Houdini 17.0 Nodes Dynamics nodes

Gravity Force dynamics node

Applies a gravity-like force to objects.

On this page

The Gravity Force DOP applies forces on objects as if they were inside a gravity field. The amount of force is proportional to the object’s mass. If an object has twice the mass, it receives twice the force. However, because an object of twice the mass requires twice the force to experience the same net acceleration, the Gravity Force can be thought of as a raw acceleration.

You can add noise to the force applied by this DOP by connecting a Noise DOP to the second input of this node, which adds the noise as subdata of the force data.

Using Gravity Force

  1. Select the dynamic object to apply gravity force.

  2. Click the Gravity Force tool on the Drive Simulation tab.

Note

Gravity force is simply a predefined Force node whose force and direction can be altered in the parameter editor.

Parameters

Force

The amount of force to apply to a unit-massed object. Because the force is scaled by the mass, objects will undergo this acceleration.

If your units are meters, seconds, and kilograms, -9.81 is a good value for Earth’s gravity.

If your units are feet, seconds, and pounds, -32 is a good value for Earth’s gravity.

Sampling Mode

Indicates the preferred sampling level (point, circle, or sphere) to trade accuracy for efficiency of the computation.

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.

CountImpacts Example for Count channel node

This example demonstrates how to count impacts from a DOPs simulation using the Count CHOP. Then, using the values from the Count CHOP, we generate copies of a teapot.

DynamicLights Example for Dynamics channel node

This example demonstrates how to use the Dynamics CHOP to extract impact data from a DOPs simulation, and then modify the data to control lights in the scene.

ExtractTransforms Example for Dynamics channel node

This example demonstrates the use of the Dynamics CHOP to pull transformation information out of a DOP simulation and apply it to Objects.

HoldLight Example for Hold channel node

This example uses the Hold CHOP in conjunction with the Dynamics CHOP to hold a light at the position of an impact from a DOPs simulation until a new impact occurs.

Lookup Example for Lookup channel node

This example demonstrates how to use the Lookup CHOP to play animation based on an event, or trigger.

AnimatedActiveState Example for Active Value dynamics node

This example shows how to use the Active Value DOP to animate the Active state of an object. When an object is not active (it is passive), it is not simulated. To keyframe both the active state of an object and its motion while passive, use the RBD Keyframe Active DOP.

AutoFreezeRBD Example for Active Value dynamics node

This example shows a system for automatically detecting when RBD objects achieve a rest state and then turning off their active status. This will freeze them in place reducing computation time and jitter.

LookAt Example for Anchor: Align Axis dynamics node

This example shows how to build a Look At Constraint which keeps a teapot pointed at a bouncing ball. It shows how to build constraints out of anchors and constraint relationships.

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.

ConstrainedTeapots Example for Apply Relationship dynamics node

This example demonstrates how the Apply Relationship DOP can be used to create multiple constraints with the RBD Pin Constraint node.

MutualConstraints Example for Apply Relationship dynamics node

This example demonstrates how to build mutual constraints between two DOP objects using the Apply Relationship node.

SimpleBlend Example for Blend Solver dynamics node

This example demonstrates how to use the Blend Solver. In this case the Blend Solver is used to blend between an RBD solution and a keyframed solution.

BuoyancyForce Example for Buoyancy Force dynamics node

This example shows how to extract a surface field from another object to use as a buoyancy force source.

AnimatedClothPatch Example for Cloth Object dynamics node

This example shows how a piece of cloth that is pinned on four corners. These corners are constrained to the animated geometry.

BendCloth Example for Cloth Object dynamics node

This cloth example demonstrates how the stiffness of your cloth object can be defined by using the strong or weak bend parameters.

BendDamping Example for Cloth Object dynamics node

This cloth example demonstrates the use of the Damping parameter to control how quickly a cloth object will come to its rest position.

BlanketBall Example for Cloth Object dynamics node

This cloth example shows you how to simulate a ball bouncing on a blanket pinned at all four corners.

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.

ClothUv Example for Cloth Object dynamics node

This is an example that shows how you can specify the warped and weft directions on a triangulated cloth planel using uv coordinates.

Because the uv directions are aligned with the xy directions of the grid, the result looks nearly identical to a quad grid, even though the mesh is triangulated.

The little blue and yellow lines visualize the directions of the cloth fabric. This is enabled in the Visualization tab of both cloth objects.

DragCloth Example for Cloth Object dynamics node

This example shows how adding Normal and Tanget Drag to a cloth object can influence its behaviour.

