Houdini 20.0 Networks and parameters

Parameter editor

How to change the behavior of nodes by changing their parameters.

On this page

Overview

Parameters are the options on an individual node. For example, each light has a Translate parameter that controls the light’s position, a Color parameter that controls the color of the light cast, and numerous other parameters.

Editing

To...Do this

Edit a parameter value

  • Click in a parameter value box and type a new value.

  • Press Alt + E to edit the field contents in an external editor (as defined by the $EDITOR environment variable).

Undo to the previous value of a field

Click RMB in the text field.

Reset a value to the default

⌃ Ctrl + MMB click the parameter.

Find a particular parameter on a node

Click the search icon in the top right of the parameter editor to show the search toolbar.

Delete animation channels on a parameter

⌃ Ctrl + LMB click the parameter, or RMB click it and choose Delete channels.

Change a value by dragging in the viewer

  1. Select one or more scoped channels in the channel list .

  2. In the viewer pane, hold J and drag LMB to modify the parameter value(s), or drag MMB to show a value ladder.

Change a value using the value ladder

  1. Press MMB on a parameter name or an individual edit field. The value ladder appears.

  2. Drag up and down the ladder to choose the magnitude of the change. Drag left and right to change the value.

Create a new parameter editor pane that always edits at a certain node

  1. Select the node you want to edit.

  2. Click the “new tab” button in the pane header and choose New pane tab type ▸ Parameters.

  3. In the new parameter editor pane, click the Pin button to pin the parameter editor to the node so it won’t follow the selection.

Create a relationship between two parameter values

See referencing parameter values.

Protect a parameter from being changed

  • Right-click the parameter in the parameter editor and choose Lock Parameter.

  • To unlock a parameter again, right-click the parameter and choose Unlock Parameter.

Locked parameters have a gray background in the edit field(s).

Entering expressions

To...Do this

Enter a short expression directly

Type the formula directly into the parameter’s text box.

Enter an expression using an editor window

Right-click the parameter and choose Expression ▸ Edit Expression.

Switch between viewing the computed value for the current frame and the expression itself

Right-click the parameter and choose Expression ▸ Toggle Expression.

View the animation curve generated by an expression

Right-click the parameter and choose Channels ▸ Add to Channel List.

Text box color coding

Houdini color codes the parameter text boxes according to the current channel and keyframe status.

Background color

Parameter background

State

Black

No channel

This parameter is not animated. It has no channels associated with it.

Green

Keyed

This parameter is animated (controlled by an expression) and you are on a keyframe.

Yellow

Pending changes

This keyed parameter has been changed, but hasn’t been explicitly keyed. You need to explicitly key a changed parameter if auto-commit is turned off.

You can set Houdini to automatically commit changes on keyframes.

Blue

'Tween

This parameter is animated (either with keyframes or an expression), but you are not on a keyframe.

(Click the name of a parameter to switch between showing the current value and the expression.)

Orange

Overridden by CHOPs

This parameter is currently controlled by a channel operator (CHOP).

Light blue

Muted channel

This parameter is animated (either with keyframes or an expression), but the channel is muted in the dopesheet.

Light yellow

Empty channel

This parameter has an empty channel (a channel that doesn’t hold any keyframes). If you delete all the keyframes on the graph, you end up with a parameter with an empty channel.

You can delete the channel on the parameter (RMB click the parameter and choose Delete Channels) to change the parameter to a black background, or add a single key to turn the parameter into a single keyframe channel (green background).

Purple

Non-default expression language

This parameter uses a different expression language from the current default. Note that this does not indicate which expression language the parameter is set to, only that it is not the current default. Since the default is usually HScript, this often indicates that the parameter has a Python expression.

See python parameter expressions for more information.

Parameter underline

The parameter editor also gives a visual hint of whether a parameter is selected in the channel list by displaying a colored underline for the selected parameters. Turn the parameter underline on or off in the Houdini animation preferences Edit ▸ Preferences ▸ Animation, option Underline in the Parameter Editor. If you turn on Use Channel Color in the animation preferences, the underline will have the same color as the channel in the graph view.

