Houdini 17.0 Nodes Dynamics nodes

Voronoi Fracture Parameters dynamics node

Defines the parameters for dynamic fracturing using the Voronoi Fracture Solver

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Parameters

Impact

Parameters on this tab control when the object to which this data is applied can fracture.

Impact Group

An impact with objects in the specified group can potentially cause this object to fracture.

Min/Max Impact

The minimum impact impulse that can cause this object to fracture. Any impact over the minimum can cause a fracture; the range is used in conjunction with the Radius Scale parameter, allowing heavier impacts to map to a larger impact radius.

The minimum impact gets mapped to the minimum impact radius scale, and the maximum impact force gets mapped to the maximum impact scale. Having a maximum ensures that values are clipped so that really strong impacts from creating huge impact zone.

Minimum Volume

The minimum volume an object must have to be eligible for fracturing. The object’s volume is calculated by dividing its mass by its density.

Note

This volume only work this way if you turn on Compute Mass on your RBD Objects. If you don’t, the volume will not be what you expect and you may have to just set it to 0.

Re-fracture Delay

The interval (in seconds of simulation time) after an object fractures before it can be eligible for fracturing again.

Fracture From Magnet Force Metaballs

Use the metaball geometry associated with any Magnet Forces applied to the object as a source for potential fracturing. This can be used to cause explosion-type effects, where the magnet force itself causes the fracture.

Minimum Magnet Volume

The minimum ratio of the object’s collision volume that must be overlapped by the magnet metaball before fracturing can occur. It can be useful to delay the fracturing until the metaball overlaps much of the object’s volume when using animated metaball geometry.

Maximum Fractures

Controls how many times the object can break. A maximum fracture of 1 will break on the first impact, but the resulting pieces won’t break again. A maximum fracture of 2 will allow all the pieces from the first fracture to break.

Note

When some pieces break off the main chunk, the main chunk is still considered a "piece", which means it will lose one of its max fractures.

Impact Radius

The radius of the metaball to be copied to each impact point.

Min/Max Scale

Scale the impact radius by this amount, based upon the ranges specified in the Minimum Impact parameter. Radius scale multiplies the Impact Radius gives you the size of metaball around each impact point. So given a single point of impact, it is roughly your crater radius. There are two values for the min/max.

Points

Parameters on this tab control the generation of fracture points from the eligible impacts. See the Voronoi Fracture Points SOP help for more information.

Compute Number of Fracture Points

Calculates the number of points to scatter in each fracture region based on its surface area.

Points Per Area

The number of points per unit of surface area. This can be scaled by the Point Density parameter for each region.

Number of Points

The number of points to generate.

Per Impact

Whether the Number of Points parameter specifies the total number of generated points or the number of generated points for each impact point.

Show Fracture Points

Displays the generated points. Yellow is for the surface region, red for the interior, and blue for the exterior.

Surface

Point Density

The density of point generation for this region. If Compute Number Of Points is enabled, this parameter is a multiplier of the Points Per Area value. If an explicit Number of Points value is being used, this parameter determines the proportion of those points allocated to this region.

Surface Offset

The amount to offset the generated points from the object surface. Offsetting by a small amount can cause smaller, more debris-like fractured pieces from the Surface region.

Radius Scale

The amount to scale the impact radius before calculating the Surface region.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

Interior

Point Density

The density of point generation for this region. If Compute Number Of Points is enabled, this parameter is a multiplier of the Points Per Area value. If an explicit Number of Points value is being used, this parameter determines the proportion of those points allocated to this region.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

Exterior

Point Density

The density of point generation for this region. If Compute Number Of Points is enabled, this parameter is a multiplier of the Points Per Area value. If an explicit Number of Points value is being used, this parameter determines the proportion of those points allocated to this region.

Scatter Location

At Impact

Scatter points at the boundary of the Interior and Exterior regions.

Exterior Volume

Scatter points throughout the exterior volume.

Both

Scatter points at both of the above locations.

Impact Offset

The offset of the Interior / Exterior boundary when scattering using the At Impact or Both setting above.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

Fracture

Parameters on this tab control the fracturing of the geometry from the generated fracture points. See the Voronoi Fracture SOP help for more information.

/nodes/sop/voronoifracture#cuspnormals /nodes/sop/voronoifracture#cuspangle /nodes/sop/voronoifracture#cuspouternormals /nodes/sop/voronoifracture#cuspouterangle

Cut

Cut Plane Offset

Offsets the cut plane between adjacent cell points before cutting. Increasing this has the effect of putting space between each fractured piece.

Note

Setting this parameter to a non-zero value disables Clustering.

Cluster

Cluster Pieces

Fuse the individual pieces into larger clusters based on their input points sharing a common, non-zero cluster attribute value. Values for this attribute can come from the generated fracture points, or from noise as specified below.

Size

The size of the cells for the noise added to the input points. This roughly corresponds to the size of the clusters.

Offset

The offset of the cellular noise added to the interior points.

Jitter

The jitter of the cellular noise added to the interior points.

