Function build_texture_index 

pub fn build_texture_index(
    content: &[u8],
    decoder: &mut EntityDecoder<'_>,
) -> FxHashMap<u32, ResolvedTextureMap>

Scan the model for IfcIndexedTriangleTextureMap entities and build an index keyed by the face set id each one maps to (issue #961). Cheap substring bail-out keeps untextured files (the overwhelming majority) off the scan.