passages: floor profile by nearest centreline + metric distance outside voids (L114, v222) - WIP

Floor ribs are present in L109/L112/L113 rock tunnels too: the floor height comes from the
nearest segment, so it jumps (up to 5.9-7.3 cm) where the nearest segment switches. v222 reduces
them; faint ribs remain. Quiet-machine timing (load 0.64): near-ready 9-17% slower than L109
(FI W12 0.95 -> 1.10 s); candidate totals ~5x L109. Fast tier FAIL: 2 SW wall-shell probes of
31,381 read host air. Walk/grade audits pass; Clang/GCC deterministic; UE builds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Core/src/ShapeWorldInternal.h

@@ -266,8 +266,10 @@ public:
             double roundSignedDistance=std::numeric_limits<double>::infinity();
             double centerZSubvoxels=0.0,floorCenterZSubvoxels=0.0;
             double radiusSubvoxels=0.0,floorDepthSubvoxels=0.0;
-            double t=0.0;
+            double floorCenterDistanceSq=std::numeric_limits<double>::infinity();
+            double t=0.0,floorT=0.0;
             std::uint32_t segmentIndex=std::numeric_limits<std::uint32_t>::max();
+            std::uint32_t floorSegmentIndex=std::numeric_limits<std::uint32_t>::max();
             float wallRelief=0.0f;
             bool valid=false,hasWallRelief=false;
         };
@@ -1216,8 +1218,9 @@ public:
             double signedDistance=std::numeric_limits<double>::infinity();
             double shellSignedDistance=std::numeric_limits<double>::infinity();
             double roundSignedDistance=std::numeric_limits<double>::infinity();
-            double centerZ=0.0,floorCenterZ=0.0,radius=0.0,floorDepth=0.0,t=0.0;
-            std::size_t segmentIndex=0;
+            double centerZ=0.0,floorCenterZ=0.0,radius=0.0,floorDepth=0.0;
+            double t=0.0,floorT=0.0;
+            std::size_t segmentIndex=0,floorSegmentIndex=0;
             bool valid=false;
             const FScopedPassageTileQueries::FPassageSweepSample* swept=nullptr;
         };
@@ -1255,6 +1258,8 @@ public:
                 nearest.floorCenterZ=swept->floorCenterZSubvoxels;
                 nearest.radius=swept->radiusSubvoxels;
                 nearest.floorDepth=swept->floorDepthSubvoxels;
+                nearest.floorSegmentIndex=swept->floorSegmentIndex;
+                nearest.floorT=swept->floorT;
                 nearest.valid=true;
                 nearest.swept=swept;
             }
@@ -1273,6 +1278,7 @@ public:
                 const std::ptrdiff_t lastIndex=static_cast<std::ptrdiff_t>(
                     PassageSegmentData[passageIndex].size())-1;
                 double bestDistance=std::numeric_limits<double>::infinity();
+                double bestFloorCenterDistanceSq=std::numeric_limits<double>::infinity();
                 const auto visitSegment=[&](std::size_t segmentIndex,int)
                 {
                     if(passageProfile)++passageProfile->passageCarveSegmentVisits;
@@ -1289,6 +1295,7 @@ public:
                     const double ex=qx-cx,ey=qy-cy,ez=qz-cz;
                     const double roundDistance=DeterministicSqrt(
                         ex*ex+ey*ey+ez*ez)-radius;
+                    const double floorCenterDistanceSq=ex*ex+ey*ey+ez*ez;
                     const double floorT=segment.horizontalLengthSq>1.0e-12
                         ?std::clamp(((qx-segment.a[0])*segment.delta[0]
                             +(qy-segment.a[1])*segment.delta[1])
@@ -1300,24 +1307,43 @@ public:
                         constants,segmentIndex,floorT,segment,qx,qy,floorDepth,qPerMetre);
                     const double flatDistance=PassageFlatBottomDistance(
                         static_cast<float>(roundDistance),floorCenterZ,qz,floorDepth,qPerMetre);
-                    if(flatDistance<bestDistance
-                        ||(flatDistance==bestDistance
+                    // Radius-based tube selection can favor a wider downhill segment
+                    // and carry its lower floor plane backward. Select the floor profile
+                    // by the centerline position, independently of tube radius.
