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Root API Migration to URootUi

URootUi is now the canonical public root API.

Old to New Mapping

  • UScreenRoot -> URootUi::screen()
  • UWorldRoot { size, is_3d: false } -> URootUi::world_2d(size)
  • UWorldRoot { size, is_3d: true } -> URootUi::world_3d(size)

Important Semantic Changes

  • URootUi::screen() is a real viewport-fixed HUD root.
  • URootUi roots are closed stacking capsules.
  • UVal::Px means logical UI units, not literal monitor pixels.
  • world-space physical size is controlled by meters_per_unit.

Legacy Compatibility Notes

  • UScreenRoot and UWorldRoot remain deprecated compatibility wrappers.
  • They are explicit-only migration paths and are no longer part of the recommended prelude story.
  • The current removal target is the first alpha after 0.3.0 that no longer needs wrapper-based migration support.
  • Set meters_per_unit explicitly when you need a specific physical world-root size.