cairo/surface.go
func (v *Surface) native() *C.cairo_surface_t {
	if v == nil {
		return nil
	}
	return v.surface
}
func (v *Surface) native() *C.cairo_surface_t {
	if v == nil {
		return nil
	}
	return v.surface
}
// native returns a pointer to the underlying cairo_surface_t.