Function offset_face 

pub fn offset_face(
    topo: &mut Topology,
    face_id: FaceId,
    distance: f64,
    samples: usize,
) -> Result<FaceId, OperationsError>

Create a new face that is offset from face_id by distance along the outward surface normal.

Positive distance offsets outward (away from the solid interior), negative distance offsets inward.

For planar faces, the operation is exact. For NURBS faces, the surface is sampled at a grid of samples × samples points and re-interpolated.

Errors

Returns an error if:

• The face lookup fails
• NURBS surface normal computation fails at any sample point
• Surface re-interpolation fails