POP Group dynamics node

A POP node that groups particles.

On this page	Parameters Rule Bounding Random Combine Bindings Inputs Outputs Locals
Since	13.0

The POP Group node creates a point group to provide a way to refer to a group of particles later by name.

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

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

Group

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

Group Name

The name of the group to create. If this field is blank, no grouping will be done.

Preserve Group

If the group is preserved, each frame new particles will be added to the group by this POP. Otherwise the group is reset each time.

Rule ¶

Enable

Controls if the rule is active.

VEXpression

A local expression providing a rule for setting up group membership. The ingroup variable should be assigned 1 if the particle should be made part of the group.

Bounding ¶

Enable

Controls if the particles will be grouped by a bounding region.

Bounding Type

The shape of the bounding region.

Bounding Box

A box of the given dimensions.

Bounding Sphere

A sphere of the given dimensions.

Bounding Object

Whether the point is inside the given object.

Bounding Volume

The object’s volume primitive is used to determine if the point is inside.

Center

Center of the bounding primitive.

Size

Size of the bounding primitive. This is a diameter, not radius.

Object Source

The source of the bounding object’s geometry. The context geometry refer to the inputs of this DOP network.

SOP Path

Path to the bounding object.

DOP Object

The name of a DOP object in the same simulation as this.

DOP Data

The subdata path for the geometry in the DOP Object.

Iso Surface

What volume value to threshold between inside and outside.

Invert

Inverts the sense of inside and outside for the group. This is particularly useful with the volume bounding option and switching between a fog volume and an SDF volume.

Random ¶

Enable

Controls if the rule is active.

Behavior

When particles pass the chance test, they will then either be added to the group, or removed, according to this test. Setting to remove allows you to remove points that are added by the previous folders of the group test.

Chance

The probability that any particle will pass this test. 0 means no particles will pass, 1 means all will pass.

Seed

The random seed used for grouping points. The id attribute is added to this implicitly.

Combine ¶

Combines different groups based on boolean operators.

Group

This section allows you to create a new group out of existing groups. Enter the group to operate on or create in the first field and the name of the existing group in the field on the other side of the buttons. You can either include the contents of the other group by selecting

group by selecting Equals all but. Use the fields below to combine additional groups.

Bindings ¶

Geometry

The name of the simulation data to apply the POP node to. This commonly is Geometry, but POP Networks can be designed to apply to different geometry if desired.

Evaluation Node Path

For nodes with local expressions, this controls where ch() style expressions in VEX are evaluated with respect to. By making this ., you can ensure relative references work. It is important to promote this if you are embedding a node inside an HDA if you are also exporting the local expressions.

Inputs ¶

First Input

This optional input has two purposes.

First, if it is wired to other POP nodes, they will be executed prior to this node executing. The chain of nodes will be processed in a top-down manner.

Second, if the input chain has a stream generator (such as POP Location, POP Source, or POP Stream), this node will only operate on the particles in that stream.

Outputs ¶

First Output

The output of this node should be wired into a solver chain.

Merge nodes can be used to combine multiple solver chains.

The final wiring should go into one of the purple inputs of a full-solver, such as POP Solver or FLIP Solver.

Locals ¶

channelname

This DOP node defines a local variable for each channel and parameter on the Data Options page, with the same name as the channel. So for example, the node may have channels for Position (positionx, positiony, positionz) and a parameter for an object name (objectname).

Then there will also be local variables with the names positionx, positiony, positionz, and objectname. These variables will evaluate to the previous value for that parameter.

This previous value is always stored as part of the data attached to the object being processed. This is essentially a shortcut for a dopfield expression like:

dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)

If the data does not already exist, then a value of zero or an empty string will be returned.

DATACT

This value is the simulation time (see variable ST) at which the current data was created. This value may not be the same as the current simulation time if this node is modifying existing data, rather than creating new data.

DATACF

This value is the simulation frame (see variable SF) at which the current data was created. This value may not be the same as the current simulation frame if this node is modifying existing data, rather than creating new data.

RELNAME