Python: SPG Generating Node

An SPG node with no input AOV at all. Every value it needs is a typed USD attribute, and it draws a checkerboard into its own output, which the scene publishes as Checker.

The run checks itself: it rebuilds the same checkerboard on the host from the attributes the scene authored and compares the two pixel for pixel.

Running

uv run main.py

The first step compiles the kernel with NVRTC and can take up to a minute on a cold shader cache. A successful run writes _output/checker.png and prints pixels differing from the host-computed pattern: 0. A difference above zero exits non-zero.

The Node

-- Launch script for a node with no resource-input.
--
-- Nothing hands this node a resource, so there is no descriptor to take a shape
-- from. The size comes from typed USD attributes instead, like every other
-- value the node uses.
function checker(inputs, outputs)
    local width  = inputs["width"].value
    local height = inputs["height"].value
    assert(width > 0 and height > 0, "width and height must be positive")
    assert(inputs["squareSize"].value > 0, "squareSize must be positive")

    outputs["Checker"] = cuda.image(width, height, cuda.uchar4)

    return cuda.kernel({
        args = {
            cuda.int(width),                        -- -> int width
            cuda.int(height),                       -- -> int height
            cuda.int(inputs["squareSize"]),         -- -> int squareSize
            cuda.array(inputs["colorA"]),           -- -> const float* colorA
            cuda.array(inputs["colorB"]),           -- -> const float* colorB
            cuda.SurfaceObject(outputs["Checker"]), -- -> cudaSurfaceObject_t output
        },
        block = { 16, 16 },
        grid  = { math.ceil(width / 16), math.ceil(height / 16) },
    })
end

Refer to Write a Node With No Input for what a node without an input can and cannot assume.