Random Detachment

Randomly detach pieces from clusters.

Detach Seed

The random seed used for detachment.

Detach Ratio

The probability that a particular piece will be detached.

Interior Detail

Add Interior Detail

Adds additional polygons to the interior surfaces of pieces.

Detail Size

The size of the polygons added to the interior surfaces.

Noise Type

The type of noise added to the interior points.

Frequency

The frequency of the noise added to the interior points.

Offset

The offset of the noise added to the interior points.

Turbulence

The turbulence of the noise added to the interior points.

Depth / Noise Scale Bias

The value for the bias curve that maps depth within the surface to the amplitude of the noise applied.

Velocity Transfer

Parameters on this tab control how velocity is transferred from the intact object to the fractured pieces at the time of impact. Fractured pieces can inherit velocity from the intact object’s pre- and post-impact velocity. At the time of fracture, a velocity impulse is also calculated for each fracturing impact, and is added to the pieces' point velocities with a user-specified strength and falloff. This impulse can add velocity to the pieces even when the intact object has no velocity before or after impact.

Pre/Post Velocity Bias

The amount of pre- or post-impact velocity that the fractured pieces should inherit.

Setting this to a low value (biased towards pre-impact velocity) makes the pieces inherit little of the object’s collision response, and the object will appear brittle, with little internal strength.

Setting this to a high value (biased towards post-impact velocity) causes the pieces to inherit much of the object’s collision response, and the object will appear harder, with more internal strength.

Impulse Distance

The distance over which the velocity impulse falls off from each impact. The impulse will have no effect past this distance.

Radial Impulse Scale

A scale for the radial component of the velocity impulse. Increasing this value will give velocity in an outwards direction from the fracturing impacts to the pieces within the Impulse Distance.

Normal Impulse Scale

A scale for the normal component of the velocity impulse. Increasing this value will give velocity (in the direction of the collision response) to the pieces within the Impulse Distance, even if the velocity bias for the entire object is towards pre-impact velocities.

Parameter Operations

Each data option parameter has an associated menu which specifies how that parameter operates.

Use Default

Use the value from the Default Operation menu.

Set Initial

Set the value of this parameter only when this data is created. On all subsequent timesteps, the value of this parameter is not altered. This is useful for setting up initial conditions like position and velocity.

Set Always

Always set the value of this parameter. This is useful when specific keyframed values are required over time. This could be used to keyframe the position of an object over time, or to cause the geometry from a SOP to be refetched at each timestep if the geometry is deforming.

You can also use this setting in conjunction with the local variables for a parameter value to modify a value over time. For example, in the X Position, an expression like $tx + 0.1 would cause the object to move 0.1 units to the right on each timestep.

Set Never

Do not ever set the value of this parameter. This option is most useful when using this node to modify an existing piece of data connected through the first input.

For example, an RBD State DOP may want to animate just the mass of an object, and nothing else. The Set Never option could be used on all parameters except for Mass, which would use Set Always.

Default Operation

For any parameters with their Operation menu set to Use Default, this parameter controls what operation is used.

This parameter has the same menu options and meanings as the Parameter Operations menus, but without the Use Default choice.

Data Sharing

Controls the way in which the data created by this node is shared among multiple objects in the simulation.

Data sharing can greatly reduce the memory footprint of a simulation, but at the expense of requiring all objects to have exactly the same data associated with them.

Do Not Share Data

No data sharing is used. Each object has its own copy of the data attached.

This is appropriate for situations where the data needs to be customized on a per-object basis, such as setting up initial positions and velocities for objects.

Share Data Across All Time

This node only creates a single piece of data for the whole simulation. This data is created the first time it is needed, so any expressions will be evaluated only for the first object.

All subsequent objects will have the data attached with the same values that were calculated from the expressions for the first object. It is important to note that expressions are not stored with the data, so they cannot be evaluated after the data is created.

Expressions are evaluated by the DOP node before creating the data. Expressions involving time will also only be evaluated when this single piece of data is created. This option is appropriate for data that does not change over time, and is the same for all objects, such as a Gravity DOP.

Share Data In One Timestep

A new piece of data is created for each timestep in the simulation. Within a timestep though, all objects have the same data attached to them. So expressions involving time will cause this data to animate over time, but expressions involving the object will only evaluate for the first object to which the data is attached.

This option is appropriate for data that changes over time, but is the same for all objects such as a Fan Force DOP, where the fan may move or rotate over time.

Activation

Determines if this node should do anything on a given timestep and for a particular object. If this parameter is an expression, it is evaluated for each object (even if data sharing is turned on).

If it evaluates to a non-zero value, then the data is attached to that object. If it evaluates to zero, no data is attached, and data previously attached by this node is removed.

Group

When an object connector is attached to the first input of this node, this parameter can be used to choose a subset of those objects to be affected by this node.

Data Name

Indicates the name that should be used to attach the data to an object or other piece of data. If the Data Name contains a "/" (or several), that indicates traversing inside subdata.

