diff --git a/src/AcDream.App/Input/PlayerMovementController.cs b/src/AcDream.App/Input/PlayerMovementController.cs
index b5b7466..01feaf4 100644
--- a/src/AcDream.App/Input/PlayerMovementController.cs
+++ b/src/AcDream.App/Input/PlayerMovementController.cs
@@ -15,7 +15,8 @@ public readonly record struct MovementInput(
     bool TurnLeft = false,
     bool TurnRight = false,
     bool Run = false,
-    float MouseDeltaX = 0f);
+    float MouseDeltaX = 0f,
+    bool Jump = false);
 
 /// <summary>
 /// Result of a single frame's movement update.
@@ -53,6 +54,12 @@ public sealed class PlayerMovementController
     /// </summary>
     public float StepUpHeight { get; set; } = 5.0f;
 
+    public float VerticalVelocity { get; private set; }
+    public bool IsAirborne { get; private set; }
+    public float JumpImpulse { get; set; } = 10f;
+    public float GravityAccel { get; set; } = 20f;
+    public float AirControlFactor { get; set; } = 0.2f;
+
     public float Yaw { get; set; }
     public Vector3 Position { get; private set; }
     public uint CellId { get; private set; }
@@ -104,11 +111,59 @@ public sealed class PlayerMovementController
         if (input.StrafeRight) { dx += rightX * speed * dt * 0.5f; dy += rightY * speed * dt * 0.5f; }
         if (input.StrafeLeft) { dx -= rightX * speed * dt * 0.5f; dy -= rightY * speed * dt * 0.5f; }
 
-        var delta = new Vector3(dx, dy, 0f);
+        // While airborne, reduce horizontal authority.
+        float airFactor = IsAirborne ? AirControlFactor : 1f;
+        var delta = new Vector3(dx * airFactor, dy * airFactor, 0f);
 
         // 3. Resolve via physics engine.
         var result = _physics.Resolve(Position, CellId, delta, StepUpHeight);
-        Position = result.Position;
+
+        // 4. Jump + gravity + falling (vertical axis).
+        float resolvedGroundZ = result.Position.Z;
+
+        // Initiate jump when grounded and Space pressed.
+        if (input.Jump && result.IsOnGround && !IsAirborne)
+        {
+            VerticalVelocity = JumpImpulse;
+            IsAirborne = true;
+        }
+
+        float newZ;
+        if (IsAirborne)
+        {
+            // Apply gravity and integrate vertical position.
+            VerticalVelocity -= GravityAccel * dt;
+            float candidateZ = Position.Z + VerticalVelocity * dt;
+
+            if (candidateZ <= resolvedGroundZ)
+            {
+                // Landed on terrain/floor.
+                newZ = resolvedGroundZ;
+                IsAirborne = false;
+                VerticalVelocity = 0f;
+            }
+            else
+            {
+                // Still airborne — override terrain Z with ballistic Z.
+                newZ = candidateZ;
+            }
+        }
+        else
+        {
+            // Detect walking off a ledge: terrain dropped more than StepUpHeight.
+            if (resolvedGroundZ < Position.Z - StepUpHeight)
+            {
+                IsAirborne = true;
+                VerticalVelocity = 0f;
+                newZ = Position.Z;  // stay at current Z this frame; gravity will pull us down next frame
+            }
+            else
+            {
+                newZ = resolvedGroundZ;
+            }
+        }
+
+        Position = new Vector3(result.Position.X, result.Position.Y, newZ);
         CellId = result.CellId;
 
         // 4. Determine current motion commands.
@@ -180,9 +235,9 @@ public sealed class PlayerMovementController
         }
 
         return new MovementResult(
-            Position: result.Position,
-            CellId: result.CellId,
-            IsOnGround: result.IsOnGround,
+            Position: Position,
+            CellId: CellId,
+            IsOnGround: !IsAirborne,
             MotionStateChanged: changed,
             ForwardCommand: forwardCmd,
             SidestepCommand: sidestepCmd,
diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 124edb4..ef0087e 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -1367,7 +1367,8 @@ public sealed class GameWindow : IDisposable
                 }
             }
 
-            _physicsEngine.AddLandblock(lb.LandblockId, terrainSurface, cellSurfaces, origin.X, origin.Y);
+            _physicsEngine.AddLandblock(lb.LandblockId, terrainSurface, cellSurfaces,
+                Array.Empty<AcDream.Core.Physics.PortalPlane>(), origin.X, origin.Y);
         }
 