Selected channel list parameters are underlined in the parameter editor

If you turn off Use Channel Color, an orange underline will be displayed for all the selected channels in the channel list.

Use Channel Color option turned off

Parameters that reference other nodes

In Houdini, various parameters contain references to other nodes instead of numeric or string values.

To...Do this

Insert the name of a node in a node parameter

  • Type the path to the node in the parameter’s text field. You can use a relative path from “this” node (the node with the parameter you're editing).

  • Click the node chooser icon next to the parameter to choose a node from a tree list of all existing nodes.

  • Drag a node from the network editor and drop it onto the parameter’s text field to insert its name in the field.

Edit the parameters of a referenced node

  • Click the jump icon next to the parameter’s text field to jump to the referenced node’s parameters in the current editor.

  • Ctrl-click the jump icon to edit the referenced node’s parameters in a new window. This lets you quickly edit the referenced node’s parameters without losing focus on the current node.

See pasting references.

Presets

A Preset file contains preset values for the parameters of an operator. You can use them to fill in common values, or to save important variations of a node. Saved presets are node specific.

Use the menu items in the gear pop-up menu on the toolbar to load, save, and select presets.

To...Do this

Save the parameter values of a node to a preset

  1. In the parameter editor, click the gear menu and choose Save Preset.

  2. Give the preset an name, for example center_pivot and click Save Preset.

For more information see the save preset dialog help.

Set the parameter values of a node from a preset

In the parameter editor, click the gear menu and choose the name of a preset.

Delete a node preset

In the parameter editor, click the gear menu and choose Delete preset.

Use the delete preset dialog to choose the preset you want to remove.

Note

Load from .preset File and Save to .preset File are older ways of saving and applying presets. Using the above methods to save and apply presets is the preferred method. However, .preset files are ASCII files, which are easier to edit than the .idx files that the new method uses, so they still have some usefulness.

Defaults

  • The parameter editor shows values different from the default as bold.

  • You can temporarily change the original “factory” defaults for a type of node. For example, you can change the default Depth for the Subdivide node to 2, so new Subdivide nodes will start with Depth at 2, and reverting to defaults will reset the value to 2, not the original “factory” default of 1.

    This does not affect the “bold” display style in the parameter editor. The parameter editor always bolds values that are different from the original defaults, regardless of how you've changed the defaults.

    Changes to the defaults only last for the current “session”. If you quit and restart Houdini, it will start with the original defaults.

  • If you want to permanently change the default values for newly created instances of a node, you can use a creation script (HOUDINIPATH/scripts/category/nodename.py or nodename.cmd) to modify new nodes of a type as they are created.

To...Do this

Reset a single parameter to the default value

In the parameter editor, right-click the parameter label and choose Revert to default.

or

⌃ Ctrl + MMB click the parameter label.

Reset all parameters on a node to their default values

In the parameter editor, click the gear menu and choose Revert to Factory Defaults.

Make a node’s current values the new default

In the parameter editor, click the gear menu and choose Override Factory Defaults for This Session.

Revert the defaults for a node to their original values

In the parameter editor, click the gear menu and choose Revert to and Restore Factory Defaults.

This will also revert all the parameters on the node to their original default values.

Toolbar

Node menu

Shows the icon of the node you are currently editing. Click to show the node’s context menu (this is the same menu you get if you right-click the node in the network editor).

Node type

For example, a Geometry object will show Geometry.

Name text box

The node’s name. When you create a node it has a default name of the operator type name plus a number. You can edit the text box to change the node’s name (this is the same as clicking the node’s name in the network editor).

Node names can only contain letters and numbers. Spaces are not allowed in the name.

Gear menu

Use the items in this menu to edit various node and parameter settings. See gear menu for more information.

  • Edit the node’s parameter interface. See the Edit Parameter Interface window.

  • Save presets and reload presets.

  • Edit the node’s delete script (this lets you define a script that Houdini will run if/when the node is deleted).

