Houdini 19.5 Solaris

Using VEX with USD

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VEX is Houdini’s programming language used for everything from deformers to shaders to solvers. As VEX is a SIMD language, its code/network snippets are designed to run on each ‘element’ being targeted. In LOPs this means primitives by default, meaning there is no need to add a loop to iterate over each target primitive; that happens automatically. Each attribute of the primitives is accessed using the @ syntax, or Bind VOPs.

Wrangle and VOP LOP also have a second mode, Run on Elements of Array Attributes. In this case, the elements over which the code will run are the elements of array properties on primitives. This allows for faster operations over PointInstancer or Points prims, or even the points of heavy meshes.

Build-in variables


Path of the prim, on the stage .


Current element number, whether prim or array element.


Total number of prims or array elements.


The prim type name.


A prim’s kind if set.


The name of a primitive.


The display purpose of the current prim.


The draw mode of the prim.


Returns whether the current prim is active or deactivated.


Returns the visibility of the prim.

USD-specific functions




  • Importing SOP geometry into USD

    Details of how Houdini converts SOP geometry to USD, and how you can control the process.

  • Component Builder

    The Component Builder tool puts down a network snippet for creating a USD model from SOPs, with support for materials, variants, payloads, and layering.


  • Edit node

    Interactively transforms prims in the viewer. Can use physics collisions to position props realistically.

  • Layout node

    Provides tools for populating a scene with instanced USD assets. You can place individual components, paint/scatter components in different ways using customizable brushes, and edit existing instances.

  • Custom Layout Brushes

    How to create layout brush digital assets you can use to customize the behavior of the Layout LOP.


  • Shader Framework

    Describes the Solaris shading framework, including shader node translation to USD primitives.

  • Using MaterialX in Solaris

    Houdini has VOP node equivalents of the MaterialX shader nodes. You can build a shader network using these nodes, or import an existing MaterialX shader, and use them with Karma (Houdini’s USD renderer).

  • UDIM

    You can encode different tiles of a texture space into different texture files, each with its own resolution. You can then specify a texture filename such as kaiju.exr, and Houdini will replace the token with the specific tile address at load time.

Karma rendering