From 3b2f56c531c7a7e25e877ca8235ca5d9fe7735e9 Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Sun, 12 Apr 2026 15:08:36 +0200
Subject: [PATCH] =?UTF-8?q?fix(core):=20Phase=20B.2=20MVP=20=E2=80=94=20di?=
 =?UTF-8?q?sable=20outdoor=E2=86=92indoor=20transition=20entirely?=
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Three attempts at guarding the indoor transition (cellId mask,
Z threshold, terrainZ comparison) all failed because CellSurface
floor polygons are too aggressive — building footprints, roofs, and
upper floors all have PhysicsPolygons that cover wide XY areas at
various Z levels, and ANY outdoor position near a building matches
a cell floor. The proper solution is portal-based transition
(CellPortal boundary crossing), not floor-polygon containment —
but that's Phase E scope.

For the B.2 MVP: outdoor players NEVER transition to indoor cells.
The else-if branch is compiled out with `if (false)`. Indoor→outdoor
transition (walking OUT of a building) is also effectively disabled
since you can't get indoors in the first place. Walking on outdoor
terrain works correctly; walking into buildings will be blocked by
the terrain heightmap (you walk on the roof-level terrain, not
through the building).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/AcDream.Core/Physics/PhysicsEngine.cs | 27 ++++++++++-------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/src/AcDream.Core/Physics/PhysicsEngine.cs b/src/AcDream.Core/Physics/PhysicsEngine.cs
index 4f2b8dd..f36b704 100644
--- a/src/AcDream.Core/Physics/PhysicsEngine.cs
+++ b/src/AcDream.Core/Physics/PhysicsEngine.cs
@@ -128,24 +128,21 @@ public sealed class PhysicsEngine
             targetZ = terrainZ;
             targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
         }
-        else if (!currentlyIndoor && bestCellZ is not null
-                 && MathF.Abs(bestCellZ.Value - currentPos.Z) < stepUpHeight + 2f
-                 && bestCellZ.Value < terrainZ - 1f)
+#pragma warning disable CS0162
+        else if (false)  // Phase B.2 MVP: outdoor→indoor transition DISABLED.
         {
-            // Walked into an indoor cell from outdoor — transition to indoor.
-            // The extra guard `bestCellZ < terrainZ - 1` prevents transitioning
-            // into cells whose floor is AT or ABOVE terrain level — those are
-            // typically roofs, upper floors, or building footprints that overlap
-            // the outdoor terrain. A genuine indoor transition is into a cell
-            // whose floor is BELOW the terrain surface (basements, ground floors
-            // of buildings that sit on elevated terrain). Without this guard,
-            // standing near any building with a floor polygon covering the
-            // player's XY triggers an indoor transition and snaps Z to the
-            // cell's floor — which for multi-story buildings can be 30+ units
-            // below the outdoor terrain.
-            targetZ = bestCellZ.Value;
+            // The CellSurface floor polygons are too aggressive — building
+            // footprints, roofs, and upper floors all have physics polygons
+            // that cover wide XY areas at various Z levels. Any outdoor
+            // position near a building matches a cell floor, and the engine
+            // snaps into it regardless of how far below the terrain the
+            // floor actually is. Proper indoor transition requires portal
+            // detection (CellPortal boundary crossing), not floor-polygon
+            // containment. Disabled until Phase E implements that.
+            targetZ = bestCellZ!.Value;
             targetCellId = bestCell!.CellId & 0xFFFFu;
         }
+#pragma warning restore CS0162
         else
         {
             // Stay outdoors on terrain.