feat(render) Campaign FW1: port the exact retail degrade selection

UpdateViewerDistance @0x0050e030 + get_degrade @0x0051e4b0 ported with
live-pinned globals: distance measured to the part SCALED SORT CENTER,
effective = max(0, dist - s_rDegradeDistance [live 100]), level = first
with effective < IdealDist (the live auto_update_deg_mul<=0 arm), else
the last level. WalkBuildingDegradeLevel carries the full authored
bands; the adapter fills sort centers; the replay context measures to
the transformed sort center. Sweep state after the rule: the level-0
building set is now correct; the residual divergence is the per-portal
side/clip gate (my arms punch a near-complement of retail two) - the
sweep driver carries the next instrument in its Skip note.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/Rendering/Walk/WalkBuilding.cs

@@ -38,8 +38,9 @@ public sealed class WalkBspNode
 }
 
 /// <summary>One degrade-ladder level: the drawing BSP of that level's
-/// GfxObj (portal-only view) and the level's far distance bound.</summary>
+/// GfxObj (portal-only view) and the level's authored distance bands.</summary>
-public readonly record struct WalkBuildingDegradeLevel(float MaxDist, WalkBspNode? DrawingBsp);
+public readonly record struct WalkBuildingDegradeLevel(
+    float MinDist, float IdealDist, float MaxDist, WalkBspNode? DrawingBsp);
 
 /// <summary>The walk's building model (retail <c>CBuildingObj</c> +
 /// <c>BuildInfo</c> as the frame walk consumes them).</summary>
@@ -66,19 +67,36 @@ public sealed class WalkBuilding
     /// skips the whole building AFTER publishing the portal list.</summary>
     public bool HasGeometry = true;
 
-    /// <summary>Level selection by viewer distance. Simplified band pick
+    /// <summary>The base GfxObj's sort center — retail measures the viewer
-    /// (first level whose MaxDist covers the distance) — the faithful
+    /// distance to the part's SCALED sort center, not the position origin
-    /// hysteresis of <c>CPhysicsPart::UpdateViewerDistance</c> is a port
+    /// (<c>CPhysicsPart::UpdateViewerDistance</c> @0x0050e030).</summary>
-    /// TODO; still fixtures are insensitive to hysteresis.</summary>
+    public Vector3 SortCenter;
-    public WalkBspNode? SelectDrawingBsp(float viewerDistance)
+
+    /// <summary>Retail <c>Render::s_rDegradeDistance</c> — a subtractive
+    /// slack before the ladder applies (live-dumped 100 on the capture
+    /// client; registry-configurable).</summary>
+    public const float DefaultDegradeDistance = 100f;
+
+    /// <summary>
+    /// <c>GfxObjDegradeInfo::get_degrade</c> @0x0051e4b0 (the live client's
+    /// arm: <c>auto_update_deg_mul</c> with a non-positive multiplier →
+    /// thresholds are the levels' IDEAL distances): effective =
+    /// max(0, distance − degradeDistance); the FIRST level with
+    /// effective &lt; IdealDist wins; no match → the LAST level. The
+    /// positive-bias arm (threshold = ideal − (ideal−max)·mul) is a port
+    /// follow-up if a fixture ever pins a positive bias.
+    /// </summary>
+    public WalkBspNode? SelectDrawingBsp(
+        float viewerDistance, float degradeDistance = DefaultDegradeDistance)
     {
         if (DegradeLevels.Length == 0) return DrawingBsp;
+        float effective = MathF.Max(0f, MathF.Abs(viewerDistance) - degradeDistance);
         foreach (WalkBuildingDegradeLevel level in DegradeLevels)
         {
-            if (viewerDistance <= level.MaxDist)
+            if (effective < level.IdealDist)
                 return level.DrawingBsp;
         }
-        return null;   // degraded out entirely
+        return DegradeLevels[^1].DrawingBsp;
     }
 }
 

tests/AcDream.App.Tests/Rendering/Walk/WalkLookInGateSweepTests.cs

@@ -24,12 +24,14 @@ public sealed class WalkLookInGateSweepTests
         public void Emit(in WalkEvent walkEvent) => Events.Add(walkEvent);
     }
 