Info

Click to show a small window of information about the node. For example, a geometry node will show the bounding box, number of points, attributes, and other information. This is the same information represented in the node info window in the network editor.

Expression language

This menu controls which expression language you will use to write new expressions (HScript expressions or Python). You can choose the expression language of each individual parameter using the parameter’s context menu.

Search

Click to show or hide a toolbar with controls for searching and filtering the parameters.

Help

Click to view documentation for the current node.

Often you want to quickly jump to one specific parameter in a complex interface, or show only the parameters that are not at their default values, or find parameters with expressions. The filter and search toolbar makes this easy.

To...Do this

Show the filter and search toolbar

In the top-right corner of the parameter editor, click the search icon in the parameter editor’s toolbar to show or hide the search and filter controls.

  • The pop-up menu on the left filters which parameters are shown in the parameter editor:

    • All parameters (in this mode, the text box only searches parameters, not tabs or other groups).

    • All parameters and headings (in this mode, the text box searches parameters as well as tab names and group headings).

    • Only parameters that are time-dependent (that change based on the current frame number). For example, parameters with expressions that use $F.

    • Only parameters that are shown in the animation editor (see Channel List for more information).

    • Only parameters that have the auto-add to channel list flag turned on.

    • Only parameters that are selected in the scene graph.

    • Only parameters that are not at their default values. This makes it easy to see what parameters have been edited.

    • Parameters with expressions.

    • Parameters with overrides. Usually this means the parameter’s value is computed by a CHOP network. For example, motion effects set up a CHOP network to control parameters.

    • Only parameters that are marked as invisible or are hidden because of hide when conditionals (see conditional rules)

  • The pop-up menu on the left also defines the search criteria that is used on parameters:

    • Parameter Names or Labels.

    • Parameter Names.

    • Parameter Labels.

    • Parameter Raw Value (in this mode, the current expression string is searched. If there is no expression, the parameter value is searched instead. If you have animation, the expression can change we time changes).

    • Parameter Evaluated Value (in this mode, all parameters are evaluated and the evaluated value string is searched.)

  • The pop-up menu on the left has extra options to customize the search:

    • Exact Match ( use exact pattern matching instead of simply finding the pattern within the string )

  • The text box on the right filters parameters by the current search criteria.

    When the filter is set to “Raw value or expression”, the search box searches the parameter value rather than name/label.

Tip

The menu button text gives a summary of the current search mode and criteria. If “Exact Match” is turned on, the label will start with “Match” instead of “Search”.

Tip

Houdini preserves the tab structures around the matching parameters, so you still might need to click through tabs to find the parameter you're looking for.

Gear menu

Edit Parameter Interface

Opens a window allowing you to add, edit, or remove spare parameters on the current node instance.

This is different from right-clicking the node and choosing Type Properties. That edits the parameter interface of all nodes of that type, while this edits the extra parameters that might exist on this particular node.

Edit Rendering Parameters

Opens a window allowing you to add, edit, or remove render properties on the current node instance.

The only difference between this and Edit Parameter Interface is this automatically shows the tab of available render properties instead of the tab of available spare parameter types.

Edit Deletion Script

Opens a window allowing you to edit a script that will run when/if the current node is deleted.

(You can set the deletion script programmatically using hou.Node.setDeleteScript.)

Edit Comments

Opens a window allowing you to edit the comment string associated with the current node.

This is the same as editing the comment in the node info window in the network editor.

Revert Parameter Interface

Reverts the parameter interface of the current to the standard initial interface for its node type.

Delete All Spare Parameters

Deletes any spare parameters on the current node.

Add Spare Input

Adds a spare reference to another node. These are used in compiled node blocks to avoid external references in expressions.

Add Visualizer

The items on this submenu let you attach a visualizer to the this node.

Show Visualizers

Opens a window that lets you edit the settings of any visualizers attached to the current node.

Save Preset

Saves the current parameter values as a preset you can recall or copy onto other nodes of the same type.

Save as Permanent Defaults

Saves the current parameter values as the defaults for new nodes of the same type.

