Houdini 18.0 Executing Tasks

PDG node network interface

How to use the unique network editor features of TOP networks.

On this page

See also how to cook the network.

TOP nodes

Work item dots

The distinguishing feature of TOPs nodes is the grid of dots representing the work items in each node. If a node hasn’t generated work items yet, it will not show any dots. You can pre-generate the "static" work items (those items known ahead of time) using Tasks ▸ Generate Static Work Items. Dynamic work items will appear as the network runs (see cooking the network).

To...Do this

Show information about an individual work item

  • Press on a work item dot to show a pop-up info window containing information about the work item, including its attribute values.

  • You can also ⌃ Ctrl + click a dot to open a persistent info window, or right-click the dot and choose Task info.

Hide the dots on one node

  • Click the up-pointing triangle in the bottom-left corner of the node to "collapse" the node, hiding the dots.

  • Click the down-pointing triangle on a collapsed node to show the dots again.

Hide the dots on all nodes

In the menus at the top of the network editor, turn off Tasks ▸ Show Task Graph.

This may be necessary if networks have huge numbers of visible work items. See also the controls in the display options for limiting the number of dots shown on each node.

Limit the number of dots shown on nodes

See the display options.

Show a table of all work item data

Click the table icon in the bottom-right corner of a TOP node to open the task graph table.

The color of the dots normally indicates the individual work item’s status (you can switch to show relative speed as color instead, see visualizing performance).





Bright green

In progress (cooking)

The work item is currently running.

Medium green

Done (cooked)

The work item finished without any warning or error.

Dark blue-grey


The work item has started but is waiting (to be scheduled or for upstream work to finish).


Uncooked/Not cooking

The work item has been generated but hasn’t run yet.



The work item generated a warning.



The work item encountered an error (or the executable returned a non-zero status code).



The user canceled the cook while the task item was running.

Status icon and counts

To the left of each TOP node, Houdini shows an icon indicating the overall status of the work items in the node, and a table of the number of work items with each status. When the node is cooking, a ring around the icon shows the progress of the work items. (If you hide work items with certain statuses using the display options, those items are not included in the progress.)




Not started

This node is not running.


This node has started, but is waiting for its items to be scheduled or for upstream dynamic items to finish.


This node is running, the work items inside are being scheduled on the machine/render farm.


All work items in this node have finished running with no warnings/errors.


At least one work item in this node raised a warning as it ran.


At least one work item in this node raised an error as it ran.

Task graph table

  • To show the task graph table, click the table icon in the bottom-right corner of a TOP node.

    The task graph table shows the metadata of all work items in the graph, or all work items in a particular node.

  • Use the Work items to show menu to choose whether to show all work items in the graph, only the work items in the current node, or only the work items in the node with the output flag.

Tasks menu

This menu appears at the top of the network editor when viewing a TOP network.

Generate Static Work Items

Makes every node in the network generate any "static" work items it knows will be needed ahead of time, based on parameter values and/or incoming static items.

Cook Output Node

Starts cooking the network to produce the final output.

Cook Selected Node

Cooks the network down to the selected node, instead of down to the node with the output flag. This can be useful to test different parts of the network.

Dirty All

Marks all nodes in the network as needing to recook. This means the next time the network cooks, all work items will run.

Delete All Results From Disk

Deletes all result files tracked by work items in the graph.

Dirty Selected Node

Marks the selected node as needing to recook. The next time the network cooks, all work items in the node will run.

Dirty and Cook Selected Node

Forces all work items in the network to recook down to the selected node. This can be useful to test different parts of the network.

Dirty and Cook Output Node

Forces all work items in the network to recook down to the final output.

Delete Selected Node Results From Disk

Deletes all result files tracked by work items in the selected node.

Cancel Current Cook

Stops cooking the network and may cancel "in-flight" processes.

Pause Current Cook

Pauses cooking the network. Any "in-flight" processes will continue to run.

Show Task Graph

Whether to show dots representing work items inside the nodes.

Task Graph Display Options

Opens a window with TOP-specific display options

Show Task Graph Performance

When this is on, the network colors dots according to relative speed or output size, rather than by status. See visualizing performance for more information.


When Show task graph performance is on, this controls whether to color work items by relative cook time or output size.

PDG Service Menu

Opens the PDG Service Menu.

Display options


The "Tasks to show" and "Always show" controls are not very useful and can be very confusing. They may be removed in a future version.

Tasks to show

Important: These controls do not affect static work items.

You can turn off display of (dynamic) work items with certain states.

Always show

These controls override the visibility controls under "Tasks to show".

Sort by

How to order work item dots inside a node body.


If the network is visualizing performance, sort by performance, otherwise sort by index. This is the default.


Sort by the work item state, for example "cooking", "cooked", "failed", and so on.


Sort by each work item’s unique ID.


Sort by the index attribute. This tends to keep child items in line with their parents.



Do not auto-collapse nodes. This is the default and the recommended setting.

By static ancestor

Auto-collapse nodes that don’t have static ancestors of the selected work item.

By batch



Isolate highlighted tasks

When you select a work item, this hides all work items that aren’t ancestors or descendents of the selected item.

Limit rows

Limit the maximum number of rows of dots to show inside nodes. This is a good idea since nodes can (by design or accidentally) easily generate thousands of work items.

Max number of Rows

When Limit rows is on, the maximum number of rows of dots to show inside nodes. When extra rows are hidden, the visible rows will end with a "fade out" effect to show that more work items exist but are not shown.

Tasks per row

How many dots to show on each row inside nodes. The default is 10. Decreasing this number makes the dots bigger, increasing it makes the dots smaller.

Executing Tasks


Beginner Tutorials

Next steps


  • All TOPs nodes

    TOP nodes define a workflow where data is fed into the network, turned into "work items" and manipulated by different nodes. Many nodes represent external processes that can be run on the local machine or a server farm.

  • Processor Node Callbacks

    Processor nodes generate work items that can be executed by a scheduler

  • Partitioner Node Callbacks

    Partitioner nodes group multiple upstream work items into single partitions.

  • Scheduler Node Callbacks

    Scheduler nodes execute work items

  • Custom File Tags and Cache Handlers

    PDG uses file tags to determine the type of an output file.

  • Python API

    The classes and functions in the Python pdg package for working with dependency graphs.