diff --git a/source/build/include/build.h b/source/build/include/build.h
index 47a6a90db..6e469c60f 100644
--- a/source/build/include/build.h
+++ b/source/build/include/build.h
@@ -606,7 +606,6 @@ static FORCE_INLINE int32_t E_SpriteIsValid(const int32_t i)
 
 void   alignceilslope(int16_t dasect, int32_t x, int32_t y, int32_t z);
 void   alignflorslope(int16_t dasect, int32_t x, int32_t y, int32_t z);
-int32_t sectorofwall(int16_t wallNum);
 void setslope(int32_t sectnum, int32_t cf, int16_t slope);
 
 int32_t lintersect(int32_t originX, int32_t originY, int32_t originZ,
diff --git a/source/build/include/buildtypes.h b/source/build/include/buildtypes.h
index 757627400..ac0cf6f3e 100644
--- a/source/build/include/buildtypes.h
+++ b/source/build/include/buildtypes.h
@@ -51,6 +51,7 @@ struct sectortype
     int16_t hitag;
     int16_t extra;
 
+    uint8_t dirty;
     float ceilingxpan_, ceilingypan_, floorxpan_, floorypan_;
 
     int ceilingxpan() const { return int(ceilingxpan_); }
@@ -91,7 +92,7 @@ struct walltype
         };
         vec2_t pos;
     };
-    int16_t point2, nextwall, nextsector;
+    int16_t point2, nextwall, sector, nextsector;
     uint16_t cstat;
     int16_t picnum, overpicnum;
     int8_t shade;
diff --git a/source/build/src/engine.cpp b/source/build/src/engine.cpp
index 6c8a52cba..c873e3124 100644
--- a/source/build/src/engine.cpp
+++ b/source/build/src/engine.cpp
@@ -2323,6 +2323,7 @@ void dragpoint(int16_t pointhighlight, int32_t dax, int32_t day, uint8_t flags)
 
         while (1)
         {
+            sector[wall[w].sector].dirty = 255;
             wall[w].x = dax;
             wall[w].y = day;
             walbitmap[w>>3] |= pow2char[w&7];
@@ -2839,36 +2840,6 @@ void renderCompleteMirror(void)
 }
 
 
-//
-// sectorofwall
-//
-static int32_t sectorofwall_internal(int16_t wallNum)
-{
-    native_t gap = numsectors>>1, sectNum = gap;
-
-    while (gap > 1)
-    {
-        gap >>= 1;
-        native_t const n = !!(sector[sectNum].wallptr < wallNum);
-        sectNum += (n ^ (n - 1)) * gap;
-    }
-    while (sector[sectNum].wallptr > wallNum) sectNum--;
-    while (sector[sectNum].wallptr + sector[sectNum].wallnum <= wallNum) sectNum++;
-
-    return sectNum;
-}
-
-int32_t sectorofwall(int16_t wallNum)
-{
-	if ((unsigned)wallNum < (unsigned)numwalls)
-	{
-		native_t const w = wall[wallNum].nextwall;
-		return ((unsigned)w < MAXWALLS) ? wall[w].nextsector : sectorofwall_internal(wallNum);
-	}
-	return -1;
-}
-
-
 int32_t getceilzofslopeptr(usectorptr_t sec, int32_t dax, int32_t day)
 {
     if (!(sec->ceilingstat&2))
diff --git a/source/core/gamefuncs.cpp b/source/core/gamefuncs.cpp
index 92b8f534e..fbc6a8bcd 100644
--- a/source/core/gamefuncs.cpp
+++ b/source/core/gamefuncs.cpp
@@ -175,7 +175,7 @@ bool spriteIsModelOrVoxel(const spritetype * tspr)
 //
 //==========================================================================
 
