Houdini 20.0 Nodes TOP nodes

TOP Fetch TOP node

Cooks another TOP network.

On this page
Since 17.5

This node can be used to cook a different TOP network. The other network can exist in the same .hip file or an external file, and will be cooked via the active scheduler. The other TOP network is evaluated in a separate process from the current one.

This node works in two steps. First work items are generated to cook the external TOP network referred to by the TOP Path parameter. The attributes and input files associated with each work in this node are made accessible to the fetched network using the standard work item JSON format. The path to the JSON file is exported as $PDG_FETCH_JSON_FILE in the environment used to cook the fetched network. The fetched network can use a TOP Fetch Input node to load that work item into its own network.

When the remote TOP network is cooked, the work items on the output node of that network are saved to disk and reported back to PDG. Then these items are re-created in the TOP Fetch node. The items visible on the TOP Fetch node are those re-created items.


The $HH/help/files/pdg_examples/top_topfetch example shows how you can use this node to fetch a TOP network.


TOP Fetch

Generate When

Determines when this node will generate work items. You should generally leave this set to “Automatic” unless you know the node requires a specific generation mode, or that the work items need to be generated dynamically.

All Upstream Items are Generated

This node will generate work items once all of the input nodes have generated their work items.

All Upstream Items are Cooked

This node will generate work items once all of the input nodes have cooked their work items.

Each Upstream Item is Cooked

This node will generate work items each time a work item in an input node is cooked.


The generation mode is selected based on the generation mode of the input nodes. If any of the input nodes are generating work items when their inputs cook, this node will be set to Each Upstream Item is Cooked. Otherwise, it will be set to All Upstream Items are Generated.

TOP Path

The path to the TOP network within the .hip file specified in the Hip File Path parameter.

Hip File Path

The path to the .hip file that contains the TOP network to fetch.

Custom Output Dir

When on, this parameter determines where the output .json files are written to for the work items that were fetched from TOP Path. When off, the .json files are written to the working directory of the scheduler used to cook the fetched node.

Cook Sequentially

When on, work items in this node will cook one at a time in the order they appear in the node. Once one of the TOP fetch work items fails, the remaining work items will also be marked as failed as well. Otherwise, if the toggle is disabled, work items in this node will cook in parallel.

Load Work Items from Fetched Network

When on, this parameter recreates the output work items from the fetched network in this node. In order to do this, the node is set to dynamic because it relies on cooked outputs produced during the fetch operation. When off, the node creates exactly one work item for each fetch operation, and the node is set to static because it no longer depends on cooked outputs. Output work items are stored in a .json file on those work item(s).

Keep Failed Work Items

When on, outputs from failed work items in the fetched network are imported and recreated by the TOP Fetch node. Otherwise, failed work items are ignored. This parameter can only be used when Load Work Items from Fetched Network is enabled.

Preserve Work Item Indices

When on, work items loaded from the fetched network will keep their original index values. Otherwise, the index of the fetched work items will be set to the index of the parent work item for the fetch task. This parameter can only be used when Load Work Items from Fetched Network is enabled.


TOP Scheduler Override

This parameter overrides the TOP scheduler for this node.

Schedule When

When enabled, this parameter can be used to specify an expression that determines which work items from the node should be scheduled. If the expression returns zero for a given work item, that work item will immediately be marked as cooked instead of being queued with a scheduler. If the expression returns a non-zero value, the work item is scheduled normally.

Work Item Label

Determines how the node should label its work items. This parameter allows you to assign non-unique label strings to your work items which are then used to identify the work items in the attribute panel, task bar, and scheduler job names.

Use Default Label

The work items in this node will use the default label from the TOP network, or have no label if the default is unset.

Inherit From Upstream Item

The work items inherit their labels from their parent work items.

Custom Expression

The work item label is set to the Label Expression custom expression which is evaluated for each item.

Node Defines Label

The work item label is defined in the node’s internal logic.

Label Expression

When on, this parameter specifies a custom label for work items created by this node. The parameter can be an expression that includes references to work item attributes or built-in properties. For example, $OS: @pdg_frame will set the label of each work item based on its frame value.

Work Item Priority

This parameter determines how the current scheduler prioritizes the work items in this node.

Inherit From Upstream Item

The work items inherit their priority from their parent items. If a work item has no parent, its priority is set to 0.

Custom Expression

The work item priority is set to the value of Priority Expression.

Node Defines Priority

The work item priority is set based on the node’s own internal priority calculations.

This option is only available on the Python Processor TOP, ROP Fetch TOP, and ROP Output TOP nodes. These nodes define their own prioritization schemes that are implemented in their node logic.

Priority Expression

This parameter specifies an expression for work item priority. The expression is evaluated for each work item in the node.

This parameter is only available when Work Item Priority is set to Custom Expression.


FetchingATopNetwork Example for TOP Fetch TOP node

This example demonstrates how to use Top Fetch node to execute a TOP network out of process and return the results.

See also

TOP nodes