Switch
dynamics node
Passes one of the input object or data streams to the output.
See also: Merge, Split Object, Switch Solver
The Switch DOP accepts any number of object or data streams as input, and sends just one of them through to its output. All inputs connected to this node must be of the same type, either objects or data, not a mix of the two.
When objects are connected to the inputs, the objects on the other streams are removed from the simulation. This can be used to easily switch from simulating one set of objects to another part way through the simulation. It can also be used to select from a variety of object creation mechanisms.
When data streams are connected to the inputs, the switch parameter is evaluated for each object that wants data from this node. This node can be used to assign one of a set of data to each object based on some information about each object, or even randomly.
Parameters
|
Select Input |
The zero based index of the input number which should be passed through to the output. When switching objects streams, this parameter is evaluated only once, and so cannot include any object specific local variables. When switching data streams, this parameter is evaluated for each object attaching this data and so object specific local variables can be used. |
Inputs
|
All |
The objects or data coming into the input specified by the Select Input parameter are passed through to the single output. |
Outputs
|
First |
The objects or data coming into the input specified by the Select Input parameter are passed through to the single output. |
Local variables
|
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 |
|
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 |
|
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 |
|
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 |
|
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. |
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:
$positionx + 0.1
…to make the object move 0.1 units along the X axis at each timestep.