-void PlanesAtPoint(usectorptr_t sec, float dax, float day, float* pceilz, float* pflorz)
+void PlanesAtPoint(const sectortype* sec, float dax, float day, float* pceilz, float* pflorz)
 {
 	float ceilz = float(sec->ceilingz);
 	float florz = float(sec->floorz);
@@ -200,25 +200,3 @@ void PlanesAtPoint(usectorptr_t sec, float dax, float day, float* pceilz, float*
 	if (pceilz) *pceilz = ceilz * -(1.f / 256.f);
 	if (pflorz) *pflorz = florz * -(1.f / 256.f);
 }
-
-// variant that allows to pass precalculated info for the first line in. For cases where multiple points in a sector need to be checked.
-void PlanesAtPoint(usectorptr_t sec, PlaneParam *pp, float dax, float day, float* pceilz, float* pflorz)
-{
-	float ceilz = float(sec->ceilingz);
-	float florz = float(sec->floorz);
-
-	if (((sec->ceilingstat | sec->floorstat) & CSTAT_SECTOR_SLOPE) == CSTAT_SECTOR_SLOPE)
-	{
-		if (pp->length != 0)
-		{
-			auto wal = &wall[sec->wallptr];
-			float const j = (pp->dx * (day - wal->y) - pp->dy * (dax - wal->x)) * (1.f / 8.f);
-			if (sec->ceilingstat & CSTAT_SECTOR_SLOPE) ceilz += (sec->ceilingheinum * j) / pp->length;
-			if (sec->floorstat & CSTAT_SECTOR_SLOPE) florz += (sec->floorheinum * j) / pp->length;
-		}
-	}
-	// Scale to render coordinates.
-	if (pceilz) *pceilz = ceilz * -(1.f / 256.f);
-	if (pflorz) *pflorz = florz * -(1.f / 256.f);
-}
-
diff --git a/source/core/gamefuncs.h b/source/core/gamefuncs.h
index f7ca8e8de..67955e795 100644
--- a/source/core/gamefuncs.h
+++ b/source/core/gamefuncs.h
@@ -8,15 +8,8 @@ extern int cameradist, cameraclock;
 
 bool calcChaseCamPos(int* px, int* py, int* pz, spritetype* pspr, short *psectnum, binangle ang, fixedhoriz horiz, double const smoothratio);
 bool spriteIsModelOrVoxel(const spritetype* tspr);
-void PlanesAtPoint(usectorptr_t sec, float dax, float day, float* ceilz, float* florz);
-
-struct PlaneParam
-{
-    float dx, dy;
-    int length;
-};
-
-void PlanesAtPoint(usectorptr_t sec, PlaneParam* pp, float dax, float day, float* ceilz, float* florz);
+void PlanesAtPoint(const sectortype* sec, float dax, float day, float* ceilz, float* florz);
+void setWallSectors();
 
 // y is negated so that the orientation is the same as in GZDoom, in order to use its utilities.
 // The render code should NOT use Build coordinates for anything!
@@ -76,3 +69,10 @@ inline double PointOnLineSide(double x, double y, double linex, double liney, do
     return (x - linex) * deltay - (y - liney) * deltax;
 }
 
+inline int sectorofwall(int wallNum)
+{
+    if ((unsigned)wallNum < (unsigned)numwalls) return wall[wallNum].sector;
+    return -1;
+}
+
+
diff --git a/source/core/interpolate.cpp b/source/core/interpolate.cpp
index 8ccab4f41..8601b25b7 100644
--- a/source/core/interpolate.cpp
+++ b/source/core/interpolate.cpp
@@ -72,8 +72,8 @@ void Set(int index, int type, double val)
 	case Interp_Sect_CeilingPanX:       sector[index].ceilingxpan_ = float(val); break;
 	case Interp_Sect_CeilingPanY:       sector[index].ceilingypan_ = float(val); break;
                                         
-	case Interp_Wall_X:                 wall[index].x = xs_CRoundToInt(val); break;
-	case Interp_Wall_Y:                 wall[index].y = xs_CRoundToInt(val); break;
+	case Interp_Wall_X:                 wall[index].x = xs_CRoundToInt(val); sector[wall[index].sector].dirty = 255; break;
+	case Interp_Wall_Y:                 wall[index].y = xs_CRoundToInt(val); sector[wall[index].sector].dirty = 255; break;
 	case Interp_Wall_PanX:              wall[index].xpan_ = float(val);  break;
 	case Interp_Wall_PanY:              wall[index].ypan_ = float(val);  break;
                                         
diff --git a/source/core/maploader.cpp b/source/core/maploader.cpp
index b2c887ac6..e38ff0584 100644
--- a/source/core/maploader.cpp
+++ b/source/core/maploader.cpp
@@ -41,6 +41,7 @@
 #include "inputstate.h"
 #include "md4.h"
 #include "gamecontrol.h"
+#include "gamefuncs.h"
 
