Function write_obj 

pub fn write_obj(
    topo: &Topology,
    solids: &[SolidId],
    deflection: f64,
) -> Result<String, IoError>

Write one or more solids to OBJ format as a UTF-8 string.

Tessellates each solid’s faces and writes all triangles into a single OBJ file. The deflection parameter controls tessellation quality.

Errors

Returns an error if tessellation fails.