diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e57a9b412a..db6d9db160 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -23,6 +23,7 @@ add_subdirectory(saveload)
 add_subdirectory(sound)
 add_subdirectory(spriteloader)
 add_subdirectory(table)
+add_subdirectory(tests)
 add_subdirectory(video)
 add_subdirectory(widgets)
 
diff --git a/src/clear_cmd.cpp b/src/clear_cmd.cpp
index 1032fe09f6..2035b9d5d5 100644
--- a/src/clear_cmd.cpp
+++ b/src/clear_cmd.cpp
@@ -197,7 +197,7 @@ static void DrawTile_Clear(TileInfo *ti, DrawTileProcParams params)
 	DrawBridgeMiddle(ti);
 }
 
-static int GetSlopePixelZ_Clear(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Clear(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	int z;
 	Slope tileh = GetTilePixelSlope(tile, &z);
diff --git a/src/core/bitmath_func.hpp b/src/core/bitmath_func.hpp
index b931205ccd..e082a89bab 100644
--- a/src/core/bitmath_func.hpp
+++ b/src/core/bitmath_func.hpp
@@ -31,7 +31,7 @@
  * @return The selected bits, aligned to a LSB.
  */
 template <typename T>
-debug_inline static uint GB(const T x, const uint8 s, const uint8 n)
+debug_inline constexpr static uint GB(const T x, const uint8 s, const uint8 n)
 {
 	return (x >> s) & (((T)1U << n) - 1);
 }
diff --git a/src/core/math_func.hpp b/src/core/math_func.hpp
index 7d5bfa008b..ea0345ce5c 100644
--- a/src/core/math_func.hpp
+++ b/src/core/math_func.hpp
@@ -224,7 +224,7 @@ static inline bool IsInsideBS(const T x, const size_t base, const size_t size)
  * @see IsInsideBS()
  */
 template <typename T>
-static inline bool IsInsideMM(const T x, const size_t min, const size_t max)
+static inline constexpr bool IsInsideMM(const T x, const size_t min, const size_t max)
 {
 	return (size_t)(x - min) < (max - min);
 }
diff --git a/src/elrail.cpp b/src/elrail.cpp
index e079fb30b4..de661fdb4f 100644
--- a/src/elrail.cpp
+++ b/src/elrail.cpp
@@ -266,7 +266,7 @@ static int GetPCPElevation(TileIndex tile, DiagDirection PCPpos)
 	 */
 
 	int z = GetSlopePixelZ(TileX(tile) * TILE_SIZE + std::min<int8>(x_pcp_offsets[PCPpos], TILE_SIZE - 1),
-	                       TileY(tile) * TILE_SIZE + std::min<int8>(y_pcp_offsets[PCPpos], TILE_SIZE - 1));
+	                       TileY(tile) * TILE_SIZE + std::min<int8>(y_pcp_offsets[PCPpos], TILE_SIZE - 1), true);
 	return (z + 2) & ~3; // this means z = (z + TILE_HEIGHT / 4) / (TILE_HEIGHT / 2) * (TILE_HEIGHT / 2);
 }
 
@@ -591,7 +591,7 @@ static void DrawRailCatenaryRailway(const TileInfo *ti)
 		 * down to the nearest full height change.
 		 */
 		AddSortableSpriteToDraw(wire_base + sss->image_offset, PAL_NONE, ti->x + sss->x_offset, ti->y + sss->y_offset,
-			sss->x_size, sss->y_size, sss->z_size, (GetSlopePixelZ(ti->x + sss->x_offset, ti->y + sss->y_offset) + 4) / 8 * 8 + sss->z_offset,
+			sss->x_size, sss->y_size, sss->z_size, (GetSlopePixelZ(ti->x + sss->x_offset, ti->y + sss->y_offset, true) + 4) / 8 * 8 + sss->z_offset,
 			IsTransparencySet(TO_CATENARY));
 	}
 }
diff --git a/src/ground_vehicle.hpp b/src/ground_vehicle.hpp
index 48b86b3625..87e51e25b5 100644
--- a/src/ground_vehicle.hpp
+++ b/src/ground_vehicle.hpp
@@ -151,7 +151,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 	 */
 	inline void UpdateZPositionAndInclination()
 	{
-		this->z_pos = GetSlopePixelZ(this->x_pos, this->y_pos);
+		this->z_pos = GetSlopePixelZ(this->x_pos, this->y_pos, true);
 		ClrBit(this->gv_flags, GVF_GOINGUP_BIT);
 		ClrBit(this->gv_flags, GVF_GOINGDOWN_BIT);
 
