Houdini 17.0 Nodes Dynamics nodes

Static Solver dynamics node

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The Static Solver DOP is a solver which does nothing to its objects at each timestep. Although the behavior of the object is the same as if no solver was attached to the object, it can be necessary to use this solver when using a Switch Solver or Blend Solver. When using those solvers, there is no way to turn off solving other than using this Static Solver.

Parameters

Make Objects Mutual Affectors

All objects connected to the first input of this node become mutual affectors.

This is equivalent to using an Affector DOP to create an affector relationship between * and * before connecting it to this node. This option makes it convenient to have all objects feeding into a solver node affect each other.

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.

ApplyRelationship Example for Apply Relationship dynamics node

This example shows how you can use the Apply Relationship DOP to add pin constraints to wire objects.

BridgeCollapse Example for Apply Relationship dynamics node

This example shows how to use the Apply Relationship DOP to propagate constraints automatically and create an RBD simulation of a collapsing bridge.

ClothAttachedDynamic Example for Cloth Object dynamics node

This example shows a piece of cloth attached to a dynamics point on a rigid object.

ClothFriction Example for Cloth Object dynamics node

This cloth example demonstrates the Friction parameter on the Physical properties of a cloth object.

MultipleSphereClothCollisions Example for Cloth Object dynamics node

This example shows a pieces of cloth with different properties colliding with spheres. By adjusting the stiffness, bend, and surfacemassdensity values, we can give the cloth a variety of different behaviours.

PanelledClothRuffles Example for Cloth Object dynamics node

This example demonstraits a paneling workflow and use of the seamangle primitive attribute to create a cloth ruffle attached to a static object.

AnchorPins Example for Constraint Network dynamics node

This example demonstrates how different anchor positions can affect pin constraints.

AngularMotorDenting Example for Constraint Network dynamics node

This example demonstrates how angular motors can be used with pin constraints to create a denting effect.

BreakingSprings Example for Constraint Network dynamics node

This example shows how to use a SOP Solver to break spring constraints in a constraint network that have stretched too far.

Chains Example for Constraint Network dynamics node

This example shows how to create a chain of objects that are connected together by pin constraints.

ControlledGlueBreaking Example for Constraint Network dynamics node

This example shows how to gradually remove glue bonds from a constraint network and control the crumbling of a building.

GlueConstraintNetwork Example for Constraint Network dynamics node

This example shows how to create a constraint network to glue together adjacent pieces of a fractured object. It also shows how primitive attributes such as 'strength' can be used to modify properties of individual constraints in the network.

Hinges Example for Constraint Network dynamics node

This example demonstrates how to use pin constraints to create hinges between objects.

SpringToGlue Example for Constraint Network dynamics node

This example shows how to create spring constraints between nearby objects, and then change those constraints to glue constraints during the simulation.

CrowdHeightField Example for Crowd Solver dynamics node

This example demonstrates using heightfields for terrain adaptation in the crowd solver, and for collisions against ragdolls in the Bullet solver.

PinnedRagdolls Example for Crowd Solver dynamics node

This example demonstrates how to set up constraints to attach a ragdoll to an external object, and how to use motors to drive an active ragdoll with an animation clip.

CrowdTriggers Example for Crowd Trigger dynamics node

This example file demonstrates how the built-in trigger types for the Crowd Trigger DOP can be used.

FEMSpheres Example for finiteelementsolver dynamics node

This example demonstrates how to use the FEM Solver to deform spheres when they collide with the ground plane. The spheres have particle based animation on them prior to collision with the ground and are swapped to the FEM solver on collision.

FlipColorMix Example for FLIP Solver dynamics node

This example demonstrates the use of the Flip Solver to mix the colors of a red fluid with a blue fluid to form a purple fluid.

FlipColumn Example for FLIP Solver dynamics node

This example demonstrates how a mixture of fluid colours can have their colour changed by a collision with a static object.

FlipFluidWire Example for FLIP Solver dynamics node

This example demonstrates the use of the Flip Solver and the Fluid Force DOP. The Fluid Force DOP is used to apply a drag force on a wire object according to the motions of a flip fluid. The drag force is only applied at locations where fluid exists in the fluid object.

FluidFeedback Example for Fluid Object dynamics node

This example shows a ball falling into a tank with feedback. This couples the RBD simulation with the Fluid simulation, causing the ball to float rather than sink.

EqualizeFlip Example for Gas Equalize Volume dynamics node

This example demonstrates how the Gas Equalize Volume dop can be used to preserve the volume in a fluid simulation.

EqualizeLiquid Example for Gas Equalize Volume dynamics node

This example demonstrates how the Gas Equalize Volume dop can be used to preserve the volume in a fluid simulation.

grass

This example simulates grass being pushed down by an RBD object. Fur Objects are used to represent the blades of grass and Wire Objects are used to simulate the motion. When a single Fur Object is used to represent the grass, neighbouring blades of grass will have similar motion. Additional objects with different stiffness values can be used to make the motion less uniform. When "Complex Mode" is enabled, two objects are used to represent the grass. The stiffness of each set of curves can be controlled by adjusting the "Angular Spring Constant" and "Linear Spring Constant" parameters on the corresponding Wire Objects.

