naming_conventions.md

Arnold USD Naming Conventions

In order to expose the entirety of the Arnold features in USD, we supply custom schemas for Arnold primitives in USD, and we support Arnold-specific attributes on regular USD prims. This documents the naming conventions in use to map Arnold node and parameters names in USD.

Arnold attributes on USD prims

Additional Arnold attributes on native USD prims (geometry, lights, etc.) need to be set as primvars in the arnold namespace:

def DomeLight "my_light"
{
 float intensity=2
 int primvars:arnold:max_bounces=99
}

Primvars will be converted as user data on the Arnold nodes, at the exception of those in the arnold: scope that will be translated as built-in attributes. In the above example "int primvars:arnold:max_bounces = 99" will be equivalent to "int arnold:max_bounces=99"

Arnold Shaders

Arnold shaders are supported as UsdShade Shader prims. The info:id attribute should be the Arnold shader name, prefixed by the arnold namespace. The shader parameter are placed in the inputs scope.

def Shader "my_shader"
{
    uniform token info:id = "arnold:standard_surface"
    color3f inputs:base_color = (0,0,1)
}

For more details about UsdShadeShader schemas, see https://graphics.pixar.com/usd/docs/api/usd_shade_page_front.html

Arnold Nodes

Any Arnold node can be represented in USD, with a camel-cased node type, prefixed with "Arnold":

def ArnoldStandardSurface "my_shader" {}
def ArnoldSetOperator "my_operator" {}
def ArnoldPolymesh "my_mesh" {}
def ArnoldSkydomeLight "my_light" {}

For these nodes, the attribute names are the Arnold parameter names and are not namespaced.