@@ -160,7 +160,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 			 * direction it is sloped, we get the 'z' at the center of
 			 * the tile (middle_z) and the edge of the tile (old_z),
 			 * which we then can compare. */
-			int middle_z = GetSlopePixelZ((this->x_pos & ~TILE_UNIT_MASK) | (TILE_SIZE / 2), (this->y_pos & ~TILE_UNIT_MASK) | (TILE_SIZE / 2));
+			int middle_z = GetSlopePixelZ((this->x_pos & ~TILE_UNIT_MASK) | (TILE_SIZE / 2), (this->y_pos & ~TILE_UNIT_MASK) | (TILE_SIZE / 2), true);
 
 			if (middle_z != this->z_pos) {
 				SetBit(this->gv_flags, (middle_z > this->z_pos) ? GVF_GOINGUP_BIT : GVF_GOINGDOWN_BIT);
@@ -183,25 +183,25 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 		if (HasBit(this->gv_flags, GVF_GOINGUP_BIT)) {
 			switch (this->direction) {
 				case DIR_NE:
-					this->z_pos += (this->x_pos & 1); break;
-				case DIR_SW:
 					this->z_pos += (this->x_pos & 1) ^ 1; break;
+				case DIR_SW:
+					this->z_pos += (this->x_pos & 1); break;
 				case DIR_NW:
-					this->z_pos += (this->y_pos & 1); break;
-				case DIR_SE:
 					this->z_pos += (this->y_pos & 1) ^ 1; break;
+				case DIR_SE:
+					this->z_pos += (this->y_pos & 1); break;
 				default: break;
 			}
 		} else if (HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
 			switch (this->direction) {
 				case DIR_NE:
-					this->z_pos -= (this->x_pos & 1); break;
-				case DIR_SW:
 					this->z_pos -= (this->x_pos & 1) ^ 1; break;
+				case DIR_SW:
+					this->z_pos -= (this->x_pos & 1); break;
 				case DIR_NW:
-					this->z_pos -= (this->y_pos & 1); break;
-				case DIR_SE:
 					this->z_pos -= (this->y_pos & 1) ^ 1; break;
+				case DIR_SE:
+					this->z_pos -= (this->y_pos & 1); break;
 				default: break;
 			}
 		}
@@ -218,7 +218,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 		if (HasBit(this->gv_flags, GVF_GOINGUP_BIT) || HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
 			if (T::From(this)->HasToUseGetSlopePixelZ()) {
 				/* In some cases, we have to use GetSlopePixelZ() */
-				this->z_pos = GetSlopePixelZ(this->x_pos, this->y_pos);
+				this->z_pos = GetSlopePixelZ(this->x_pos, this->y_pos, true);
 				return;
 			}
 			/* DirToDiagDir() is a simple right shift */
@@ -230,8 +230,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 			int8 d = DiagDirToAxis(dir) == AXIS_X ? x_pos : y_pos;
 			/* We need only the least significant bit */
 			d &= 1;
-			/* Conditional "^ 1". Optimised to "(dir - 1) <= 1". */
-			d ^= (int8)(dir == DIAGDIR_SW || dir == DIAGDIR_SE);
+			d ^= (int8)(dir == DIAGDIR_NW || dir == DIAGDIR_NE);
 			/* Subtraction instead of addition because we are testing for GVF_GOINGUP_BIT.
 			 * GVF_GOINGUP_BIT is used because it's bit 0, so simple AND can be used,
 			 * without any shift */
@@ -239,7 +238,7 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 		}
 