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.

PanelledClothPrism Example for Cloth Object dynamics node

This example demonstraits a paneling workflow to create a open-ended rectangular prism which keeps its shape.

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.

PointAnchors Example for Constraint Network dynamics node

This example shows how to create a basic constraint network with point anchors.

SoftConstraintNetwork Example for Constraint Network dynamics node

This example shows how to create a simple network of soft constraints, which are used to allow an object to bend before breaking.

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.

AutoFracturing Example for Copy Objects dynamics node

This example shows how to use the Copy Object DOP, in conjunction with a Multi Solver, to automatically break an RBD object in half whenever it impacts another object.

SimpleCopy Example for Copy Objects dynamics node

This example demonstrates the use of the Copy Objects DOP. A single RBD Object is copied 100 times, and assigned a random initial velocity, and a position based on some grid geometry. These 100 spheres are then dropped onto a ground plane.

AnimatedStaticAgents Example for Crowd Solver dynamics node

This example file demonstrates how to set up "animated static" agents for the crowd solver. These agents follow SOP-level animation and can be used for avoidance or turned into ragdolls.

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.

PartialRagdolls Example for Crowd Solver dynamics node

This example demonstrates how to set up a partial ragdoll, where a subset of the agent’s joints are simulated as active objects by the Bullet solver and the remaining joints are animated.

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.

TypesOfDrag Example for Drag Force dynamics node

This sample illustrates three different ways to apply drag on an rbd object: by dragging the linear velocity, by dragging the angular velocity, or by directly changing the angular velocity.

fieldforce Example for Field Force dynamics node

This example demonstrates the use of the Field Force DOP. It shows how to use a particle system to blow around smoke.

CacheToDisk Example for File dynamics node

This example shows how to use the File DOP to cache a simulation to disk and read it back in.

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.

DensityViscosity Example for FLIP Solver dynamics node

This example demonstrates two fluids with different densities and viscosities interacting with a solid object.

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.

SpinningFlipCollision Example for FLIP Solver dynamics node

This scene shows how to create FLIP fluids based on the velocity of geometry by generating new particles from points scattered on the original geometry based on the velocity vectors. It also shows how to set up the original geometry to act as a collision object for the fluid.

VariableViscosity Example for FLIP Solver dynamics node

This example demonstrates interaction between three fluids of varying viscosity and a moving collision object.

FluidWireInteraction Example for Fluid Force dynamics node

This example demonstrates the use of 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 fluid object. The drag force is only applied at locations where fluid exist in the fluid object.

BallInTank Example for Fluid Object dynamics node

This example shows an RBD ball being thrown into a tank of liquid.

FillGlass Example for Fluid Object dynamics node

Fills an RBD container with fluid that enters the simulation by being sourced from another RBD 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.

PaintedGrog Example for Fluid Object dynamics node

This example creates a torus of paint which is dropped on the Grog character. The Grog character is then colored according to the paint that hits him. This also shows how to have additional color information tied to a fluid simulation.

RestartFluid Example for Fluid Object dynamics node

This example shows how to extract part of a fluid simulation and use it to start up a new fluid simulation, possibly with different resolution, location, or size.

RiverBed Example for Fluid Object dynamics node

A simple river bed has a fluid source and fluid sink set up so that liquid rushes down the river.

VariableDrag Example for Fluid Object dynamics node

This example shows how to vary the drag in a fluid simulation. It provides examples of using a specified field to be a high drag zone, of automatically applying drag only to the fluid surface, and of applying negative drag to an area to make the fluid more volatile.

HotBox Example for Gas Calculate dynamics node

This example shows how to take any object with it’s volume representation and add it to the temperature field. You can change the temperature of the object in two ways: by adjusting the volume density value or by adjusting the Gas Calculate microsolver DOP’s source’s Pre-Multiply field.

DiffuseSmoke Example for Gas Diffuse dynamics node

This example demonstrates how to diffuse the density of a smoke simulation using the Gas Diffuse DOP.

CombinedSmoke Example for Gas Embed Fluid dynamics node

In this example, two smoke volumes are merged together using a Gas Embed Fluid DOP and some feathering to help provide a smoother transition between the volumes.

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.

dopexample_gasnetfetchdata Example for Gas Net Fetch Data dynamics node

This example demonstrates the use of Gas Net Fetch Data to have two separate dop simulations exchange data.