         // Upload every GfxObj referenced by this landblock's entities.
@@ -1496,7 +1497,8 @@ public sealed class GameWindow : IDisposable
                 TurnLeft:    kb.IsKeyPressed(Key.A),
                 TurnRight:   kb.IsKeyPressed(Key.D),
                 Run:         kb.IsKeyPressed(Key.ShiftLeft) || kb.IsKeyPressed(Key.ShiftRight),
-                MouseDeltaX: consumedMouseDeltaX);
+                MouseDeltaX: consumedMouseDeltaX,
+                Jump:        kb.IsKeyPressed(Key.Space));
 
             var result = _playerController.Update((float)dt, input);
 
diff --git a/src/AcDream.Core/Physics/PhysicsEngine.cs b/src/AcDream.Core/Physics/PhysicsEngine.cs
index f36b704..802b470 100644
--- a/src/AcDream.Core/Physics/PhysicsEngine.cs
+++ b/src/AcDream.Core/Physics/PhysicsEngine.cs
@@ -27,17 +27,19 @@ public sealed class PhysicsEngine
     private sealed record LandblockPhysics(
         TerrainSurface Terrain,
         IReadOnlyList<CellSurface> Cells,
+        IReadOnlyList<PortalPlane> Portals,
         float WorldOffsetX,
         float WorldOffsetY);
 
     /// <summary>
-    /// Register a landblock with its terrain surface, indoor cells, and
-    /// world-space origin offset.
+    /// Register a landblock with its terrain surface, indoor cells, portal
+    /// planes, and world-space origin offset.
     /// </summary>
     public void AddLandblock(uint landblockId, TerrainSurface terrain,
-        IReadOnlyList<CellSurface> cells, float worldOffsetX, float worldOffsetY)
+        IReadOnlyList<CellSurface> cells, IReadOnlyList<PortalPlane> portals,
+        float worldOffsetX, float worldOffsetY)
     {
-        _landblocks[landblockId] = new LandblockPhysics(terrain, cells, worldOffsetX, worldOffsetY);
+        _landblocks[landblockId] = new LandblockPhysics(terrain, cells, portals, worldOffsetX, worldOffsetY);
     }
 
     /// <summary>
@@ -116,38 +118,92 @@ public sealed class PhysicsEngine
         // indoors" path and snaps Z to an EnvCell floor 28m below.
         bool currentlyIndoor = (cellId & 0xFFFFu) >= 0x0100;
 
-        if (currentlyIndoor && bestCellZ is not null)
+        if (currentlyIndoor)
         {
-            // Stay indoors on the best cell's floor.
-            targetZ = bestCellZ.Value;
-            targetCellId = bestCell!.CellId & 0xFFFFu;
+            // Check whether the player crosses a portal belonging to the current cell.
+            uint currentCellIndex = cellId & 0xFFFFu;
+            PortalPlane? crossedPortal = null;
+            foreach (var portal in physics.Portals)
+            {
+                // Only portals owned by the current cell are relevant when indoors.
+                if ((portal.OwnerCellId & 0xFFFFu) != currentCellIndex) continue;
+                if (portal.IsCrossing(currentPos, candidatePos))
+                {
+                    crossedPortal = portal;
+                    break;
+                }
+            }
+
+            if (crossedPortal is not null)
+            {
+                if (crossedPortal.Value.TargetCellId == 0xFFFFu)
+                {
+                    // Indoor → Outdoor exit.
+                    targetZ = terrainZ;
+                    targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
+                }
+                else
+                {
+                    // Indoor → Indoor (room to room).
+                    uint nextCellIndex = crossedPortal.Value.TargetCellId & 0xFFFFu;
+                    CellSurface? nextCell = null;
+                    foreach (var c in physics.Cells)
+                    {
+                        if ((c.CellId & 0xFFFFu) == nextCellIndex) { nextCell = c; break; }
+                    }
+                    float? nextFloorZ = nextCell?.SampleFloorZ(candidatePos.X, candidatePos.Y);
+                    targetZ = nextFloorZ ?? terrainZ;
+                    targetCellId = nextCellIndex;
+                }
+            }
+            else if (bestCellZ is not null)
+            {
+                // Staying in the same indoor cell.
+                targetZ = bestCellZ.Value;
+                targetCellId = bestCell!.CellId & 0xFFFFu;
+            }
+            else
+            {
+                // No cell floor found and no portal crossed — fall back to outdoor.
+                targetZ = terrainZ;
+                targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
+            }
         }
-        else if (currentlyIndoor && bestCellZ is null)
-        {
-            // Walked out of the current cell — transition to outdoor.
-            targetZ = terrainZ;
-            targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
-        }
-#pragma warning disable CS0162
-        else if (false)  // Phase B.2 MVP: outdoor→indoor transition DISABLED.
-        {
-            // 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.
-            targetZ = terrainZ;
-            targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
+            // Outdoor player: check for a portal crossing into an indoor cell.
+            // Outside-facing portals have TargetCellId == 0xFFFF (they face the
+            // outdoor world); crossing one from the outdoor side enters the OwnerCellId.
+            PortalPlane? crossedPortal = null;
+            foreach (var portal in physics.Portals)
+            {
+                if (portal.TargetCellId != 0xFFFFu) continue; // only outside-facing portals
+                if (portal.IsCrossing(currentPos, candidatePos))
+                {
+                    crossedPortal = portal;
+                    break;
+                }
+            }
+
+            if (crossedPortal is not null)
+            {
+                // Outdoor → Indoor: enter the OwnerCellId.
+                uint enterCellIndex = crossedPortal.Value.OwnerCellId & 0xFFFFu;
+                CellSurface? enterCell = null;
+                foreach (var c in physics.Cells)
+                {
+                    if ((c.CellId & 0xFFFFu) == enterCellIndex) { enterCell = c; break; }
+                }
+                float? enterFloorZ = enterCell?.SampleFloorZ(candidatePos.X, candidatePos.Y);
+                targetZ = enterFloorZ ?? terrainZ;
+                targetCellId = enterCellIndex;
+            }
+            else
+            {
+                // Stay outdoors on terrain.
+                targetZ = terrainZ;
+                targetCellId = physics.Terrain.ComputeOutdoorCellId(localCandX, localCandY);
+            }
         }
 