 #ifdef _DEBUG
-		assert(this->z_pos == GetSlopePixelZ(this->x_pos, this->y_pos));
+		assert(this->z_pos == GetSlopePixelZ(this->x_pos, this->y_pos, true));
 #endif
 
 		if (HasBit(this->gv_flags, GVF_CHUNNEL_BIT) && !IsTunnelTile(this->tile)) {
diff --git a/src/industry_cmd.cpp b/src/industry_cmd.cpp
index 94ea2bf9b3..0adf0801b4 100644
--- a/src/industry_cmd.cpp
+++ b/src/industry_cmd.cpp
@@ -387,7 +387,7 @@ static void DrawTile_Industry(TileInfo *ti, DrawTileProcParams params)
 	}
 }
 
-static int GetSlopePixelZ_Industry(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Industry(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	return GetTileMaxPixelZ(tile);
 }
diff --git a/src/landscape.cpp b/src/landscape.cpp
index 5381006de2..56ec9b25e7 100644
--- a/src/landscape.cpp
+++ b/src/landscape.cpp
@@ -226,144 +226,112 @@ uint ApplyFoundationToSlope(Foundation f, Slope *s)
 
 
 /**
- * Determines height at given coordinate of a slope
- * @param x x coordinate
- * @param y y coordinate
+ * Determines height at given coordinate of a slope.
+ *
+ * At the northern corner (0, 0) the result is always a multiple of TILE_HEIGHT.
+ * When the height is a fractional Z, then the height is rounded down. For example,
+ * when at the height is 0 at x = 0 and the height is 8 at x = 16 (actually x = 0
+ * of the next tile), then height is 0 at x = 1, 1 at x = 2, and 7 at x = 15.
+ * @param x x coordinate (value from 0 to 15)
+ * @param y y coordinate (value from 0 to 15)
  * @param corners slope to examine
  * @return height of given point of given slope
  */
-uint GetPartialPixelZ(int x, int y, Slope corners)
+static constexpr uint InternalGetPartialPixelZ(int x, int y, Slope corners)
 {
 	if (IsHalftileSlope(corners)) {
+		/* A foundation is placed on half the tile at a specific corner. This means that,
+		 * depending on the corner, that one half of the tile is at the maximum height. */
 		switch (GetHalftileSlopeCorner(corners)) {
 			case CORNER_W:
-				if (x - y >= 0) return GetSlopeMaxPixelZ(corners);
+				if (x > y) return GetSlopeMaxPixelZ(corners);
 				break;
 
 			case CORNER_S:
-				if (x - (y ^ 0xF) >= 0) return GetSlopeMaxPixelZ(corners);
+				if (x + y >= (int)TILE_SIZE) return GetSlopeMaxPixelZ(corners);
 				break;
 
 			case CORNER_E:
-				if (y - x >= 0) return GetSlopeMaxPixelZ(corners);
+				if (x <= y) return GetSlopeMaxPixelZ(corners);
 				break;
 
 			case CORNER_N:
-				if ((y ^ 0xF) - x >= 0) return GetSlopeMaxPixelZ(corners);
+				if (x + y < (int)TILE_SIZE) return GetSlopeMaxPixelZ(corners);
 				break;
 
 			default: NOT_REACHED();
 		}
 	}
 
-	int z = 0;
-
 	switch (RemoveHalftileSlope(corners)) {
-		case SLOPE_W:
-			if (x - y >= 0) {
-				z = (x - y) >> 1;
-			}
-			break;
+		case SLOPE_FLAT: return 0;
 
