SdrShaderProperty represents an input or output on SdrShaderNode. It has the following core fields.

Field	Description
name	Name of the property
type	Sdr type of the property
isOutput	When true, the property is an output. When false, the property is an input

All other fields are optional and thus spiritually belong more to metadata than to core fields.

Connectability of properties to other properties is a core feature described by methods SdrShaderProperty::CanConnectTo and SdrShaderProperty::IsConnectable.

Typing in Sdr

SdrShaderProperty deals with two typing systems.

At construction, SdrShaderProperty resolves given information to a logical Sdr type. Its corresponding Sdf type is automatically calculated upon invocation of SdrShaderProperty::GetTypeAsSdfType. Metadata-based controls may modify the resulting Sdr and Sdf types; these are discussed in the following sections.

Metadata

SdrShaderPropertyMetadata contains named metadata for SdrShaderProperty and has support for custom user-defined metadata.

Below is a table of the most frequently used named metadata for easy reference. Descriptions below mirror the documentation on SdrShaderPropertyMetadata itself. These named metadata items are tokenized here. In code to reference, for example, the "label" metadata key, use SdrNodeMetadata->Label.

Key	Location	Description
label	metadata	UI hint for a user-friendly string representation
help	metadata	Help message for this property
widget	metadata	UI hint describing an appropriate widget, e.g. "number", "slider"
page	metadata	Page group this property appears on, if any. Nested pages should be delimited by ":"
shownIf	metadata	Expression evaluating to true when this property should be shown. See SdrShaderProperty::GetShownIf
hints	field	Other UI hints associated with this property
options	field	Specifies the finite pre-determined values this property is meant to have
defaultValue	field	Sdr-typed default value for this property
connectable	metadata	Whether this property can connect to other properties. True by default.
validConnectionTypes	metadata	List of valid connection types; doesn't affect SdrShaderProperty::CanConnectTo
arraySize	field	Array size
tupleSize	metadata	Tuple size. This is independent of array size and describes an array's "column count"
isDynamicArray	metadata	Indicates whether this property's array type is dynamically sized
isAssetIdentifier	metadata	When true, the computed Sdf type is SdfValueTypeNames->Asset or AssetArray
renderType	metadata	Provides more info for Sdr types without analogous Sdf types (see Special Types)
role	metadata	When "none", a base Sdr type replaces the ingested Sdr type ("float3" replaces "color3")
sdrUsdDefinitionType	metadata	SdfValueTypeName that overrides any computed Sdf type for this property
defaultInput	metadata	Whether the value held by this property is the default input for the node
colorspace	metadata	Colorspace for this property

In general, metadata can be authored either by shader writers or parser plugin writers. Choice of when to author these items depends on the desired workflow.

Sdr Type Resolution

SdrShaderProperty's logical type is described by the constructor arguments type (Sdr type) and arraySize, and the metadata item isDynamicArray.

During construction, if the metadata role set to "none", the type and arraySize fields are transformed to base types according to this map . For example, "float3" replaces "color3".

Sdf Type Conversion

An Sdf type is represented by SdfValueTypeName. When triggered by a call to SdrShaderProperty::GetTypeAsSdfType, the conversion process from the Sdr typing system to SdfValueTypeName takes into account multiple data items comprising the logical Sdr type described above in Sdr Type Resolution.

Normally, SdfValueTypeName conversion is performed according to these maps. However, the following metadata items alter this conversion process.

isAssetIdentifier should be injected if the property is logically an asset. This metadata item guides the type mapping to choose SdfValueTypeNames->Asset over SdfValueTypeNames->String when the base Sdr type is string.
sdrUsdDefinitionType explicitly specifies an SdfValueTypeName. This direct specification replaces the regular conversion process. This metadata value must be an explicit TfType value alias (see SdfValueTypeName::GetAliasesAsTokens) associated with the SdfValueTypeName – this generally matches .usda type declarations. Examples follow.
- "bool" represents SdfValueTypeNames->Bool
- "bool[]" represents SdfValueTypeNames->BoolArray
Note that Sdr doesn't have a "bool" Sdr type, so a logically "bool"-typed property must have an Sdr type of int and use an sdrUsdDefinitionType of "bool".

Special Types

Three types are specific to Sdr and have no corresponding SdfValueTypeName.

struct - Struct types
terminal - Certain properties represent 'terminal' ports (ie. surface, displacement, volume, etc)
vstruct - An abstract struct type that can connect to any other 'vstruct', and connections are only made if a matching vstruct member is found.

These special types have no reasonable corresponding SdfValueTypeName, so we map them to SdfValueTypeName->Token, which is typically reserved for an Unknown type.

For these cases, traditional methods of accessing type information will give incomplete info. For example: SdrShaderProperty::GetType returns a "struct" token without indicating what kind of struct it represents, and SdrShaderProperty::GetTypeAsSdfType().GetSdfType returns SdfValueTypeNames->Token, which is even more ambiguous than "struct".

Therefore to provide more complete type info, the renderType metadata should be authored when creating a SdrShaderProperty with one of the above special types.

On a Struct, the metadata should be renderType = struct structName, where structName is the actual struct's typename
On a Terminal, the metadata should be renderType = terminal terminalName where terminalName is the actual kind of terminal
On a Vstruct, the metadata should be renderType = vstruct, since there is no further specific type name for a vstruct

A user can find the original struct type or terminal type of one of these properties by examining the 'renderType' metadata on the property directly.

Type Behavior Examples

shader TestOSLShader
(
    color foo = color(1.0, 1.0 1.0),
    token bar = "baz",
    token surface = ""
    [[
        string renderType = "terminal surface"
    ]]
)

In the above example, the properties would be translated as follows:

Property	SdrPropertyType	SdfValueTypeName
foo	SdrPropertyTypes->Color	SdfValueTypeNames->Color
bar	SdrPropertyTypes->String	SdfValueTypeNames->String
surface	SdrPropertyTypes->Terminal	SdfValueTypeNames->Token