Byte offset of vfunc_name in ns.class_name's class struct, from the loaded typelib (g-ir-compiler computed it; cached). A missing namespace / class / field is a consumer stub-generation bug — fatal, same as Live.Callback invariants.
| ns |
typelib namespace (Clutter) |
| class_name |
class name (Actor) |
| vfunc_name |
vfunc field name (get_preferred_width) |