For example, if the Fan Force DOP has the default Data Name "Forces/Fan". This attaches the data with the name "Fan" to an existing piece of data named "Forces". If no data named "Forces" exists, a simple piece of container data is created to hold the "Fan" subdata.

Different pieces of data have different requirements on what names should be used for them. Except in very rare situations, the default value should be used. Some exceptions are described with particular pieces of data or with solvers that make use of some particular type of data.

Unique Data Name

Turning on this parameter modifies the Data Name parameter value to ensure that the data created by this node is attached with a unique name so it will not overwrite any existing data.

With this parameter turned off, attaching two pieces of data with the same name will cause the second one to replace the first. There are situations where each type of behavior is desirable.

If an object needs to have several Fan Forces blowing on it, it is much easier to use the Unique Data Name feature to ensure that each fan does not overwrite a previous fan rather than trying to change the Data Name of each fan individually to avoid conflicts.

On the other hand, if an object is known to have RBD State data already attached to it, leaving this option turned off will allow some new RBD State data to overwrite the existing data.

Inputs

First Input

This optional input can be used to control which simulation objects are modified by this node. Any objects connected through this input and which match the Group parameter field will be modified.

If this input is not connected, this node can be used in conjunction with an Apply Data node, or can be used as an input to another data node.

All Other Inputs

If this node has more input connectors, other data nodes can be attached to act as modifiers for the data created by this node.

The specific types of subdata that are meaningful vary from node to node. Click an input connector to see a list of available data nodes that can be meaningfully attached.

Outputs

First Output

The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).

If no object stream is connected to this node, the output is a data output. This data output can be connected to an Apply Data DOP, or connected directly to a data input of another data node, to attach the data from this node to an object or another piece of data.

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

This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).

In this case, this value is set to the name of the relationship the data to which the data is being attached.

RELOBJIDS

This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).

In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affected Objects of the relationship to which the data is being attached.

RELOBJNAMES

This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).

In this case, this value is set to a string that is a space separated list of the names of all the Affected Objects of the relationship to which the data is being attached.

RELAFFOBJIDS

This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).

In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affector Objects of the relationship to which the data is being attached.

RELAFFOBJNAMES

This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).

In this case, this value is set to a string that is a space separated list of the names of all the Affector Objects of the relationship to which the data is being attached.

ST

This value is the simulation time for which the node is being evaluated.

This value may not be equal to the current Houdini time represented by the variable T, depending on the settings of the DOP Network Offset Time and Time Scale parameters.

This value is guaranteed to have a value of zero at the start of a simulation, so when testing for the first timestep of a simulation, it is best to use a test like $ST == 0 rather than $T == 0 or $FF == 1.

SF

This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.

This value may not be equal to the current Houdini frame number represented by the variable F, depending on the settings of the DOP Network parameters. Instead, this value is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).

TIMESTEP

This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.

SFPS

This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.

SNOBJ

This is the number of objects in the simulation. For nodes that create objects such as the Empty Object node, this value will increase for each object that is evaluated.

A good way to guarantee unique object names is to use an expression like object_$SNOBJ.

NOBJ

This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.

This value may return 0 if the node does not process each object sequentially (such as the Group DOP).

OBJ

This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just the object’s position in the current order of processing.

This value is useful for generating a random number for each object, or simply splitting the objects into two or more groups to be processed in different ways. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

OBJID

This is the unique object identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused.

The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.

This value is also the best way to look up information on an object using the dopfield expression function. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

ALLOBJIDS

This string contains a space separated list of the unique object identifiers for every object being processed by the current node.

ALLOBJNAMES

This string contains a space separated list of the names of every object being processed by the current node.

OBJCT

This value is the simulation time (see variable ST) at which the current object was created.

Therefore, to check if an object was created on the current timestep, the expression $ST == $OBJCT should always be used. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJCF

This value is the simulation frame (see variable SF) at which the current object was created.

This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJNAME

This is a string value containing the name of the object being processed.

Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.

The object name can also be used to treat a number of similar objects (with the same name) as a virtual group. If there are 20 objects named "myobject", specifying strcmp($OBJNAME, "myobject") == 0 in the activation field of a DOP will cause that DOP to operate only on those 20 objects. This value will be the empty string if the node does not process objects sequentially (such as the Group DOP).

DOPNET

This is a string value containing the full path of the current DOP Network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP Network that contains the node.

Note

Most dynamics nodes have local variables with the same names as the node’s parameters. For example, in a Position node, you could write the expression:

$tx + 0.1

…to make the object move 0.1 units along the X axis at each timestep.

Examples

The following examples include this node.

FractureExamples Example for Voronoi Fracture Solver dynamics node

This example actually includes eight examples of ways that you can use voronoi fracturing in Houdini. In particular, it shows how you can use the Voronoi Fracture Solver and the Voronoi Fracture Configure Object nodes in your fracture simulations. Turn on the display flags for these examples one at a time to play the animation and dive down into each example to examine the setup.

See also

Dynamics nodes