 
 static void ReadSectorV7(FileReader& fr, sectortype& sect)
@@ -444,6 +445,7 @@ void engineLoadBoard(const char* filename, int flags, vec3_t* pos, int16_t* ang,
 	unsigned char md4[16];
 	md4once(buffer.Data(), buffer.Size(), md4);
 	G_LoadMapHack(filename, md4);
+	setWallSectors();
 
 	memcpy(wallbackup, wall, sizeof(wallbackup));
 	memcpy(sectorbackup, sector, sizeof(sectorbackup));
@@ -468,4 +470,17 @@ void loadMapBackup(const char* filename)
 		engineLoadBoard(filename, 0, &pos, &scratch, &scratch);
 		initspritelists();
 	}
+}
+
+// Sets the sector reference for each wall. We need this for the triangulation cache.
+void setWallSectors()
+{
+	for (int i = 0; i < numsectors; i++)
+	{
+		sector[i].dirty = 255;
+		for (int w = 0; w < sector[i].wallnum; w++)
+		{
+			wall[sector[i].wallptr + w].sector = i;
+		}
+	}
 }
\ No newline at end of file
diff --git a/source/core/savegamehelp.cpp b/source/core/savegamehelp.cpp
index 32440c6dc..3e9faf194 100644
--- a/source/core/savegamehelp.cpp
+++ b/source/core/savegamehelp.cpp
@@ -56,6 +56,7 @@
 #include "gamestate.h"
 #include "razemenu.h"
 #include "interpolate.h"
+#include "gamefuncs.h"
 
 
 sectortype sectorbackup[MAXSECTORS];
@@ -670,6 +671,10 @@ void SerializeMap(FSerializer& arc)
 		if (prevspritestat[i] == -2) prevspritestat[i] = i - 1;
 		if (prevspritesect[i] == -2) prevspritesect[i] = i - 1;
 	}
+	if (arc.isReading())
+	{
+		setWallSectors();
+	}
 }
 
 //=============================================================================
diff --git a/source/games/blood/src/db.cpp b/source/games/blood/src/db.cpp
index 1baf4f7ff..5df48a6fc 100644
--- a/source/games/blood/src/db.cpp
+++ b/source/games/blood/src/db.cpp
@@ -31,6 +31,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include "md4.h"
 #include "automap.h"
 #include "raze_sound.h"
+#include "gamefuncs.h"
 
 #include "blood.h"
 
@@ -1058,6 +1059,7 @@ void dbLoadMap(const char *pPath, int *pX, int *pY, int *pZ, short *pAngle, shor
         }
     }
 
+    setWallSectors();
     memcpy(wallbackup, wall, sizeof(wallbackup));
     memcpy(sectorbackup, sector, sizeof(sectorbackup));
 }
diff --git a/source/games/blood/src/triggers.cpp b/source/games/blood/src/triggers.cpp
index 4bbaf9c7f..5320726f6 100644
--- a/source/games/blood/src/triggers.cpp
+++ b/source/games/blood/src/triggers.cpp
@@ -794,6 +794,7 @@ void PathSound(int nSector, int nSound)
 
 void DragPoint(int nWall, int x, int y)
 {
+    sector[wall[nWall].sector].dirty = 255; 
     viewInterpolateWall(nWall, &wall[nWall]);
     wall[nWall].x = x;
     wall[nWall].y = y;
@@ -805,6 +806,7 @@ void DragPoint(int nWall, int x, int y)
         if (wall[vb].nextwall >= 0)
         {
             vb = wall[wall[vb].nextwall].point2;
+            sector[wall[vb].sector].dirty = 255;
             viewInterpolateWall(vb, &wall[vb]);
             wall[vb].x = x;
             wall[vb].y = y;
@@ -817,6 +819,7 @@ void DragPoint(int nWall, int x, int y)
                 if (wall[lastwall(vb)].nextwall >= 0)
                 {
                     vb = wall[lastwall(vb)].nextwall;
+                    sector[wall[vb].sector].dirty = 255;
                     viewInterpolateWall(vb, &wall[vb]);
                     wall[vb].x = x;
                     wall[vb].y = y;