         // Step-height enforcement: block upward movement that exceeds the limit.
diff --git a/tests/AcDream.Core.Tests/Input/PlayerMovementControllerTests.cs b/tests/AcDream.Core.Tests/Input/PlayerMovementControllerTests.cs
index aceb1e1..643af37 100644
--- a/tests/AcDream.Core.Tests/Input/PlayerMovementControllerTests.cs
+++ b/tests/AcDream.Core.Tests/Input/PlayerMovementControllerTests.cs
@@ -17,7 +17,7 @@ public class PlayerMovementControllerTests
         for (int i = 0; i < 256; i++) heightTable[i] = i * 1f;
         var terrain = new TerrainSurface(heights, heightTable);
         engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
-            worldOffsetX: 0f, worldOffsetY: 0f);
+            Array.Empty<PortalPlane>(), worldOffsetX: 0f, worldOffsetY: 0f);
         return engine;
     }
 
@@ -100,4 +100,82 @@ public class PlayerMovementControllerTests
 
         Assert.True(result.MotionStateChanged);
     }
+
+    [Fact]
+    public void Update_JumpOnFlatTerrain_BecomesAirborne()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+
+        var input = new MovementInput(Jump: true);
+        controller.Update(0.016f, input);
+
+        Assert.True(controller.IsAirborne);
+        Assert.True(controller.VerticalVelocity > 0f);
+    }
+
+    [Fact]
+    public void Update_AirborneFrames_ZRiseThenFalls()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+
+        // Jump
+        controller.Update(0.016f, new MovementInput(Jump: true));
+        float z1 = controller.Position.Z;
+
+        // A few frames of rising
+        controller.Update(0.1f, new MovementInput());
+        float z2 = controller.Position.Z;
+        Assert.True(z2 > z1, "Should be rising");
+
+        // Many frames — should come back down
+        for (int i = 0; i < 30; i++)
+            controller.Update(0.05f, new MovementInput());
+
+        Assert.False(controller.IsAirborne, "Should have landed");
+        Assert.Equal(50f, controller.Position.Z, precision: 1);
+    }
+
+    [Fact]
+    public void Update_WalkOffLedge_BecomesFalling()
+    {
+        // Build terrain with a sharp cliff: grid x<5 = Z50, grid x>=5 = Z20.
+        // heights[x*9+y] is indexed x-major; heightTable[i]=i*1f so
+        // byte value == Z value directly.
+        var heights = new byte[81];
+        for (int x = 0; x < 9; x++)
+            for (int y = 0; y < 9; y++)
+                heights[x * 9 + y] = (byte)(x < 5 ? 50 : 20);
+
+        var heightTable = new float[256];
+        for (int i = 0; i < 256; i++) heightTable[i] = i * 1f;
+
+        var engine = new PhysicsEngine();
+        var terrain = new TerrainSurface(heights, heightTable);
+        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
+            Array.Empty<PortalPlane>(), worldOffsetX: 0f, worldOffsetY: 0f);
+
+        // Position the player just before the cliff edge (localX=118 ≈ grid x=4.92).
+        // At this point terrain Z is ~51.7 (bilinear interpolation near the high side).
+        // One step at walk speed will cross into the low region where terrain drops
+        // ~28 units — more than StepUpHeight=5, triggering the ledge-fall.
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(118f, 96f, 50f), 0x0001);
+        controller.Yaw = 0f; // facing +X
+
+        // Single step — should trigger airborne state because terrain drops sharply.
+        controller.Update(0.05f, new MovementInput(Forward: true));
+
+        Assert.True(controller.IsAirborne, "Player should be airborne after stepping off the cliff");
+
+        // Simulate enough frames to fall and land on the Z=20 floor.
+        for (int i = 0; i < 60; i++)
+            controller.Update(0.05f, new MovementInput(Forward: true));
+
+        Assert.False(controller.IsAirborne, "Player should have landed");
+        Assert.Equal(20f, controller.Position.Z, precision: 1);
