So we know Vivillon's pattern depends on the geographical location set on the 3DS when the game was started. Once a save file exists, it will always yield the same Vivillon pattern even if the location on the 3DS is changed or the cartridge is played in a different 3DS. Trading the Scatterbug or Spewpa will retain the pattern, so it's a property set at some point during the creation of the Pokémon that doesn't change when it's traded even before it evolves.
Now my question is, when exactly is this property set when the Pokémon is created through breeding? Does the pattern depend on the save file the Pokémon was hatched in or is it already set when the Egg is created?
I'll add an example to illustrate what I mean:
Let's say my save file yields the Meadow pattern and I have a friend whose save file yields the Continental pattern. In my game, I breed a Scatterbug, get the Egg, and trade it to said friend. My friend then proceeds to hatch the Egg and evolve the Scatterbug. Will the resulting Vivillon now have the Meadow or Continental pattern?