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POP Metball Force dynamics node

A POP node that applies forces according to metaballs.

On this page

Using Metaball Force
Parameters
- Parameters
- Bindings
Inputs
Outputs
Locals

The POP Metaball Force node applies a force to particles according to how close they are to metaballs.

The metaballs must be set up with force attributes using the Force SOP. Particles within range of the metaballs will be influenced by them, scaled by the weight of the metaball.

This operator modifies the force attribute.

Using Metaball Force

Create some metaballs using the Metaball shelf tool.
Create a particle system using the Location or Source shelf tools.
Click the Metaball Force tool on the Particles tab.
Select the metaballs you want to affect your particles and press Enter.

You can set the Force Scale parameter on the Metaball Force node to either attract or repel particles. A positive value will attract particles and a negative value will repel particles.

By default, this tool applies a Radial Force, which can be changed to Directional Force on the Force SOP. There are also force controls for axial, vortex, and spiral forces.

The following example shows the metaballs repelling the particles.

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.

Guide

Controls if the guide geometry for this node should be shown.

Note

Even if it is enabled here, it can also be disabled by using the Hidden flag on the DOP Node.

Parameters

Geometry Source

Specifies the geometry to use.

Use Parameter Values

Use the SOP specified in the SOP Path parameter.

Use DOP Object

Use the named DOP object in this DOP network.

Use First Context Geometry

Use the SOP connected to the DOP network’s first input.

Use Second Context Geometry

Use the SOP connected to the DOP network’s second input.

Use Third Context Geometry

Use the SOP connected to the DOP network’s third input.

Use Fourth Context Geometry

Use the SOP connected to the DOP network’s fourth input.

SOP Path

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

DOP Objects

Name of DOP Objects (When Geometry Source is set to Use DOP Object).

Force Scale

The metaball’s force scales will be scaled by this factor, which allows you to then have different particles react differently. A positive value will attract particles and a negative value will repel particles.

Ignore Mass

Ignores any mass on the input particles.

Since forces are stored as force rather than accel (acceleration), this is done by multiplying the force by the mass attribute. This will then be canceled out by the solver.

airresist will also be similarly multiplied.

Ignoring mass ensures that small pieces of an RBD object move at the same speed as big pieces. This makes for a more controllable simulation.

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 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