Delete Preset

Opens a window allowing you to delete a saved preset for the current node type.

Revert to Factory Defaults

Resets all parameter values to the defaults for this node.

Revert to and Restore Factory Defaults

Resets all parameter values and their defaults to the “factory” default shipped with Houdini, reverting any changes and/or custom defaults.

Override Factory Defaults for This Session

Saves the current parameter values as the defaults for new nodes of the same type, but only until you restart Houdini.

Type Properties

Opens the Type Properties window for the current node type. For assets this lets you edit the type’s parameter interface and other options.

The rest of the menu lists any saved presets for this node type.

Parameter context menu

You can edit the contents of this menu in PARMmenu.xml.

Revert to Previous Value

Returns to the previous parameter value.

Channels

This submenu controls items for working with animation channels.

Add to Channel List

Adds this parameter to the list of parameters shown in the animation editor (see Channel List for more information).

Isolate in Channel List

Replaces any parameters shown in the animation editor with this parameter (see Channel List for more information).

Remove from Channel List

Removes the parameters from the animation editor (see Channel List for more information).

Auto-Add

Toggles the auto-add option for this parameter. An “auto-add” parameter is automatically added to the channel list when you select the object.

Select in Channel List

Selects this parameter in the list of parameters shown in the animation editor (see Channel List for more information).

Select/Replace in Channel List

Selects this parameter and clears the previous selection in the list of parameters shown the animation editor with this parameter (see Channel List for more information).

Deselect in Channel List

Deselects this parameter in the list of parameters shown in the animation editor (see Channel List for more information).

Auto-Select

Toggles the auto-select option for this parameter. An “auto-select” parameter is selected in the Channel List when you select the object.

Pin in Channel List

Pins this parameter in the list of parameters shown in the animation editor (see Channel List for more information).

Pin/Replace in Channel List

Pins this parameter and clears the previous pins in the list of parameters shown the animation editor with this parameter (see Channel List for more information).

Unpin in Channel List

Unpin this parameter in the list of parameters shown in the animation editor (see Channel List for more information).

Unmute Channel

Turns on the channel so that it affects the animation.

Mute Channel

Turns off the channel so that it does not affect the animation.

Create Channel Group

Create a channel group from the selected channels. RMB click on a parameter tab or from a selection in the channel list to bring up this option

Select Nodes from Channels

Select the nodes in the viewport from the selected channels. This is really useful on character rigs where all of the handles are promoted on the top level digital asset. You can hold S and LMB on a parameter label or tab to select controllers. This can also be done from the channel list, but you need to press S alone without clicking.

Select/Append Nodes from Channels

Same as Select Nodes from Channels, but appending to the current viewport selection. You can hold Shift+S and LMB on a parameter label or tab to append controllers to the selection.

Extrapolation

Set the channel extrapolation of all the selected channels. You can choose from the following extrapolation modes: Default, Hold, Cycle, Extend, Slope, Cycle Offset, and Oscillate. The extrapolation can be applied before and/or after the channels end. See Edit Channel Properties for descriptions of the different extrapolation modes.

Edit Channel Properties

Opens an Edit Channel Properties window allowing you to edit channel metadata such as how to extend before and after the keyframed animation.

Keyframes

This submenu controls items for working with keyframes.

Set Keyframe

Sets a keyframe on the parameter at the current frame.

Remove Keyframe

Removes any keyframe on the parameter at the current frame.

Step to Previous Key

Go to the previous keyframe for this parameter.

Step to Next Key

Go to the next keyframe for this parameter.

Bake Keyframes

Writes the computed animated values of this parameter directly into the parameter at each frame and then removes the keyframe animation.

Expression

This submenu contains items related to expressions.

Toggle Expression

Switch the text box between showing the computed value for the current frame, and the expression itself. This is the same as clicking the parameter label.

Edit Expression

Open the parameter value in an editor window. This is useful for long, multi-line expressions.

Expand String Value

Turns string expansion on or off in the parameter value.