-		case SLOPE_S:
-			y ^= 0xF;
-			if ((x - y) >= 0) {
-				z = (x - y) >> 1;
-			}
-			break;
+		/* One corner is up.*/
+		case SLOPE_N: return x + y <= (int)TILE_SIZE ? (TILE_SIZE - x - y)     >> 1 : 0;
+		case SLOPE_E: return y >= x                  ? (1 + y - x)             >> 1 : 0;
+		case SLOPE_S: return x + y >= (int)TILE_SIZE ? (1 + x + y - TILE_SIZE) >> 1 : 0;
+		case SLOPE_W: return x >= y                  ? (x - y)                 >> 1 : 0;
 
-		case SLOPE_SW:
-			z = (x >> 1) + 1;
-			break;
+		/* Two corners next to eachother are up. */
+		case SLOPE_NE: return (TILE_SIZE - x) >> 1;
+		case SLOPE_SE: return (y + 1) >> 1;
+		case SLOPE_SW: return (x + 1) >> 1;
+		case SLOPE_NW: return (TILE_SIZE - y) >> 1;
 
-		case SLOPE_E:
-			if (y - x >= 0) {
-				z = (y - x) >> 1;
-			}
-			break;
+		/* Three corners are up on the same level. */
+		case SLOPE_ENW: return x + y >= (int)TILE_SIZE ? TILE_HEIGHT - ((1 + x + y - TILE_SIZE) >> 1) : TILE_HEIGHT;
+		case SLOPE_SEN: return y < x                   ? TILE_HEIGHT - ((x - y)                 >> 1) : TILE_HEIGHT;
+		case SLOPE_WSE: return x + y <= (int)TILE_SIZE ? TILE_HEIGHT - ((TILE_SIZE - x - y)     >> 1) : TILE_HEIGHT;
+		case SLOPE_NWS: return x < y                   ? TILE_HEIGHT - ((1 + y - x)             >> 1) : TILE_HEIGHT;
 
-		case SLOPE_EW:
-		case SLOPE_NS:
-		case SLOPE_ELEVATED:
-			z = 4;
-			break;
+		/* Two corners at opposite sides are up. */
+		case SLOPE_NS: return x + y < (int)TILE_SIZE ? (TILE_SIZE - x - y) >> 1 : (1 + x + y - TILE_SIZE) >> 1;
+		case SLOPE_EW: return x >= y ? (x - y) >> 1 : (1 + y - x) >> 1;
 
-		case SLOPE_SE:
-			z = (y >> 1) + 1;
-			break;
+		/* Very special cases. */
+		case SLOPE_ELEVATED: return TILE_HEIGHT;
 
-		case SLOPE_WSE:
-			z = 8;
-			y ^= 0xF;
-			if (x - y < 0) {
-				z += (x - y) >> 1;
-			}
-			break;
+		/* Steep slopes. The top is at 2 * TILE_HEIGHT. */
+		case SLOPE_STEEP_N: return (TILE_SIZE - x + TILE_SIZE - y) >> 1;
+		case SLOPE_STEEP_E: return (TILE_SIZE + 1 + y - x) >> 1;
+		case SLOPE_STEEP_S: return (1 + x + y) >> 1;
+		case SLOPE_STEEP_W: return (TILE_SIZE + x - y) >> 1;
 