UpresRetime Example for Gas Up Res dynamics node

This example demonstrates how the Up Res Solver can now be used to re-time an existing simulation. The benefit of this is that one can simply change the speed without affecting the look of the sim. On the up-res solver there is a tab called Time. The Time tab offers various controls to change the simulation’s speed.

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.

SimpleMultiple Example for Multiple Solver dynamics node

This examples demonstrates how to use a Multiple Solver. In this example, the motion of an object is controlled by an RBD Solver while the geometry is modified by a SOP Solver.

VolumeSource Example for Particle Fluid Emitter dynamics node

This example demonstrates the use of a volume emitter to fill a container with fluid. The volume of the inside of a tank is specified as volume emission geometry, and particles are emitted randomly at points inside of this geometry for a specified number of frames. This example uses an SPH fluid.

Particle fluid buoyancy

This example demonstrates how to couple the Particle Fluid with an RBD object so they both affect each other. The result is a buoyant sphere.

FluidGlass Example for Particle Fluid Solver dynamics node

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

PressureExample Example for Particle Fluid Solver dynamics node

This is a simple example demonstrating pressure-driven flow with no viscosity. This example also demonstrates the use of a constantly emitting source of particle fluid as well as how to surface the fluid using the Particle Fluid Surface SOP.

ViscoelasticExample Example for Particle Fluid Solver dynamics node

This example demonstrates the use of viscous and elastic forces in a particle-based fluid to generate viscoelastic fluid behaviour. The result is a fluid-like object that tends to resist deformation and retain its shape.

ViscousFlow Example for Particle Fluid Solver dynamics node

This example demonstrates highly viscous fluid flow using particle-based fluids. Fluids of this form could be used to simulate slowly-flowing fluids such as lava or mud.

WorkflowExample Example for Particle Fluid Solver dynamics node

This somewhat complicated example is meant to demonstrate a simple workflow for simulating, storing, surfacing and rendering a particle fluid simulation. Three geometry nodes in the example are named Step 1, Step 2 and Step 3 according to the order in which they are to be used. They write out particle geometry to disk, read the geometry in and surface it, and read the surfaced geometry from disk, respectively. The example also has shaders and a camera built in so that it can be easily rendered.

The fluid animated in this scene models a highly-elastic gelatin-like blob of fluid.

AdvectByVolume Example for POP Advect by Volumes dynamics node

This example demonstrates how to use POP Advect by Volumes to advect particles using the velocity from a smoke simulation.

ParticlesAttract Example for POP Attract dynamics node

This example demonstrates how to use the POP Attract node to get a group of particles to follow the motion of an animated sphere. POP Interact and POP Drag nodes are also used in the example to control the interaction between particles and their distance from the sphere.

PointAttraction Example for POP Attract dynamics node

This example demonstrates how to use the POP Attract node with it’s type set to Point in order to control particle attraction on a per point basis.

SphereAxisForce Example for POP Axis Force dynamics node

This example shows three different ways in which the POP Axis Force node can be used with it’s type set to sphere to control your particle simulation.

TorusAxisForce Example for POP Axis Force dynamics node

This example demonstrates how to use the POP Axis Force node to cause a group of particles to billow upwards.

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.

ColorVex Example for POP Color dynamics node

This example shows three different ways to use VEXpressions in your POP Color node to color your particles.

CurveForce Example for POP Curve Force dynamics node

This example demonstrates the use of the POP Curve Force node to control the flow of a particle sim AND a flip fluid sim.

CurlForce Example for POP Force dynamics node

This example demonstrates how to use the POP Force node to add curl noise to your particle simulation.

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.

KeyframedGrains Example for POP Grains dynamics node

This example demonstrates keyframing the internal grains of a solid pighead to create an animated puppet.

VaryingGrainSize Example for POP Grains dynamics node

This example demonstrates interacting grain simulations of very different sizes.

SwarmBall Example for POP Interact dynamics node

This example demonstrates the use of the POP Interact node to control the distance between particles and create a ball shaped swarm.

LookatTarget Example for POP Lookat dynamics node

This interactive example demonstrates the use of the POP Lookat node. Hit play and move the green target handle around in the viewport. The cone particles will orient themselves towards the target as you move it around.

DragCenter Example for POP Property dynamics node

This example shows how you can use the Drag Center parameter of the POP Property node to apply an off-center drag to falling objects.

ProximateParticles Example for POP Proximity dynamics node

This example demonstrates how to use POP Proximity node to find nearby particles and set attributes based on their proximity to one another.

