Parameter editor

Parameters are the “options” of a node. Changing the parameters changes the look or behavior of the node. For example, a Sphere SOP has position and radius parameters.

Editing parameters

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 (set using the `$EDITOR` environment variable).
Undo to the previous value of a field	Click in the text field.
Reset a value to the default	Ctrl + 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	Select one or more scoped channels in the channel list . In the viewer pane, hold J and drag to modify the parameter value(s), or drag to show a value ladder.
Change a value using the value ladder	Press on a parameter name or an individual edit field. The value ladder appears. Drag up and down the ladder to choose the magnitude of the change. Drag left and right to change the value.

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 on the parameter and choose Edit Expression.
Switch between viewing the computed value for the current frame and the expression itself	Press on the parameter and choose Toggle Expression.
View the animation curve generated by an expression	Press 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 pink background in the edit field(s).

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.

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 press on the node’s tile in the network editor
Name	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 textbox to change the node’s name (this is the same as clicking the name next to the node’s tile 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 Load and save parameter presets. Edit the node’s parameter interface. See the Edit Parameter Interface window. Save presets. Once you save a preset Edit the node’s delete script (this lets you define a script that Houdini will run if/when the node is deleted). Edit the node’s comment string.
Help (question mark)	Click to view documentation of the node’s parameters.

Edit field color coding

different from the keyed value, but you have not yet keyframed it).

operator (CHOP).

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
Orange	The parameter is currently controlled by a channel

Controls

Angle icon	For edit fields which accept angular measurements, type the number of degrees in the edit field or press and drag on the angle icon to set the angle graphically.
Sliders
Polar jack	For edit fields which accept angular measurements, type the number of degrees in the edit field or drag the small point at the intersection of the two rings in the polar jack.
Input list	Some operators, such as the Merge SOP and Switch SOP, allow multiple inputs to their single input connector. In these operators, an input list appears in the parameters, where you can reorder or disconnect any of the inputs.
Color controls	See editing color parameters .

Parameter pop-up menu

Toggle Expression	Switch the text box between showing the computed value for the current frame and the expression itself.
HUD Sliders	See HUD sliders .
Step to Prev/Next Key, Set/Remove Keyframe	See how to manage parameter keyframes .
Copy Parameter, Paste Copied ..	See how to copying and pasting parameter values .
Scope Append Channels, Scope Channels	Show the parameter(s) in the channel editor.
Delete Channels	Removes any animation on the parameter, making it a static, constant value.

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	Press on a parameter in the parameter editor and choose Copy Parameter.
Paste a copy of or reference to the copied parameter	Use the table below to decide which type of pasting you want to do. Press 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	Copy the source parameter and paste a reference in the second parameter. 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:

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.

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

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.