Arbitrary Attributes

Katana provides the ability to export arbitrary attributes to renderers. This information takes on a renderer-specific form at render time, such as user data for Arnold and primvars for RenderMan.

In its simplest form, an arbitrary attribute can be defined through its scope and value, as shown in the following OpScript code snippet:

Interface.SetAttr("geometry.arbitrary.myFloat.scope", StringAttribute("primitive"))
Interface.SetAttr("geometry.arbitrary.myFloat.value", FloatAttribute(1.0))

In the following example, a single float is converted to a color3 data type:

Interface.SetAttr("geometry.arbitrary.myFloatToColor3.scope", StringAttribute("primitive"))
Interface.SetAttr("geometry.arbitrary.myFloatToColor3.value", FloatAttribute(0.1))
Interface.SetAttr("geometry.arbitrary.myFloatToColor3.outputType", StringAttribute("color3"))

In this example, two colors are defined and then converted to uniform color[2] when rendering with RenderMan:

Interface.SetAttr("geometry.arbitrary.myColorArray.scope", StringAttribute("primitive"))
Interface.SetAttr("geometry.arbitrary.myColorArray.value", FloatAttribute({0.1, 0.2, 0.3, 0.4, 0.5, 0.6}))
Interface.SetAttr("geometry.arbitrary.myColorArray.inputType", StringAttribute("color3"))
Interface.SetAttr("geometry.arbitrary.myColorArray.elementSize", IntAttribute(3))

A simple example with each face of a cube assigned an alternating texture using an indexed array:

Interface.SetAttr("geometry.arbitrary.myIndexedArray.scope", StringAttribute("face"))
Interface.SetAttr("geometry.arbitrary.myIndexedArray.indexedValue", StringAttribute({"textureA.tx", "textureB.tx"}))
Interface.SetAttr("geometry.arbitrary.myIndexedArray.index", IntAttribute({0, 1, 0, 1, 0, 1}))

Type	Attribute	Description
string	geometry.arbitrary.<group>.scope	The scope of the attribute. Valid values are: primitive Constant. face Uniform. point Varying and vertex. For curves, this matches vertex. vertex Face varying. For curves, this matches Face varying and varying. Support for the different scope types depends on the renderer’s capabilities. Therefore, not all of these are supported in every renderer.
string	geometry.arbitrary.<group>.inputType	Types of values in value or indexedValue. It’s important to note that the specified inputType must match the footprint of the data as described. Valid values are: float double int string color3 color4 normal2 normal3 vector2 vector3 vector4 point2 point3 point4 matrix9 matrix16 Support for different input types depends on the renderer’s capabilities. Therefore, not all of these are supported in every renderer.
string	geometry.arbitrary.<group>.outputType	Output type for the arbitrary attribute can be specified, if the intended output type (and footprint) differs from the input type but can be reasonably converted. Examples of reasonable conversions include: float -> color3, color3 -> color4.
any	geometry.arbitrary.<group>.value	Attribute containing the value. The type is dependent on the type specified. The type of the value can be int, float, double, or string. The value can also be specified as an indexed list using the index and indexedValue attributes (see below).
int	geometry.arbitrary.<group>.index	List of indices. If no index is present, the index is implicitly defined by the scope.
any	geometry.arbitrary.<group>.indexedValue	List of values. The types of values in the list can be int, float, double, or string.
int	geometry.arbitrary.<group>.elementSize	This optional attribute determines the array length of each scoped element. This is used by some renderers, for example, RenderMan maps this to the [n] portion of a RenderMan type declaration: uniform color[2].
int	geometry.arbitrary.<group>.isArray	This optional attribute informs the renderer plug-in that the arbitrary attribute should be declared as an array (when set to 1) or a scalar (when set to 0). When this attribute is not set, the renderer plug-in typically infers this information from the length of the arbitrary attribute value.