-		case SLOPE_N:
-			y ^= 0xF;
-			if (y - x >= 0) {
-				z = (y - x) >> 1;
-			}
-			break;
-
-		case SLOPE_NW:
-			z = (y ^ 0xF) >> 1;
-			break;
-
-		case SLOPE_NWS:
-			z = 8;
-			if (x - y < 0) {
-				z += (x - y) >> 1;
-			}
-			break;
-
-		case SLOPE_NE:
-			z = (x ^ 0xF) >> 1;
-			break;
-
-		case SLOPE_ENW:
-			z = 8;
-			y ^= 0xF;
-			if (y - x < 0) {
-				z += (y - x) >> 1;
-			}
-			break;
-
-		case SLOPE_SEN:
-			z = 8;
-			if (y - x < 0) {
-				z += (y - x) >> 1;
-			}
-			break;
-
-		case SLOPE_STEEP_S:
-			z = 1 + ((x + y) >> 1);
-			break;
-
-		case SLOPE_STEEP_W:
-			z = 1 + ((x + (y ^ 0xF)) >> 1);
-			break;
-
-		case SLOPE_STEEP_N:
-			z = 1 + (((x ^ 0xF) + (y ^ 0xF)) >> 1);
-			break;
-
-		case SLOPE_STEEP_E:
-			z = 1 + (((x ^ 0xF) + y) >> 1);
-			break;
-
-		default: break;
+		default: NOT_REACHED();
 	}
-
-	return z;
 }
 
-int GetSlopePixelZ(int x, int y)
+#include "tests/landscape_partial_pixel_z.h"
+
+/**
+ * Determines height at given coordinate of a slope.
+ * See #InternalGetPartialPixelZ.
+ * @param x x coordinate (value from 0 to 15)
+ * @param y y coordinate (value from 0 to 15)
+ * @param corners slope to examine
+ * @return height of given point of given slope
+ */
+uint GetPartialPixelZ(int x, int y, Slope corners)
+{
+	return InternalGetPartialPixelZ(x, y, corners);
+}
+
+/**
+ * Return world \c Z coordinate of a given point of a tile. Normally this is the
+ * Z of the ground/foundation at the given location, but in some cases the
+ * ground/foundation can differ from the Z coordinate that the (ground) vehicle
+ * passing over it would take. For example when entering a tunnel or bridge.
+ *
+ * @param x World X coordinate in tile "units".
+ * @param y World Y coordinate in tile "units".
+ * @param ground_vehicle Whether to get the Z coordinate of the ground vehicle, or the ground.
+ * @return World Z coordinate at tile ground (vehicle) level, including slopes and foundations.
+ */
+int GetSlopePixelZ(int x, int y, bool ground_vehicle)
 {
 	TileIndex tile = TileVirtXY(x, y);
 
-	return _tile_type_procs[GetTileType(tile)]->get_slope_z_proc(tile, x, y);
+	return _tile_type_procs[GetTileType(tile)]->get_slope_z_proc(tile, x, y, ground_vehicle);
 }
 
 /**
@@ -377,9 +345,9 @@ int GetSlopePixelZ(int x, int y)
 int GetSlopePixelZOutsideMap(int x, int y)
 {
 	if (IsInsideBS(x, 0, MapSizeX() * TILE_SIZE) && IsInsideBS(y, 0, MapSizeY() * TILE_SIZE)) {
-		return GetSlopePixelZ(x, y);
+		return GetSlopePixelZ(x, y, false);
 	} else {
-		return _tile_type_procs[MP_VOID]->get_slope_z_proc(INVALID_TILE, x, y);
+		return _tile_type_procs[MP_VOID]->get_slope_z_proc(INVALID_TILE, x, y, false);
 	}
 }
 
diff --git a/src/landscape.h b/src/landscape.h
index d0f15586a2..a6f9e14e7f 100644
--- a/src/landscape.h
+++ b/src/landscape.h
@@ -67,7 +67,7 @@ Slope GetFoundationSlopeFromTileSlope(TileIndex tile, Slope tileh, int *z = null
 Slope GetFoundationSlope(TileIndex tile, int *z = nullptr);
 
 uint GetPartialPixelZ(int x, int y, Slope corners);
-int GetSlopePixelZ(int x, int y);
+int GetSlopePixelZ(int x, int y, bool ground_vehicle = false);
 int GetSlopePixelZOutsideMap(int x, int y);
 void GetSlopePixelZOnEdge(Slope tileh, DiagDirection edge, int *z1, int *z2);
 
