Houdini 19.5 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

MMB on the input to show the shader effects menu.

Apply an effect in the parameter editor

Click the menu to the right of the parameter.


  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 Reflection intensity parameter, then choose Noise ▸ Cellular noise.

Houdini automatically:

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 on the input and choose Hide input nodes.

To show the nodes again, MMB on the input and choose Expose input nodes.

Inputs that are hidden appear as lines fading out. Hidden inputs that are Parameter nodes appear as pegs. You can click both to select the hidden node 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.

The node state button in the top-right corner of each VOP node lets you switch the node between three display modes: Show all visible inputs, Hide all inputs, and Show only connected inputs. Note that inputs with collapsed input nodes (e.g. promoted parameters) do not appear in “show only connected inputs” mode.

Independent of the node state button, you can mark certain inputs as always hidden. The Surface model VOP uses this to show only the most commonly used. To show or hide an input, MMB the input in the network editor, and choose either Collapse input connector or Show input connector.

The menu button for the parameter corresponding to a hidden input displays a hidden icon.


Using materials

Textures and UVs

Creating materials

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Other renderers