When Unity drops support for an old LTS version, the ability to maintain or emulate those games goes with it. The leak allows preservationists to document the internal logic of deprecated components. If a game from 2017 relies on a specific shader compiler bug, preservationists can now emulate that bug faithfully because they have the original logic. As one archivist put it, "This is the Rosetta Stone for 2020s PC gaming."
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Using Unity source code to make a new engine - is it possible? When Unity drops support for an old LTS