Function ncvisual_from_plane 

pub unsafe extern "C" fn ncvisual_from_plane(
    n: *const ncplane,
    blit: ncblitter_e,
    begy: c_int,
    begx: c_int,
    leny: c_uint,
    lenx: c_uint,
) -> *mut ncvisual

Promote an ncplane ‘n’ to an ncvisual. The plane may contain only spaces, half blocks, and full blocks. The latter will be checked, and any other glyph will result in a NULL being returned. This function exists so that planes can be subjected to ncvisual transformations. If possible, it’s better to create the ncvisual from memory using ncvisual_from_rgba(). Lengths of 0 are interpreted to mean “all available remaining area”.