Attribute POP allows you to both create and reset attributes. Since we know that an attribute called foo maps to $FOO1, you can just recreate $FOO1 with another Attribute POP.
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. |
| Name | Name of the attribute to create/set. |
| Local Variable | Name of the corresponding local variable. Houdini will convert this name to uppercase for consistency with built-in locals. |
| Type | The type of value the attribute can hold: Float, Integer or Vector. |
| Size | An attribute can hold an array of values. To create an array, set this parameter to the number of elements in the array. |
| Default | Default value for the attribute. |
| Write Values | Disabling the writing of values prevents the Attribute POP from changing the attributes. This is useful if you merely want to ensure the attribute exists but want to preserve any existing values. |
| Value | Value to set attribute to. |
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 |
| 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. |
Examples that use this node
| Example for | Example name | |
|---|---|---|
| Particle Fluid Object | PopFlow | Load | Launch |
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| Particle Fluid Solver | PopFlow | Load | Launch |
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| Color | ColorNumhit | Load | Launch |
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