Glossary

Term	Definition
Shader	A UsdShade Shader prim representing a processing node. In SPG, a shader is either a custom node (wrapping a CUDA kernel or Slang shader and its Lua launch script through info:spg:sourceAsset) or a built-in node (identified through info:id). Inputs can be resource-inputs connected to AOVs (opaque) or value-inputs carrying typed values (int, float, bool).
Lua Launch Script	The .lua file named after the GPU source and sitting beside it, GrayscaleKernel.cu.lua for a CUDA node and GrayscaleKernel.slang.lua for a Slang one. Called per frame to validate inputs, describe the outputs, and return a launch configuration.
subIdentifier	The info:spg:sourceAsset:subIdentifier attribute on a Shader. Names the entry point in the GPU source, an extern "C" function on CUDA or a [shader(...)] entry point on Slang, and the Lua function to invoke. Optional: without it the Shader prim’s own name is used for both.
shape	A resource’s dimensions, as a Lua table with one entry per dimension. Height-first for images: shape[1] is height, shape[2] is width. Refer to Shapes and Types.
rank	How many dimensions a resource has, which is how many entries its shape holds.
dtype	What one element of a resource is: the kind of number, its width in bits, and how many of them make an element. A dtype is a value taken from the cuda or slang table, such as cuda.uchar4 or slang.float. It can be compared against another dtype and called to wrap a value for the GPU. Refer to Shapes and Types.
Prim table	What a launch script gets for a prim of the scene: rtx.stage.prim(path), an entry of rtx.product.cameras or rtx.product.render_vars, or rtx.product itself. It answers path, local_matrix, world_matrix and any attribute by name, reads them when asked, and cannot be assigned to. Refer to The rtx Lua Table.
On the stage	Published for the renderer at the time a launch script runs. Loading a scene puts its prims on the stage with what the renderer needs of them; custom attributes arrive only when the load names their prim. Refer to What Is on the Stage.
AOV	Arbitrary Output Variable: a named output of a RenderProduct, such as LdrColor. A node reads AOVs and can publish its own. Refer to Publish, Overwrite and Read Back AOVs.
RenderVar	The prim that names an AOV through sourceName. Its omni:rtx:aov exposes the AOV to a node, and its omni:rtx:aov.connect publishes a node output under that name. Refer to What You Can Author in USD.
Resource-input, resource-output	A port declared opaque inputs:X or opaque outputs:Y. It carries an AOV, a buffer another node produced, or a sensor composite; the launch script sees its descriptor. Refer to Ports.
Value-input	An inputs: attribute that is not opaque, such as float inputs:strength. The launch script gets a wrapper whose .value is the raw Lua value. Refer to Value-Input Types.
Composite	What a lidar or radar publishes under one RenderVar: several named channels and params in place of one image. inputs["X"].isComposite tells the two apart. Refer to Read a Sensor Composite.
Memory	Storage only the node reads and writes, kept across frames for as long as the node lives. Stated on self.memory in the launch script. Refer to Keep State Across Frames.
Stateful output	An output SPG hands back as the same resource next frame, marked with a trailing cuda.stateful or slang.stateful, or with self.stateful = true. It stays a port that can be published and connected. Refer to Keep State Across Frames.