+    }
 }
diff --git a/tests/AcDream.Core.Tests/Physics/PhysicsEngineTests.cs b/tests/AcDream.Core.Tests/Physics/PhysicsEngineTests.cs
index 543555c..d6e6e55 100644
--- a/tests/AcDream.Core.Tests/Physics/PhysicsEngineTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/PhysicsEngineTests.cs
@@ -26,7 +26,7 @@ public class PhysicsEngineTests
     {
         var engine = new PhysicsEngine();
         var terrain = new TerrainSurface(FlatHeightmap((byte)terrainZ), LinearHeightTable());
-        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
+        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
             worldOffsetX: 0f, worldOffsetY: 0f);
         return engine;
     }
@@ -55,7 +55,7 @@ public class PhysicsEngineTests
 
         var engine = new PhysicsEngine();
         var terrain = new TerrainSurface(heights, LinearHeightTable());
-        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
+        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
             worldOffsetX: 0f, worldOffsetY: 0f);
 
         var result = engine.Resolve(
@@ -77,7 +77,7 @@ public class PhysicsEngineTests
 
         var engine = new PhysicsEngine();
         var terrain = new TerrainSurface(heights, LinearHeightTable());
-        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
+        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
             worldOffsetX: 0f, worldOffsetY: 0f);
 
         // Try to walk from the low side to the high side.
@@ -91,40 +91,105 @@ public class PhysicsEngineTests
     }
 
     [Fact]
-    public void Resolve_EnterIndoorCell_StaysOutdoor_BecauseTransitionDisabled()
+    public void Resolve_OutdoorThroughPortal_TransitionsToIndoor()
+    {
+        var engine = new PhysicsEngine();
+        var terrain = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
+
+        // A CellSurface for the indoor cell with floor at Z=50.
+        var cellVerts = new Dictionary<ushort, Vector3>
+        {
+            [0] = new(40f, 40f, 50f),
+            [1] = new(60f, 40f, 50f),
+            [2] = new(60f, 60f, 50f),
+            [3] = new(40f, 60f, 50f),
+        };
+        var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
+        var cell = new CellSurface(0x0100, cellVerts, cellPolys);
+
+        // A portal plane at X=45 (vertical plane facing +X).
+        // OwnerCellId = 0x0100 (the indoor cell), TargetCellId = 0xFFFF (faces outdoor).
+        // From outside, walking through this portal enters OwnerCellId.
+        var portal = PortalPlane.FromVertices(
+            new Vector3(45f, 40f, 45f),
+            new Vector3(45f, 60f, 45f),
+            new Vector3(45f, 60f, 55f),
+            targetCellId: 0xFFFF, ownerCellId: 0x0100, flags: 0);
+
+        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, new[] { portal },
+            worldOffsetX: 0f, worldOffsetY: 0f);
+
+        // Walk from X=40 (outdoor) through X=45 (portal) to X=50 (indoor).
+        var result = engine.Resolve(
+            new Vector3(40f, 50f, 50f), cellId: 0x0001, delta: new Vector3(10f, 0f, 0f),
+            stepUpHeight: 5f);
+
+        // Should have transitioned to indoor cell 0x0100.
+        Assert.Equal(0x0100u, result.CellId & 0xFFFFu);
+        Assert.True(result.IsOnGround);
+    }
+
+    [Fact]
+    public void Resolve_IndoorThroughExitPortal_TransitionsToOutdoor()
     {
-        // Phase B.2 MVP: outdoor→indoor transitions are disabled because
-        // CellSurface floor polygons are too aggressive (building
-        // footprints/roofs capture the player). Walking over a cell's XY
-        // area stays on the outdoor terrain Z. Indoor transitions will be
-        // re-enabled when portal-based detection lands in Phase E.
         var engine = new PhysicsEngine();
         var terrain = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
 
