Get USD Attribute/Primvar

The read side of the pack's attribute story. Get USD Attribute pulls a single attribute - or a primvar - off a prim and hands it to you as a value you can inspect, wire around, or feed back into the pack. Where SetUSDAttribute writes, this reads. If you're debugging a stage ("what does this mesh's displayColor actually resolve to?") or building a graph that makes decisions based on a prim's data, this is the node.

There's a subtlety in the name: "primvar" is USD's term for a per-vertex or per-face attribute that travels with geometry - texture coordinates (primvars:st), colors (primvars:displayColor), normals. The is_primvar toggle is what makes this node smart about them, and it's on by default for a reason: if the plain attribute name isn't found, the node retries with the primvars: prefix prepended. So asking for st with is_primvar on finds primvars:st without you typing the prefix.

The inputs

• USD and prim_path (default /Root/Mesh) - what to read from.
• attribute_name - the attribute, e.g. points, displayColor, focalLength. Default myAttribute is a placeholder.
• is_primvar - boolean, default on; controls the primvars: fallback described above.

Output: a single * (wildcard/ANY) socket named value. This is ComfyUI's escape-hatch type - it can connect to anything, which is both the feature and the trap: it's up to whatever you plug it into to understand what it's receiving.

What actually comes out

The node returns a JSON string shaped like {"data": <value>, "type": "color3f"} - the value plus its USD type token. That shape is exactly what the pack's SetUSDAttribute expects to consume, so the natural loop is Get → (transform if you want) → Set. Into a generic ComfyUI node, though, it's a JSON blob and nothing more; don't expect a plain number out of it.

If the prim or attribute doesn't exist, you get a warning in the console and a None out - no crash. That's useful for optional reads, but it also means a typo silently propagates None downstream instead of erroring loudly.

Install & caveats

Pack install: ComfyUI Manager → search "ComfyUI-OpenUSD", or

cd ComfyUI/custom_nodes
git clone https://github.com/cjhosken/ComfyUI-OpenUSD

then restart. Deps: usd-core==26.5, numpy==2.5.0, trimesh.

Caveats: the USD socket is pack-private, the wildcard output only carries meaning for consumers that understand the JSON contract, and None-on-missing means you should check the console warnings when a read looks wrong. If you're reading a value that a lower layer defines, note this returns the resolved value - composition is already applied, which is usually what you want.