+                    if(floorCenterDistanceSq<bestFloorCenterDistanceSq
+                        ||(floorCenterDistanceSq==bestFloorCenterDistanceSq
+                            &&segmentIndex<nearest.floorSegmentIndex))
+                    {
+                        bestFloorCenterDistanceSq=floorCenterDistanceSq;
+                        nearest.floorCenterZ=floorCenterZ;
+                        nearest.floorDepth=floorDepth;
+                        nearest.floorSegmentIndex=segmentIndex;
+                        nearest.floorT=floorT;
+                    }
+                    // Select the tube segment before applying its floor plane. Taking the
+                    // minimum of each segment's flattened distance lets a lower, downhill
+                    // floor plane extend backward through the overlapping tube and makes
+                    // the floor jump at the prepared-segment spacing.
+                    if(roundDistance<bestDistance
+                        ||(roundDistance==bestDistance
                             &&(!nearest.valid||segmentIndex<nearest.segmentIndex)))
                     {
-                        bestDistance=flatDistance;
+                        bestDistance=roundDistance;
                         nearest.signedDistance=flatDistance;
                         nearest.roundSignedDistance=roundDistance;
                         nearest.segmentIndex=segmentIndex;
                         nearest.t=t;
                         nearest.centerZ=cz;
-                        nearest.floorCenterZ=floorCenterZ;
                         nearest.radius=radius;
-                        nearest.floorDepth=floorDepth;
                         nearest.valid=true;
                     }
                 };
                 VisitNearestPassageSegmentRange(passageIndex,0,lastIndex-1,
-                    qx,qy,qz,0,bestDistance,visitSegment);
+                    qx,qy,qz,0,bestDistance,bestFloorCenterDistanceSq,visitSegment);
+                if(nearest.valid)
+                    nearest.signedDistance=PassageFlatBottomDistance(
+                        static_cast<float>(nearest.roundSignedDistance),
+                        nearest.floorCenterZ,qz,nearest.floorDepth,qPerMetre);
 
                 // Shells form a union over nearby route segments, even when another
                 // segment supplies the nearest interior distance. The hierarchy bound
@@ -1388,8 +1414,10 @@ public:
                     nearest.shellSignedDistance=std::min(nearest.shellSignedDistance,
                         localShellDistance);
                 };
+                double shellFloorSearchBoundSq=-1.0;
                 VisitNearestPassageSegmentRange(passageIndex,0,lastIndex-1,
-                    qx,qy,qz,0,shellSearchBound,visitShellSegment);
+                    qx,qy,qz,0,shellSearchBound,shellFloorSearchBoundSq,
+                    visitShellSegment);
             }
             if(!nearest.valid)continue;
             const double wallElevationMetres=(qz-(nearest.floorCenterZ
@@ -1420,6 +1448,7 @@ public:
                 static_cast<float>(roughRoundDistance),nearest.floorCenterZ,qz,
                 nearest.floorDepth,qPerMetre);
             const auto& segment=PassageSegmentData[passageIndex][nearest.segmentIndex];
+            const auto& floorSegment=PassageSegmentData[passageIndex][nearest.floorSegmentIndex];
             const double alongMetres=segment.authoredAlongMetres
                 +nearest.t*segment.authoredLengthMetres;
             const double mouthDistanceMetres=std::max(0.0,std::min(alongMetres,
@@ -1437,9 +1466,11 @@ public:
             const double mouthWallThickness=segment.routeSegment
                 ?smoothShellFade*shellThickness:0.0;
             double floorExtensionFade=1.0;
-            if(!segment.routeSegment)
+            if(!floorSegment.routeSegment)
             {
-                const double pastMouthMetres=std::max(0.0,alongMetres
+                const double floorAlongMetres=floorSegment.authoredAlongMetres
+                    +nearest.floorT*floorSegment.authoredLengthMetres;
+                const double pastMouthMetres=std::max(0.0,floorAlongMetres
                     -constants.totalPathLengthMetres);
                 const double extensionFade=std::clamp(1.0
                     -pastMouthMetres/MouthShellBlendMetres,0.0,1.0);
@@ -1461,31 +1492,22 @@ public:
         }
 
         if(!std::isfinite(unionDistance))return density;
-        // The union's interior is unconditional air. Its one exterior shell is
-        // solid only in air, so it leaves host rock unchanged. Taking the union
-        // before writing either polarity makes every tunnel interior beat every
-        // overlapping tunnel shell.
