ggiOvlAttach extends a visual such that the LibOvl API may be used on the visual handle. This function must be called before using other LibOvl functions on the visual handle. The parameter reslist is a pointer to a LibGAlloc resource list kept by the application, and such an object must exist and be passed here in order to use the simple-form ggiOvlCreate* functions.
ggiOvlDetach cleans up all state associated with using the LibOvl API on this visual. The visual is stripped of any active LibOvl objects. Note, however, that the objects themselves are not currently guaranteed to be destroyed and may still exist, consuming resources. Behavior of these objects is at this point undefined. They should be destroyed before calling ggiOvlDetach.