CrossTheStreams Example for POP Stream dynamics node

This example shows how the POP Stream node can be used to define streams with different behaviours within your particle simulation.

BillowyTurbine Example for Pyro Solver dynamics node

This example uses the Pyro Solver and a Smoke Object which emits billowy smoke up through a turbine (an RBD Object). The blades of the turbine are created procedurally using Copy, Circle, and Align SOPs.

DampedHinge Example for RBD Angular Spring Constraint dynamics node

This example shows how to use the RBD Angular Spring Constraint to create a damped hinge.

Stack Example for RBD Auto Freeze dynamics node

Teapots are dropped every ten frames onto a ground plane. The RBD AutoFreeze DOP is used to detect and freeze the teapots that have come to rest, stabilizing and speeding up the simulation.

RagdollExample Example for Cone Twist Constraint dynamics node

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

ShatterDebris Example for RBD Fractured Object dynamics node

This example demonstrates the how the shatter, RBD Fractured Object, and Debris shelf tools can be used to create debris emanating from fractured pieces of geometry.

First, the Shatter tool (from the Model tool shelf) is used on the glass to define the fractures. Then the RBD Fracture tool is used on the glass to create RBD objects out of the fractured pieces. Then the Debris tool is used on the RBD fractured objects to create debris.

StackedBricks Example for RBD Fractured Object dynamics node

This example shows how to create a large number of RBD objects from a single SOP. It also shows how a velocity point attribute can be used to set the initial motion for the objects.

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.

ChoreographedBreakup

This example shows how one can control the break up of any glued object through the use of the RBD State node.

A torus, composed of spheres, is glued together. An additional sweep plane is defined. Any sphere which ends up on the wrong side of the sweep plane is broken off the torus and left to bounce on its own. This lets the break up of the torus to be controlled over many frames.

ChoreographedTubeBreakup

This example shows how one can control the break up of any glued object through the use of the RBD State node.

In this version of the choreographed breakup example, a moving plane is used to choreograph the breakup of a fractured tube. As the plane passes each piece, it is allowed to break off from the rest of the tube.

ShatterGlass

This example uses an RBD projectile to shatter a piece of glass. The glass is made up of simple trangular shards glued together.

This example also demonstrates a situation where using volume based collision detection would not work, and so the objects are treated as infinitely thin surfaces when performing collision detection.

Pendulum Example for RBD Hinge Constraint dynamics node

This example shows how to use the RBD Hinge Constraint to create a hinge joint between an RBD Object and a world space position or other RBD object.

SimpleKeyActive Example for RBD Keyframe Active dynamics node

This example uses the RBD Keyframe Active node to switch from a keyframed animation to an RBD Solver, and back to keyframed animation. This same animation could be created using a Switch Solver or Blend Solver, but this approach is simpler if the only requirement is switching from keyframed to simulated motion for a few RBD Objects.

DeformingRBD Example for RBD Object dynamics node

This example demonstrates a rigid body dynamics simulation involving deforming geometry. A wobbling torus is dropped onto a ground plane.

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.

SimpleRBD Example for RBD Object dynamics node

This example demonstrates a simple rigid body dynamics simulation using the RBD Object DOP. A single sphere is dropped onto a ground plane.

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.

SpeedLimit Example for RBD Packed Object dynamics node

This example shows how to limit the speed of specific objects in the simulation.

Chain Example for RBD Pin Constraint dynamics node

This sample creates a chain of RBD objects connected to each other using constraints.

Chainlinks Example for RBD Pin Constraint dynamics node

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

Pendulum Example for RBD Pin Constraint dynamics node

This example shows how to use the RBD Pin Constraint to pin RBD Objects to world space positions or other RBD objects.

GravitySlideExample Example for Slider Constraint dynamics node

This sample creates a box which can only slide and rotate on one axis, using the Slider Constraint.

PaddleWheel Example for RBD Solver dynamics node

This example combines a number of elements and features of RBD to create a simulation of a paddle wheel being hit by a large number of falling objects.

This example demonstrates features such as resolving penetrations, gluing simple objects together to create more complex objects, grouping of objects, and constraints.

Weights Example for RBD Spring Constraint dynamics node

This example shows how to use the RBD Spring Constraint to create springs that will break once a threshold force or length is exceeded.

InheritVelocity Example for RBD State dynamics node

This example demonstrates the use of the RBD State node to inherit velocity from movement and collision with other objects in a glued RBD fracture simulation.