GuidedWrinkling Example for FEM Hybrid Object dynamics node

This is a setup for guided wrinkling using the hybrid object. The first sim creates a detailed mesh consisting of both tets and triangles that doesn’t have any wrinkles yet. The second sim is targeted to the animation creates by the first sim and this adds in the wrinkles.

MagnetMetaballs Example for Magnet Force dynamics node

This example demonstrates how to use the Magnet Force node on a group of metaballs to force the fragments of an object outwards at the moment of impact.

FluidGlass Example for Particle Fluid Solver dynamics node

This example demonstrates how to get a smooth fluid stream to pour into a glass.

ParticleCollisions Example for POP Collision Detect dynamics node

This example demonstrates the use of the POP Collision Detect node to simulate particles colliding with a rotating torus with animated deformations.

BaconDrop Example for POP Grains dynamics node

This example demonstrates dropping slices of bacon onto a torus. It shows how to extract a 2d object from a texture map and how to repeatedly add the same grain-sheet object to DOPs.

VaryingGrainSize Example for POP Grains dynamics node

This example demonstrates interacting grain simulations of very different sizes.

RagdollExample Example for Cone Twist Constraint dynamics node

This sample creates a simple ragdoll using the cone twist constraint between pieces of the ragdoll.

BlendSolverWithRBDGlue

This example shows how to grab animated key frame data from an RBD Glue object and blend it into a simulation of a cube fragmenting into multiple pieces on impact.

BreakingRock

This is an example of how to use the RBD Glue Object node to create an RBD object that automatically breaks apart on collision. It also demonstrates one technique for breaking a model into pieces appropriate for this sort of simulation.

FrictionBalls Example for RBD Object dynamics node

This example demonstrates the friction parameter on an RBD Object.

RBDInitialState Example for RBD Object dynamics node

This example demonstrates the use of the Initial State parameter of an RBD object.

ActivateObjects Example for RBD Packed Object dynamics node

This example shows how to modify the "active" point attribute of an RBD Packed Object to change objects from static to active.

AnimatedObjects Example for RBD Packed Object dynamics node

This example shows how to use animated packed primitives in an RBD Packed Object and set up a transition to active objects later in the simulation.

DeleteObjects Example for RBD Packed Object dynamics node

This example shows how to remove objects from the simulation that are inside a bounding box.

EmittingObjects Example for RBD Packed Object dynamics node

This example shows how to use a SOP Solver to create new RBD objects and add them to an existing RBD Packed Object.

Chainlinks Example for RBD Pin Constraint dynamics node

In this chain simulation, the individual chain links react to one another in an RBD sim.

RippleGrid Example for Ripple Solver dynamics node

This example demonstrates how to use the Ripple Solver and Ripple Object nodes. Bulge SOPs are used to deform a grid to create initial geometry and rest geometry for the Ripple Object which is then piped into the Ripple Solver.

ScalePieces Example for Script Solver dynamics node

This example demonstrates how to use the Script Solver node to scale fractured pieces of an RBD sim over time.

DelayedSmokeHandoff Example for Smoke Object dynamics node

This example shows a way to turn an RBD into smoke a certain number of frames after the RBD object has hit something.

SourceVorticlesAndCollision Example for Smoke Object dynamics node

This example demonstrates a simple smoke system using a source, keyframed RBD collision objects, and vorticles.

VolumePreservingSolid Example for FEM Solid Object dynamics node

This solid object has a strong volume-preserving force (e.g. flesh). The effect of the volume-preserving force is clearly visible when the object hits the ground plane.

StaticBalls Example for Static Object dynamics node

This example uses static object nodes in an RBD simulation of a grid falling and bouncing off three spheres before it hits the ground.

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.

CrowdPov Example for Agent Cam object node

This example demonstrates how the agent cam can be assigned to a crowd agent to give you the point of view from someone in a crowd simulation.

CaptureDeform Example for Cloth Deform geometry node

This example demonstrates how you can use the Cloth Capture and Cloth Deform nodes to transfer the simulation from a low-res piece of cloth to a hi-res piece of cloth.

LowHigh Example for Dop Import geometry node

This example shows how to create a low res - high res set up to support RBD objects. The two main methods are to reference copy the DOP Import SOP and feed in the high res geometry or to use point instancing with an Instance Object.

dopimportrecordsexample Example for DOP Import Records geometry node

This example demonstrates a creating points for each matching record in the DOP simulation. This lets us create a point for each object or a point for each impact.

ExtractAnimatedTransform Example for Extract Transform geometry node

This example shows how to create packed primitives with animated transforms from deforming geometry that represents rigid motion. The result is ideal for colliders in a rigid body simulation.

CoolLava

This example demonstrates how to cool Lava using the Cool Within Object shelf tool.

FurBallWorkflow Example for Fur geometry node

This example demonstrates how the Fur SOP and Mantra Fur Procedural can be applied to an animated skin geometry. CVEX shaders are used to apply a custom look to the hairs based upon attributes assigned to the geometry.

glueclusterexample Example for Glue Cluster geometry node

This example shows how to use the gluecluster SOP and glue constraint networks to cluster together the pieces of a voronoi fracture. This allows clustering to be used with Bullet without introducing concave objects.

PlateBreak Example for TimeShift geometry node

This example demonstrates how to use the TimeShift SOP to achieve a slow-motion effect during a fracture simulation.

See also

Dynamics nodes