You can right-click shaders, Arnold VOP networks and ROPs to upgrade them to the current version of Arnold and HtoA. You can also globally convert all the deprecated shaders in the scene from the Arnold menu. Conversion scripts for the deprecated standard and hair shaders, the Arnold ROP from a previous version of HtoA and the discontinued alSurface and alHair shaders are provided. For shaders, the conversion will attempt to match the look as closely as possible with standard_surface or standard_hair shader.

Shaders are created within Arnold Shader Network nodes. These nodes are also used for Light Filters and Environment Effects.

In the SHOP context Tab > Arnold > Arnold Shader Network to create an arnold_vopnet1 node. Double-clicking or pressing "I" enters a custom VEX builder context where Arnold shaders and nodes can be networked together.

You can create shaders in /mat in the arnold_materialbuilder vop network as well as the old way in /shop in the arnold_vopnet vop network. Use the material flag to enable picking of the vopnet as a material at the object level.

The OUT_Material node allows collecting the surface/displacement/volume Arnold shader graphs into one material. You can then connect the output to a collect node for example in the /mat context.

Arnold shaders created in /mat

Output Nodes

There are three types of output depending on the purpose of the shader network; Material, Light, and Environment. The result of the shader network must be connected to the input of the relevant output node. Multiple Outputs of different types can be contained within the same shader network. If multiple outputs of the same type exist, Arnold will use the first one translated by HtoA.

Material Output
Light Output
  • color: For attaching a shader (like a physical_sky) to be used as the color of a light. 
  • light_filter #Light Filter nodes are connected here. As each is connected another input will appear.

Environment Output

Shader Assignment

To assign a vopnet drag it from the SHOP onto the geometry or use the Operator Chooser in the geometry Material tab.

The 'jump to operator' in the material tab will go to the Arnold shader network, rather than jumping to the shader inside. This is Houdini's behavior because you're assigning a SHOP and thus it brings you to it, not inside.

Export Arnold Materials

You can export materials in an arnold_vopnet or from an OUT_material VOP by right-clicking with the context-sensitive menu. This exports all of the shader graphs connected (surface, displacement, and volume).

Shader List

These are the available shaders and nodes.

Core Shaders

AOV Shaders

  • AOV Read Float
  • AOV Read Int
  • AOV Read RGB
  • AOV Write Float
  • AOV Write Int
  • AOV Write RGB

User Data

  • User Data Float
  • User Data Int
  • User Data RGB
  • User Data RGBA
  • User Data String

Shading State

  • State Float
  • State Int
  • State Matrix
  • State RGB
  • State Vector

Ramp Shaders

  • Ramp RGB
  • Ramp Float

Math Shaders

  • Abs

  • Add
  • Atan
  • Cache
  • Complement
  • Cross
  • Divide
  • Dot
  • Exp
  • Fraction
  • Invert
  • Is Finite
  • Ln
  • Log
  • Max
  • Min
  • Mix
  • Modulo
  • Multiply
  • Negate
  • Normalize
  • Pow
  • Reciprocal
  • Sign
  • Sqrt
  • Subtract
  • Trigo

Utility Shaders

  • Cache
  • Clamp
  • Color Correct
  • Compare
  • Fetch
  • Length
  • Linearize
  • Passthrough
  • Random
  • Range
  • Space Transform
  • Switch

Data Types

  • Color Convert

  • Int To Float
  • Float To Int
  • Float To Matrix
  • Float To RGB
  • Float To RGBA
  • RGB To Float
  • RGB To Vector
  • RGBA To Float
  • Matrix To Float
  • Vector To RGB



Light Filters

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