Function gtk_symbolic_paintable_snapshot_with_weight 

pub unsafe extern "C" fn gtk_symbolic_paintable_snapshot_with_weight(
    paintable: *mut GtkSymbolicPaintable,
    snapshot: *mut GdkSnapshot,
    width: c_double,
    height: c_double,
    colors: *const GdkRGBA,
    n_colors: size_t,
    weight: c_double,
)

Available on crate feature v4_22 only.