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Output dynamics node

Serves as the end-point of the simulation network. Has controls for writing out sim files.

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The Output DOP is usually used to mark the end of a DOP simulation chain. It should normally always have the Output flag set on itself.

It also provides the capabilities of the Dynamics ROP.

Output from this node can be played back using DOP Network Playback

Parameters

Save to Disk

Saves the simulation to disk as a sequence of .sim files.

Save to Disk in Background

Starts another copy of Houdini in the background and instructs that copy to save out the simulation as a sequence of .sim files. This allows one to continue working and load the .sim files as they complete.

Start/End/Inc

Specifies the range of frames to render (start frame, end frame, and increment). All values may be floating point values. The range is inclusive.

These parameters determine the values of the local variables for the output driver.

$NRENDER

The number of frames to be rendered by the output driver.

$N

The current frame being rendered (starting at 1 and going to $NRENDER).

Render with Take

Uses the settings in a particular take while rendering. Choose Current to use the current take when rendering.

Output File

The file to save the simulation state to. Make sure to include $SF in the filename to write out separate files for each frame.

Output Every Sim Frame Using $SF

Every single simulation frame will be output, rather than just the frames hit by the step rate of the frame range. In this mode one just has to set the entire range without worrying about how sub-stepping will be set up.

$SF should be used instead of $F in the file name in these cases.

Initialize Simulation OPs

Force all simulation OPs to be reset. This includes DOP Networks, POP SOPs, and other OPs that cache their results.

This is the safest way to render out a simulation, because it starts the simulation from scratch and discards any partial simulations you might have done with different parameters. However, throwing away an already-cooked simulation can be expensive, especially for relatively slow solvers such as fluids.

Alfred Style Progress

A percentage complete value is printed out as files are written. This is in the style expected by Pixar’s Alfred render queue.

Inputs

All

All the objects connected to the input of this node are fed out through the single output.

Outputs

First

All the objects or data connected to the input of this node are fed out through the single output.

Locals

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.

ClipLayerTrigger Example for Agent Clip Layer dynamics node

BreakingSprings Example for Constraint Network dynamics node

ControlledGlueBreaking Example for Constraint Network dynamics node

Hinges Example for Constraint Network dynamics node

CrowdHeightField Example for Crowd Solver dynamics node

FollowTerrain Example for Crowd Solver dynamics node

FootLocking Example for Crowd Solver dynamics node

PartialRagdolls Example for Crowd Solver dynamics node

PinnedRagdolls Example for Crowd Solver dynamics node

Stadium Crowd Example Example for Crowd Solver dynamics node

Street Crowd Example Example for Crowd Solver dynamics node

ClipTransitionGraph Example for Crowd Transition dynamics node

GuidedWrinkling Example for Hybrid Object dynamics node

BaconDrop Example for POP Grains dynamics node

KeyframedGrains Example for POP Grains dynamics node

TargetSand Example for POP Grains dynamics node

VaryingGrainSize Example for POP Grains dynamics node

FrictionBalls Example for RBD Object dynamics node

RBDInitialState Example for RBD Object dynamics node

AnimatedObjects Example for RBD Packed Object dynamics node

DeleteObjects Example for RBD Packed Object dynamics node

SpeedLimit Example for RBD Packed Object dynamics node

StaticBalls Example for Static Object dynamics node

CrowdPov Example for Agent Cam object node

AgentRelationshipBasic Example for Agent Relationship geometry node

MountainSplash Example for Attribute Transfer geometry node

CoolLava Example for Fluid Source geometry node

TransformFracturedPieces Example for Transform Pieces geometry node

Fuzzy Logic Obstacle Avoidance Example Example for Fuzzy Defuzz VOP node

See also

Dynamics nodes