-        // Preserve both native graph air and passage interior before any shell
-        // can change their sign. If they overlap, their positive air fields combine.
+        const float passageAirDistance=static_cast<float>(-unionDistance/Q);
+        // Air is the union of the native graph and passage voids. Keeping the
+        // signed passage distance outside the void as well gives marching cubes
+        // a real negative distance through the floor instead of the terrain's
+        // saturated deep-rock value.
         if(nativeTunnelFieldDensity>=0.0f)
-        {
-            const float passageAir=unionDistance<=0.0
-                ?static_cast<float>(-unionDistance/Q)
-                :std::numeric_limits<float>::lowest();
-            return std::max(nativeTunnelFieldDensity,passageAir);
-        }
+            return std::max(nativeTunnelFieldDensity,passageAirDistance);
         if(nativeFloorSupport!=std::numeric_limits<float>::lowest()
             &&nativeFloorSupport<0.0f)
             return std::min(nativeFloorSupport,unionDistance<=0.0
-                ?static_cast<float>(-unionDistance/Q):density);
+                ?passageAirDistance:density);
         if(nativeTunnelFieldDensity!=std::numeric_limits<float>::lowest())
-            return unionDistance<=0.0
-                ?static_cast<float>(-unionDistance/Q):density;
-        if(unionDistance<=0.0)
-            return static_cast<float>(-unionDistance/Q);
-        if(unionShellDistance<0.0&&density>=0.0f)
+            return std::max(density,passageAirDistance);
+        if(unionDistance>0.0&&unionShellDistance<0.0&&density>=0.0f)
             return static_cast<float>(unionShellDistance/Q);
-        return density;
+        return std::max(density,passageAirDistance);
     }
 
     float ApplyResolvedStrateComposition(float density,float X,float Y,float Z) const
@@ -4303,7 +4325,8 @@ private:
     template<class FVisitor>
     void VisitNearestPassageSegmentRange(std::size_t passageIndex,
         std::ptrdiff_t first,std::ptrdiff_t last,double qx,double qy,double qz,
-        int priority,double& bestDistance,FVisitor&& visitor) const
+        int priority,double& bestDistance,double& bestCenterDistanceSq,
+        FVisitor&& visitor) const
     {
         (void)priority;
         if(first>last||passageIndex>=PassageNearestNodes.size()
@@ -4322,13 +4345,22 @@ private:
             return DeterministicSqrt(dx*dx+dy*dy+dz*dz)-node.maximumRadius
                 -SmoothDistanceSlackMetres*qPerMetre;
         };
+        const auto centerDistanceLowerBoundSq=[&](const FPassageNearestNode& node)
+        {
+            const double dx=std::max({node.minimum[0]-qx,0.0,qx-node.maximum[0]});
+            const double dy=std::max({node.minimum[1]-qy,0.0,qy-node.maximum[1]});
+            const double dz=std::max({node.minimum[2]-qz,0.0,qz-node.maximum[2]});
+            return dx*dx+dy*dy+dz*dz;
+        };
         const auto visit=[&](auto&& self,int nodeIndex)->void
         {
             if(nodeIndex<0)return;
             const auto& node=nodes[static_cast<std::size_t>(nodeIndex)];
             if(static_cast<std::ptrdiff_t>(node.maximumSegment)<first
                 ||static_cast<std::ptrdiff_t>(node.minimumSegment)>last
-                ||lowerBound(node)>bestDistance)return;
+                ||(lowerBound(node)>bestDistance
+                    &&(bestCenterDistanceSq<0.0
+                        ||centerDistanceLowerBoundSq(node)>bestCenterDistanceSq)))return;
             if(node.left<0)
             {
                 for(const std::size_t segment:node.segments)
@@ -11430,6 +11462,7 @@ inline void FStandaloneShapeWorld::FScopedPassageTileQueries::prepareSweptTubeBa