Simple Example for RBD Visualization dynamics node

This example demonstrates a simple rigid body dynamics simulation using the RBD Object DOP. A single sphere is dropped onto a ground plane. It adds in an RBD Visualization DOP to show the impact forces that are applied as a result of the collision.

ReferenceFrameForce Example for Reference Frame Force dynamics node

An RBD vase filled with water performs the water simulation in the vase’s reference frame.

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.

Freeze Example for Script Solver dynamics node

This example uses the Script Solver to remove objects from the simulation once they fall below a certain threshold velocity. This technique can be used to speed up simulations that are known to settle down to a static arrangement.

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.

SumImpacts Example for Script Solver dynamics node

This example uses the Script Solver and SOP Solver to change the color of RBD objects based on the total impact energy applied to the object at each timestep.

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.

RBDtoSmokeHandoff Example for Smoke Object dynamics node

This example shows a way to turn an RBD object into smoke. It uses multiple different colored smoke fields inside the same smoke object.

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.

DentingWithPops Example for SOP Solver dynamics node

This example combines a number of important DOPs concepts.

  • First, it uses both POP Solver and RBD Solver objects interacting with each other in a bidiretional manner. The RBD object affects the particles, and the particles affect the RBD object.

  • Second, the RBD object atually uses a multi-solver to combine an RBD Solver with a SOP Solver. The RBD Solver controls the motion of the overall object, while the SOP Solver performs the denting of the geometry.

  • Third, the SOP Solver extracts impact information from the RBD Solver to perform the denting. It extracts this information using DOP expression functions.

The end result is a simulation of a torus that is bombarded by a stream of particles. The particles bounce off the torus, and also cause the torus to move. In addition, each particle collision causes a slight denting of the torus.

VisualizeImpacts Example for SOP Solver dynamics node

An example that shows how you can visualize impact data in an RBD simulation by using a SOP Solver to add custom guide geometry to the RBD Objects.

This example has three toruses falling on a grid with green lines showing the position and magnitude of impacts. The force visualization is added as ancillary geometry data to the actual toruses, so the RBD Solver is entirely unaware of the effect. The SOP Solver could also be used as an independent SOP network to extract impact visualization from an RBD Object.

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.

SimpleVortex Example for Vortex Force dynamics node

This example uses a few balls to visualize the force generated by a Vortex Force DOP.

AnimatedSkin Example for Wire Glue Constraint dynamics node

This example shows how the Wire Glue Constraint DOP can constrain a wire object to animated geometry.

CompressedSpring Example for Wire Object dynamics node

This example demonstrates how an initial pose may be specified for a wire object.

BeadCurtain Example for Wire Solver dynamics node

This example uses the Wire Solver to simulate a bead curtain. A stream of RBD balls are thrown at the curtain, and through feedback the curtain and balls are mutually affected by the collisions.

BendingTree Example for Wire Solver dynamics node

This example shows how to use the Wire Solver to simulate a flexible tree built with the LSystem SOP.

BreakWire Example for Wire Solver dynamics node

This example demonstrates how to break wire constraints on a per point basis. The wire solver is set up to constrain certain points if it finds an attribute named 'pintoanimation'.

Pendulum Example for Wire Solver dynamics node

This example shows how to mutually affect an object at the constraint point and the object at the bob of the pendulum.

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.

PackedFragments Example for Assemble geometry node

This example shows how you can break a sphere into packed objects for use in a rigid body simulation using the Assemble SOP.

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.

ConnectedBalls Example for Connectivity geometry node

This example demonstrates how to use an attribute generated by the Connectivity SOP to color different pieces of geometry from a DOPs simulation.

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.

ProxyGeometry Example for Dop Import geometry node

This example demonstrates a technique of using the DOP Import SOP to allow the use of proxy geometry in a DOP simulation. One set of geometries are used in the simulation, then the transform information for those objects is applied to higher resolution versions of the geometry.

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.

ColourAdvect

This example demonstrates how you can use the Fluid Source SOP to source and advect colours from an additional volume into a smoke 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.

PartitionBall Example for Partition geometry node

This example demonstrates how to break geometry in a DOPs simulation using the Partition SOP to determine the DOP 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.

TransformFracturedPieces Example for Transform Pieces geometry node

This example demonstrates using the Transform Pieces SOP to transform high-resolution geometry from the results a DOPs rigid-body fracture simulation that used low-resolution geometry.

RampParameter Example for Parameter VOP node

This example shows how to control the particle colours using the temperature attributes from a pyro simulation using a Ramp Parameter VOP node.

Dynamics nodes