Use Python

Interpret expressions in this parameter as Python expressions.

Use HScript expressions

Interpret expressions in this parameter as HScript expressions.

Motion Effects

This submenu contains canned effects you can apply to transform parameters. The effects are implemented using CHOP networks you can then modify and elaborate if needed.

Jump to Effect Network

Jumps to the CHOP network implementing any effect(s) on the parameter.

Edit Parameters

Choose an applied effect from this menu to edit the effect’s parameters.

Enable Effect

Toggles any motion effect(s) on the parameter on or off.

The rest of the menu lists the available effects. Available effects include Cycle, Cycle with Offset, Despike, Lag, Limit, Noise, Shift, Smooth, Spring, Stretch, and Wave.

You can edit this part of the menu using EffectsMotionMenu.xml.

Reference

The items in this menu let you create references in this parameter to other data in the scene.

Scene Data

Creates a reference in this parameter to a transform or parameter value elsewhere in the scene.

Local Variable

Creates a reference in this parameter to one of the node’s local variables. This is useful if you don’t already know or forget what local variables are available.

Local Attribute

Creates a reference in this parameter to one of the attributes in the node’s geometry.

Copy Parameter

Copies a reference to this parameter to the clipboard. You can then choose to paste the data into another parameter in different ways.

Paste Values

Pastes the value(s) from the copied original. If you copied parameters with expressions, this will paste the computed values of the expressions instead of the expressions.

Paste Expressions/Channels

Pastes animation (keyframes and expressions) from the copied original.

Paste Relative References

Pastes references (using the ch expression function using relative paths) to the copied original. This links the two parameters, so changes to the first parameter are pulled into the second parameter.

See linking parameters with references for more information.

Paste Other

This submenu contains lesser-used paste methods.

Paste Expressions

Pastes the expression(s) (if any) from the copied original at the current time.

Paste Absolute References

Like Paste Relative References, but pastes ch expressions using absolute paths instead of relative paths.

Delete Channels

Removes any keyframe animation from this parameter.

Include in Take

Adds this parameter to the current take, allowing you to modify it in the take.

Lock Parameter

Prevents this parameter from being edited or animated. For example, Houdini will not allow you to type in the parameter’s text box or use a handle associated with the parameter.

Unlock Parameter

Unlocks this parameter if it was locked. This allows you to edit the parameter.

Revert to Defaults

Resets this parameter to the default value. You can change the default with Make Current Value Default.

Revert to and Restore Factory Defaults

Resets this parameter and its default to the “factory” default shipped with Houdini, reverting any changes and/or custom default.

Make Current Value Default

Makes this parameter’s current value the default. New instances of the node type will use this value, and the Revert to defaults menu item will revert to this value.

Export Parameter to Type Properties

Adds parameter to the Existing Parameter list in the Operator Type Properties dialog.

More

This submenu contains lesser-used items for modifying the parameter.

View Dependencies

Opens a window listing dependencies (references on other nodes to this parameter) and references (references in this parameter to other nodes).

Bypass Spare Parameter

Disables this parameter, so the node acts like the parameter doesn’t exist (if it is a spare parameter).

Delete Spare Parameter

Deletes the parameter from the node interface (if it is a spare parameter).

Bind to Viewport Ladder Handle

Sets this parameter as the parameter controlled by the MMB ladder interactions in the viewport.

Unbind All Viewport Handles

Removes any custom handles bound to this parameter.

See also

Networks and parameters

Networks

  • Network editor

    How to create, move, copy, and edit nodes.

  • Network navigation

    How to move around the networks and move between networks.

  • Connecting (wiring) nodes

    How to connect nodes to each other to make them work together.

  • Network types and node flags

    Flags represent some state information on the node, such as which node represents the output of the network. Different network types have different flags.

  • Badges

    Badges indicate some status information about a node. They usually appear as a row of icons below the name of the node.

  • Find nodes in a network

    How to use the Find dialog to find nodes based on various criteria.

Editing parameters

Next steps

Expressions

Guru level

Reference