-    [Fact(Skip = "FW1 adjudication driver (2026-08-30 state): the degrade-level "
+    [Fact(Skip = "FW1 adjudication driver (2026-08-30 final state): with the "
-        + "BSP gate killed every wrong punch — remaining deltas are the near "
+        + "exact get_degrade rule (slack 100, ideal thresholds, sort-center "
-        + "buildings 001a/0022 (50/28 m center distance vs the 48 m level-0 "
+        + "distance) the level-0 set is correct — the residual divergence is "
-        + "band: port UpdateViewerDistance's sphere-adjusted distance + "
+        + "the per-portal side/clip gate: my arms punch {0017,001e,0026,0036}, "
-        + "hysteresis) and the ring-1 frustum boundary pair "
+        + "retail punched exactly {001a,0022} — a near-complement suggesting "
-        + "(aab50002 extra / a9b3003c missing). Re-enable to re-adjudicate.")]
+        + "one more polarity at the building-portal gate. Next instrument: "
+        + "per-portal dump for 001a (retail punches) vs 001e (retail doesn't): "
+        + "side values, plane orientation, eye side, clip result per arm.")]
     public void Sweep_the_lookin_gate_decodes_against_the_street_fixture()
     {
         string? datDir = CornerFloodReplayTests.ResolveDatDir();

tests/AcDream.App.Tests/Rendering/Walk/WalkTraceReplay.cs

@@ -114,7 +114,8 @@ public sealed class WalkTraceReplayContext : IWalkFrameContext, IRetailFrameWalk
 
     public float ViewerDistanceTo(WalkBuilding building)
         => Vector3.Distance(
-            WorldViewpoint, Buildings[building].WorldTransform.Translation);
+            WorldViewpoint,
+            Vector3.Transform(building.SortCenter, Buildings[building].WorldTransform));
 
     public int ClipBuildingPolygon(
         WalkBuilding building, WalkPolygon polygon, int side, Span<WalkScreenPoint> output)

tests/AcDream.App.Tests/Rendering/Walk/WalkWorldDatAdapter.cs

@@ -148,10 +148,12 @@ public static class WalkWorldDatAdapter
             }
 
             WalkBspNode? bsp = null;
+            Vector3 sortCenter = Vector3.Zero;
             var degradeLevels = new List<WalkBuildingDegradeLevel>();
             if (dats.Get<GfxObj>(buildingInfo.ModelId) is GfxObj gfxObj)
             {
                 bsp = ConvertDrawingBsp(gfxObj, gfxObj.DrawingBSP?.Root);
+                sortCenter = new Vector3(gfxObj.SortCenter.X, gfxObj.SortCenter.Y, gfxObj.SortCenter.Z);
                 if (gfxObj.DIDDegrade != 0
                     && dats.Get<GfxObjDegradeInfo>(gfxObj.DIDDegrade)
                         is GfxObjDegradeInfo degradeInfo)
@@ -164,7 +166,7 @@ public static class WalkWorldDatAdapter
                         {
                             levelBsp = ConvertDrawingBsp(levelGfx, levelGfx.DrawingBSP?.Root);
                         }
-                        degradeLevels.Add(new WalkBuildingDegradeLevel(level.MaxDist, levelBsp));
+                        degradeLevels.Add(new WalkBuildingDegradeLevel(level.MinDist, level.IdealDist, level.MaxDist, levelBsp));
                     }
                 }
             }
@@ -180,6 +182,7 @@ public static class WalkWorldDatAdapter
                     Portals = portals,
                     DrawingBsp = bsp,
                     DegradeLevels = degradeLevels.ToArray(),
+                    SortCenter = sortCenter,
                 },
                 worldTransform,
                 inverse));