Houdini 20.0 Materials

Working with VOPs

Tips for working with shaders in the VOP network.

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Reading geometry attributes in a shader

You can use the Bind VOP to get the value of a geometry attribute at the current point, or to set an attribute. The Parameter VOP will also pick up the value of attributes with the same name as the parameter. This lets you create parameters such as “Color” (Cd) that can be specified using an overall parameter or overridden using an attribute.

Shader effects

Shader effects are like presets you can apply to VOP node inputs. They add useful nodes to the input, for example “promote” the input to be a parameter on the parent node, or making the input gets its value from a texture, or add noise to current input.

You can choose effects in either the parameter editor or the network editor. The result is the same.

To...Do this

Apply an effect in the network editor

MMB on a node’s input to show the shader effects menu.

Apply an effect in the parameter editor

Click the menu to the right of the parameter. This icon changes when the parameter is connected to a filter. You can see the different states in Example directly below.


  1. In a Material Shader Builder network, create a Principled Shader node.

  2. In the parameter editor, click the menu to the right of the Reflectivity parameter, then choose Noise ▸ Cellular noise.

Houdini automatically:

  • Creates a Cellular Noise node and wires it into the reflect input.

  • Promotes useful inputs from the noise node up to the parent material.

The menu icon next to VOP parameters in the parameter editor changes depending on the corresponding input:

Not connected

Connected to a parameter (promoted)



Hiding and showing inputs

Collapsing branches of the network can help keep the network tidy.

To...Do this

Collapse down all the nodes going into an input

MMB directly on the input and choose Hide Input Node(s) from the drop-down menu.

To show the nodes again, MMB on the input and choose Expose Input Node(s).

Hidden inputs appear as short lines terminated by a blank input. Hidden inputs that are Parameter VOPs appear as pegs. You can double-click both to show all hidden nodes connected to the input.

Hide the actual input rows on the node

Nodes sometimes have a large number of inputs (for example the Surface model VOP has an input for almost every parameter). There are several techniques for hiding unused inputs.

In the lower right corner of each VOP node you can see a trio of stacked lines. The icons let you switch between three display modes:

  1. Show all visible inputs.

  2. Show only connected inputs. Note that inputs with collapsed input nodes (e.g. promoted parameters) do not appear in “show only connected inputs” mode.

  3. Hide all inputs.

Independent of the node state button, you can mark certain inputs as always hidden. To hide or show an input, LMB the input in the network editor, and choose either Hide Input Connector or Show Input Connector. Invisible inputs are represented through a hidden icon.


Using materials

Textures and UVs

Creating materials

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