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This node fetches a piece of data from a simulation object so that it can be modified or attached to some other object.
The output data can be given a different name from the input data. You can reattach the renamed data to the original source object using an Apply Data DOP, thereby making a copy of an existing piece of data.
The number of objects on the input is irrelevant to the evaluation of this node. Only one of the input objects will be used as the source for the data.
Data is only extracted from the source object if the activation parameter is non-zero.
The activation parameter supports object specific local variables, but note that the variables are evaluated for the object to which the output data is being attached. The variables are not evaluated for the source object.
The object from which to fetch the data.
You can use group names, object names, object ids, and/or
wildcard characters to match an object, and the negation
^) to eliminate objects from consideration. If
multiple objects match, Houdini uses the one with the lowest
object ID as the source object.
Source Data Name
Data matching the Source Data Name will be extracted from the source object and provided as the output to this node.
Houdini renames the fetched data to the Data Name. A new name lets you re-apply the data to the original object, thereby copying subdata.
If this field is blank, the Source Data name is used.
One, and only one, of the objects connected to this input is the source from which the data is fetched. Use the Source object parameter to choose which object to fetch data from.
The data fetched from the input object.
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.
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).
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.
This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.
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
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).
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).
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).
This string contains a space separated list of the unique object identifiers for every object being processed by the current node.
This string contains a space separated list of the names of every object being processed by the current node.
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 == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).
This value is the simulation frame (see variable SF) at which the current object was created.
This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).
This is a string value containing the name of the object being processed.
Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.
The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named "myobject",
strcmp($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).
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.
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.
The following examples include this node.
This example shows how to extract a surface field from another object to use as a buoyancy force source.
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.
Extracts the velocity field from a smoke simulation to use as a wind force on a POP simulation.
This example demonstrates how to use another active RBD Object as the source for the Field Force DOP. Two balls bounce inside a cube, one of the balls is set to repel the other according to force values stored on its geometry.
This example demonstrates two fluids with different densities and viscosities interacting with a solid object.
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.