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fix(physics): Stage 1 — verbatim ordered-CELLARRAY membership pick (the R1 flap)

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Port CObjCell::find_cell_list (acclient_2013_pseudo_c.txt:308742) faithfully:
- build candidates into an ordered CellArray with the CURRENT cell at index 0
  (add_cell @308766);
- EXPAND via a single forward walk over the growing array, mirroring retail's
  for(i=0;i<num_cells;i++) cells[i].find_transit_cells loop (308775-308785),
  replacing the order-losing Queue/visited BFS;
- PICK in array order with interior-wins-break (308788-308825): current cell at
  index 0 wins a boundary straddle, so membership no longer ping-pongs.

Deletes the 5ca2f44 current-first pre-check (the ordered array subsumes it for every
seed). Keeps its guard test (TwoOverlappingCells_CurrentCellWinsTheStraddle) + adds
two conformance tests (current-cell-first ordering; interior-wins over outdoor
fallback). Membership net: 45 pass. Decomp finding: retail stability is emergent from
the ordered pick + carried seed, not a separate portal-crossing detector — see
docs/research/2026-06-03-cell-membership-ordered-cellarray-pseudocode.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-06-03 09:00:12 +02:00
parent bc56545634
commit 22a184ca68
2 changed files with 110 additions and 90 deletions
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47
tests/AcDream.Core.Tests/Physics/CellTransitFindCellSetTests.cs
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@ -202,4 +202,51 @@ public class CellTransitFindCellSetTests
Assert.Contains(otherCellId, cellSet);
Assert.Equal(currentCellId, containing); // retail current-cell-first hysteresis
}
// The ordered-CELLARRAY contract: FindCellSet returns the candidate set in
// retail add-order with the CURRENT cell at index 0 (retail add_cell @308766).
// This is the invariant the verbatim pick relies on; the unordered HashSet
// could not guarantee it.
[Fact]
public void FindCellSet_CurrentCellIsFirstInTheSet()
{
var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 0);
var cellBT = Matrix4x4.CreateTranslation(new Vector3(5f, 0f, 0f));
Matrix4x4.Invert(cellBT, out var cellBInv);
var cellB = new CellPhysics
{
WorldTransform = cellBT,
InverseWorldTransform = cellBInv,
Resolved = new Dictionary<ushort, ResolvedPolygon>(),
CellBSP = new CellBSPTree { Root = new CellBSPNode { Type = BSPNodeType.Leaf } },
};
var cache = new PhysicsDataCache();
cache.RegisterCellStructForTest(0xA9B40100u, cellA);
cache.RegisterCellStructForTest(0xA9B40101u, cellB);
// Straddle the portal plane so both cells are in the set.
var sphereCenter = new Vector3(2.0f, 0f, 2.5f);
CellTransit.FindCellSet(cache, sphereCenter, 0.5f, 0xA9B40100u, out var cellSet);
Assert.Equal(0xA9B40100u, cellSet.First()); // current cell at index 0
}
// Interior-wins over the outdoor fallback: while an interior cell still
// contains the centre, it wins even though the exit portal also added the
// outdoor landcell to the set (retail interior-wins-break, pc:308814-308819).
[Fact]
public void IndoorWithExitPortal_InteriorWinsWhileItContainsCentre()
{
// Interior cell at the landblock origin with an exit portal at local x=2.5;
// Leaf BSP contains any point. Centre at local (0,12,2.5) is INSIDE the cell
// and NOT across the exit plane, so interior must win even though the head
// sphere / exit logic may add the outdoor landcell.
var exitCell = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0xFFFF, flags: 0);
var cache = new PhysicsDataCache();
cache.RegisterCellStructForTest(0xA9B40100u, exitCell);
var sphereCenter = new Vector3(0f, 12f, 2.5f);
uint containing = CellTransit.FindCellSet(cache, sphereCenter, 0.5f, 0xA9B40100u, out _);
Assert.Equal(0xA9B40100u, containing); // interior-wins, not the outdoor landcell
}
}