         var cellVerts = new Dictionary<ushort, Vector3>
         {
-            [0] = new(40f, 40f, 55f),
-            [1] = new(60f, 40f, 55f),
-            [2] = new(60f, 60f, 55f),
-            [3] = new(40f, 60f, 55f),
+            [0] = new(40f, 40f, 50f),
+            [1] = new(60f, 40f, 50f),
+            [2] = new(60f, 60f, 50f),
+            [3] = new(40f, 60f, 50f),
         };
         var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
         var cell = new CellSurface(0x0100, cellVerts, cellPolys);
 
-        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell },
+        // Same portal geometry — OwnerCellId = 0x0100, TargetCellId = 0xFFFF (outdoor exit).
+        var portal = PortalPlane.FromVertices(
+            new Vector3(45f, 40f, 45f),
+            new Vector3(45f, 60f, 45f),
+            new Vector3(45f, 60f, 55f),
+            targetCellId: 0xFFFF, ownerCellId: 0x0100, flags: 0);
+
+        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, new[] { portal },
             worldOffsetX: 0f, worldOffsetY: 0f);
 
-        // Walk from outdoor (30, 50) into the cell's floor area (50, 50).
+        // Walk from X=50 (indoor) through X=45 (portal) to X=40 (outdoor).
         var result = engine.Resolve(
-            new Vector3(30f, 50f, 50f), cellId: 0x0001, delta: new Vector3(20f, 0f, 0f),
-            stepUpHeight: 10f);
+            new Vector3(50f, 50f, 50f), cellId: 0x0100, delta: new Vector3(-10f, 0f, 0f),
+            stepUpHeight: 5f);
 
-        // Should stay outdoor (transition disabled) at terrain Z = 50.
-        Assert.True(result.CellId < 0x0100u);
-        Assert.Equal(50f, result.Position.Z, precision: 1);
+        // Should have transitioned to outdoor.
+        Assert.True((result.CellId & 0xFFFFu) < 0x0100u);
         Assert.True(result.IsOnGround);
     }
 
+    [Fact]
+    public void Resolve_LandblockBoundary_PicksAdjacentTerrain()
+    {
+        var engine = new PhysicsEngine();
+
+        // Landblock A: flat at Z=50, offset at X=0.
+        var terrainA = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
+        engine.AddLandblock(0xA9B4FFFFu, terrainA, Array.Empty<CellSurface>(),
+            Array.Empty<PortalPlane>(), worldOffsetX: 0f, worldOffsetY: 0f);
+
+        // Landblock B: flat at Z=60, offset at X=192 (adjacent east).
+        var terrainB = new TerrainSurface(FlatHeightmap(60), LinearHeightTable());
+        engine.AddLandblock(0xAAB4FFFFu, terrainB, Array.Empty<CellSurface>(),
+            Array.Empty<PortalPlane>(), worldOffsetX: 192f, worldOffsetY: 0f);
+
+        // Walk from X=190 (landblock A) across to X=194 (landblock B).
+        var result = engine.Resolve(
+            new Vector3(190f, 96f, 50f), cellId: 0x0001, delta: new Vector3(4f, 0f, 0f),
+            stepUpHeight: 15f);
+
+        // Should be at Z=60 (landblock B's terrain) and position X≈194.
+        Assert.Equal(60f, result.Position.Z, precision: 1);
+        Assert.True(result.Position.X > 192f);
+    }
+
     [Fact]
     public void Resolve_LeaveIndoorCell_TransitionsToOutdoor()
     {
@@ -141,7 +206,7 @@ public class PhysicsEngineTests
         var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
         var cell = new CellSurface(0x0100, cellVerts, cellPolys);
 
-        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell },
+        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, Array.Empty<PortalPlane>(),
             worldOffsetX: 0f, worldOffsetY: 0f);
 
         // Start inside the cell, walk out.