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 and 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`, not a type name. 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.