SdrRegistry

SdrRegistry is a singleton that provides methods to find shader information. Shader information populates into the registry via two stages that are customizable via plugins.

1. Discovery finds shader definition locations and produces SdrShaderNodeDiscoveryResults.
2. Parsing reads shader definitions and produces SdrShaderNodes.

Discovery runs at registry initialization time, and parsing runs on demand.

The entire flow looks something like this:

• Alice wants to introduce a new shadingSystem "elm" that doesn't have existing plugins, so she writes new discovery and parser plugins. She chooses discoveryType "tree" to associate the new plugins with each other.
• During initialization, the registry finds all discovery and parser plugins. Then, it runs all discovery plugins and stores the discovery results.
• Alice requests a shader node with identifier "foo" and shadingSystem "elm" from the registry.
• A SdrShaderNodeDiscoveryResult with identifier "foo" and shadingSystem "elm" exists in the registry. This result has discoveryType "tree". The registry finds the parser plugin associated with discoveryType "tree" and runs it to parse a shader node from the discovery result.
• A parsed SdrShaderNode is returned to Alice, after which she can load its source into her runtime for execution.

Note that each node is parsed only once. If the node is requested again, the cached parsed node is returned.

Discovery

At registry initialization, the registry discovers shaders by running discovery plugins.

A filesystem-based discovery plugin _SdrFilesystemDiscoveryPlugin is active by default. This plugin is configurable via environment variables indicating paths and file extensions to search. However, we recommend that renderers or shading systems adopting Sdr provide their own discovery plugins to avoid coupling configurations for multiple parser plugins.

Users may implement custom discovery plugins to find filesystem-based nodes (a typical case), search a database, a cloud service, or any other system that might contain shaders. If shaders are scattered across multiple systems, a discovery plugin can be created for each.

To build your own discovery plugin, please take a look at the following references:

• Documentation of base class SdrDiscoveryPlugin
• Best practices for SdrShaderNode identifier, name, and function (see Style Guidelines)
• Example UsdMtlx discovery plugin implementation

Parsing

Once the registry knows about shader nodes via discovery plugins, parser plugins parse nodes upon request and provide the registry with the resulting information. This includes input and output property information, node metadata, and other information that usually can only be gleaned by reading source implementation files.

To build your own parser plugin, please take a look at the following references:

• Documentation of base class SdrParserPlugin
• Best practices for SdrShaderNode fields and metadata (see Metadata)
• Example UsdMtlx parser plugin implementation

Query API

The registry ships with a query API whose components are SdrShaderNodeQuery and SdrShaderNodeQueryResult. Additional convenience query functions are provided by shaderNodeQueryUtils.h.