                 const double ex=qx-cx,ey=qy-cy,ez=qz-cz;
                 const double signedDistance=FStandaloneShapeWorld::DeterministicSqrt(
                     ex*ex+ey*ey+ez*ez)-radius;
+                const double floorCenterDistanceSq=ex*ex+ey*ey+ez*ez;
                 const double floorT=segment.horizontalLengthSq>1.0e-12
                     ?std::clamp(projectionXY/segment.horizontalLengthSq,0.0,1.0):t;
                 const double floorRadius=segment.radiusA+floorT*segment.radiusDelta;
@@ -11450,6 +11483,17 @@ inline void FStandaloneShapeWorld::FScopedPassageTileQueries::prepareSweptTubeBa
                     *static_cast<std::size_t>(sweep->dimension)+static_cast<std::size_t>(gy))
                     *static_cast<std::size_t>(sweep->dimension)+static_cast<std::size_t>(gx);
                 auto& sample=passageSamples.samples[sampleIndex];
+                if(floorCenterDistanceSq<sample.floorCenterDistanceSq
+                    ||(floorCenterDistanceSq==sample.floorCenterDistanceSq
+                        &&candidate.segmentIndex<sample.floorSegmentIndex))
+                {
+                    sample.floorCenterDistanceSq=floorCenterDistanceSq;
+                    sample.floorCenterZSubvoxels=floorCenterZ;
+                    sample.floorDepthSubvoxels=floorDepth;
+                    sample.floorT=floorT;
+                    sample.floorSegmentIndex=static_cast<std::uint32_t>(
+                        candidate.segmentIndex);
+                }
                 const double alongMetres=segment.authoredAlongMetres
                     +t*segment.authoredLengthMetres;
                 const double mouthDistanceMetres=std::max(0.0,std::min(alongMetres,
@@ -11488,16 +11532,16 @@ inline void FStandaloneShapeWorld::FScopedPassageTileQueries::prepareSweptTubeBa
                     floorShellDistance);
                 sample.shellSignedDistance=std::min(sample.shellSignedDistance,
                     localShellDistance);
-                if(!sample.valid||flatDistance<sample.signedDistance
-                    ||(flatDistance==sample.signedDistance
+                // Rank the tube body by round SDF. Its floor plane is selected
+                // independently above from the nearest centerline position.
+                if(!sample.valid||signedDistance<sample.roundSignedDistance
+                    ||(signedDistance==sample.roundSignedDistance
                         &&candidate.segmentIndex<sample.segmentIndex))
                 {
                     sample.signedDistance=flatDistance;
                     sample.roundSignedDistance=signedDistance;
                     sample.centerZSubvoxels=cz;
-                    sample.floorCenterZSubvoxels=floorCenterZ;
                     sample.radiusSubvoxels=radius;
-                    sample.floorDepthSubvoxels=floorDepth;
                     sample.t=t;
                     sample.segmentIndex=static_cast<std::uint32_t>(candidate.segmentIndex);
                     sample.valid=true;
@@ -11532,6 +11576,9 @@ inline void FStandaloneShapeWorld::FScopedPassageTileQueries::prepareSweptTubeBa
                 +static_cast<std::int64_t>(gy)*sweep->stepSubvoxels);
             const double qz=static_cast<double>(sweep->gridMinimumSubvoxels[2]
                 +static_cast<std::int64_t>(gz)*sweep->stepSubvoxels);
+            sample.signedDistance=FStandaloneShapeWorld::PassageFlatBottomDistance(
+                static_cast<float>(sample.roundSignedDistance),
+                sample.floorCenterZSubvoxels,qz,sample.floorDepthSubvoxels,qPerMetre);
             const double radius=sample.radiusSubvoxels;
             const double centerZ=sample.centerZSubvoxels;
             if(sample.signedDistance<=sweep->influenceSubvoxels)