Preserve imported geometry normals when using Vertex Color lighting

[Copilot]

Imported geometry could lose its intended shading when Lighting Mode = Vertex Color: shared-color meshes collapsed sharp edges into fully smooth normals, while face-corner-colored meshes preserved every split and broke smooth surfaces. The problem was not in import itself, but in the later vertex merge step that rebuilt room/compiler geometry.

• Root cause

  • Imported geometry vertices were being merged too aggressively after import.
  • The merge key ignored imported normals, and in the classic path it also relied on an unused Color field instead of the actual packed lighting data.

• What changed

  • Classic room rebuild path
    • Preserve transformed imported normals on tr_room_vertex.
    • Make imported-geometry deduplication compare:
      • position
      • packed lighting fields
      • attributes
      • transformed normal
  • Classic compiler path
    • Apply the same normal-preserving merge criteria during compiled room generation.
  • TombEngine compiler path
    • Include transformed normals in imported-geometry vertex merging, alongside position/color/double-sided state.

• Effect on shading

  • Vertices only merge when both lighting data and normals match.
  • Split normals remain split across sharp edges.
  • Shared normals remain shared across curved surfaces.
  • Existing SharpEdges behavior stays unchanged.

• Representative change

  existingIndex = roomVertices.IndexOf(v =>
      v.Position == trVertex.Position &&
      v.Lighting1 == trVertex.Lighting1 &&
      v.Attributes == trVertex.Attributes &&
      v.Lighting2 == trVertex.Lighting2 &&
      v.Normal == trVertex.Normal);

• Scope

  • Limited to imported-geometry vertex merge logic in the editor/runtime compile paths.
  • No changes to importer formats, lighting mode UI, or shader behavior.