Use Custom Mesh Attributes for SubdivisionSchema ... Chaser vs Adaptor ?

[SebSchmidtWetaFx]

Hi,

We've been using “mayaUsdExport” for a while using our internal export chasers, however I recently discovered a case where using the "adaptor" instead of "chasers" would make more sense. That said, I might have misunderstood the adaptor concept.

Due to legacy reasons our geometry does not use the USD_ATTR_subdivisionScheme attribute to describe what subdivision scheme is used. It rather uses a boolean (isSubd) which indicates that something should be using the CatmullClark subdivisionScheme:

bool MeshToUsd::isSubd()
{
    bool isSubd = m_dagFn.hasAttribute( "isSubd" );
    if ( !isSubd ) {
        return false;
    }
    /// check the value of 'isSubd'.........
}

example of geo

# create a cube
result = cmds.polyCube()
# get the shape
shape = cmds.listRelatives(result[0], children=True, fullPath=True)[0]
# add isSubd attribute
cmds.addAttr(shape, longName= "isSubd", at ="bool")
cmds.setAttr("{}.isSubd".format(shape), True )

The only way I found to support this was using our chaser and as part of the PostExport() to check all maya-mesh nodes for the mentioned isSubd attribute and set the subdivisionScheme on the UsdPrim accordingly:

void MeshToUsd::PostProcess()
{
    UsdGeomMesh mesh( prim );
    const TfToken subdiv = isSubd() ? UsdGeomTokens->catmullClark : UsdGeomTokens->none;
    mesh.CreateSubdivisionSchemeAttr( VtValue( subdiv ) );
    ...........
}

Where this is causing issues is where I want to get the Normals exported for nodes that are meshes, as we are not using the 'USD_ATTR_subdivisionScheme' attribute there is nothing that triggers the relevant code-path within mayaUsdExport and we're not getting Normals exported (even when setting USD_EmitNormals).

While I can work around this and add the Normals export into the chaser-logic, I am wondering if there is a better way of achieving the same result (without changing the scene) but using Adaptors?

Thank you for your insight!
Seb

FYI: @HamedSabri-adsk