Houdini 12 Network and parameters

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.

Delete animation channels on a parameter

Ctrl-click the parameter, or right-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.

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

Press RMB on the parameter and choose Edit Expression.

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

Press RMB on the parameter and choose Toggle Expression.

View the animation curve generated by an expression

Press RMB on the parameter and choose Scope Channels.

Lock and unlock parameters

If you want to protect a parameter from being edited, press RMB on the parameter in the parameter editor and choose Lock Parameter.

To unlock a parameter again, press RMB on the parameter and choose Unlock Parameter.

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

Text box color coding

Background color Meaning
Light Green

The parameter is controlled by an expression, and the current frame is a keyframe.

Cyan

The parameter is controlled by an expression but the current frame is not a keyframe (or the channel value at the current frame is disabled from the dopesheet).

Yellow

Pending keyframe (the current value at this frame is different from the keyed value, but you have not yet keyframed it).

Orange

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

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.

Copy, paste, and link parameter values

Tip

For parameters with multiple components (for example, a position parameter with X, Y, and Z values) you can click individual component text boxes, or click the parameter label to affect all components at once.

To...Do this
Copy a parameter to the clipboard
Paste a copy of or reference to the copied parameter

  1. Use the table below to decide which type of pasting you want to do.

  2. Press RMB on a parameter in the parameter editor and choose one of the paste items (see below).

    You can paste the value of the copied parameter (if the parameter is controlled by an expression, Houdini will evaluate the value of the expression at the current frame and paste that), the value or expression (if the copied parameter is controlled by an expression, Houdini will paste the expression), or a reference to the copied parameter.

Make one parameter relative to another

  1. Copy the source parameter and paste a reference in the second parameter.

  2. Edit the channel reference expression Houdini inserted in the second parameter.

    For example, to make the second parameter always be the logical opposite of the source parameter, insert a ! (logical not) in front of the ch function. This is especially useful when you have two nodes with Activation parameters (which are 1 for active and 0 for inactive) and you always want one node to be active when the other is inactive and vice versa.

    To make the second parameter go from 0 to 1 as the source parameter goes from 1 to 0, insert 1 - in front of the ch function. This is especially useful when you have two blend factor parameters and you want them to have an inverse relationship, so as one goes up the other goes down and vice versa.

    To make the value of the second parameter always be the value of the source parameter plus 50, edit the expression to ch("path") + 50.

Paste menu item What it does

Paste Copied Values

Pastes in the values of the parameter on the clipboard. If you copied parameters with expressions, this will paste the computed values of the expressions.

Paste Copied Expressions

Pastes the values and expressions of the parameter on the clipboard. Does not convert expressions to values.

Paste Copied References

Pastes a reference to the copied parameter (using the ch expression function). Unlike pasting a copy of the value of the other parameter, this expression will fetch the other parameter’s value every time it is evaluated, so it stays up to date with the current value of the other parameter.

This command inserts an expression with an absolute path to the copied parameter. To insert a relative reference instead, use Paste Copied Relative Refs.

Paste Copied Relative Refs

Same as Paste Copied References, but the ch expression uses a relative path to the copied parameter, instead of an absolute path.

Paste Copied Channels

Pastes a copy of the channel. Once the channel is pasted, it is independent from the original channel and can be modified without altering the original.

Presets and defaults

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.

About auto-scope parameters

“Auto-scoping” is a property of parameters that are commonly animated, to make using the channel list easier. When you select an object, the object’s parameters that are already keyframed and any auto-scope parameters become scoped in the channel list and channel editor.

The commonly animated parameters (such as transforms) on the standard Houdini operator types have auto-scope set.

To make a parameter auto-scope that isn’t already auto-scoping by default, press RMB on the parameter in the parameter editor and choose Set Auto Scope.

When you create a digital asset, you can choose which of the asset’s parameters auto-scope in the Parameters pane of the asset’s type properties window . See how to set up parameters on an asset and how to turn a character into a digital asset.