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 now create shaders the new Houdini way 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.
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.
- color: For attaching a shader (like a Physical Sky 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.
- atmosphere: For connecting the atmosphere nodes fog and volumetric scattering and atmosphere_volume.
- background: For connecting background shaders like Sky or Physical Sky sky or physical_sky.
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.
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).