@@ -127,7 +127,7 @@ static inline Point RemapCoords(int x, int y, int z)
  */
 static inline Point RemapCoords2(int x, int y)
 {
-	return RemapCoords(x, y, GetSlopePixelZ(x, y));
+	return RemapCoords(x, y, GetSlopePixelZ(x, y, false));
 }
 
 /**
diff --git a/src/object_cmd.cpp b/src/object_cmd.cpp
index f0b0eee69d..2ba8a90c15 100644
--- a/src/object_cmd.cpp
+++ b/src/object_cmd.cpp
@@ -659,7 +659,7 @@ static void DrawTile_Object(TileInfo *ti, DrawTileProcParams params)
 	DrawBridgeMiddle(ti);
 }
 
-static int GetSlopePixelZ_Object(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Object(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	if (IsObjectType(tile, OBJECT_OWNED_LAND)) {
 		int z;
diff --git a/src/pathfinder/npf/npf.cpp b/src/pathfinder/npf/npf.cpp
index d4b82b1f09..c261af2d6e 100644
--- a/src/pathfinder/npf/npf.cpp
+++ b/src/pathfinder/npf/npf.cpp
@@ -226,8 +226,8 @@ static uint NPFSlopeCost(AyStarNode *current)
 	/* Get the height on both sides of the tile edge.
 	 * Avoid testing the height on the tile-center. This will fail for halftile-foundations.
 	 */
-	int z1 = GetSlopePixelZ(x1 + dx4, y1 + dy4);
-	int z2 = GetSlopePixelZ(x2 - dx4, y2 - dy4);
+	int z1 = GetSlopePixelZ(x1 + dx4, y1 + dy4, true);
+	int z2 = GetSlopePixelZ(x2 - dx4, y2 - dy4, true);
 
 	if (z2 - z1 > 1) {
 		/* Slope up */
diff --git a/src/pathfinder/yapf/yapf_road.cpp b/src/pathfinder/yapf/yapf_road.cpp
index df33fcbedb..3bc96521e5 100644
--- a/src/pathfinder/yapf/yapf_road.cpp
+++ b/src/pathfinder/yapf/yapf_road.cpp
@@ -53,12 +53,12 @@ protected:
 		/* height of the center of the current tile */
 		int x1 = TileX(tile) * TILE_SIZE;
 		int y1 = TileY(tile) * TILE_SIZE;
-		int z1 = GetSlopePixelZ(x1 + TILE_SIZE / 2, y1 + TILE_SIZE / 2);
+		int z1 = GetSlopePixelZ(x1 + TILE_SIZE / 2, y1 + TILE_SIZE / 2, true);
 
 		/* height of the center of the next tile */
 		int x2 = TileX(next_tile) * TILE_SIZE;
 		int y2 = TileY(next_tile) * TILE_SIZE;
-		int z2 = GetSlopePixelZ(x2 + TILE_SIZE / 2, y2 + TILE_SIZE / 2);
+		int z2 = GetSlopePixelZ(x2 + TILE_SIZE / 2, y2 + TILE_SIZE / 2, true);
 
 		if (z2 - z1 > 1) {
 			/* Slope up */
diff --git a/src/pbs.cpp b/src/pbs.cpp
index 3c0a034d49..dea262268e 100644
--- a/src/pbs.cpp
+++ b/src/pbs.cpp
@@ -439,7 +439,7 @@ static PBSTileInfo FollowReservation(Owner o, RailTypes rts, TileIndex tile, Tra
 						default: NOT_REACHED();
 					}
 				}
-				z = GetSlopePixelZ(x, y);
+				z = GetSlopePixelZ(x, y, true);
 			}
 		}
 	};
diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index 9d68908f78..32b732e7ee 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -3752,7 +3752,7 @@ void DrawTrainDepotSprite(int x, int y, int dir, RailType railtype)
 	DrawRailTileSeqInGUI(x, y, dts, offset, 0, palette);
 }
 
-static int GetSlopePixelZ_Track(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Track(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	if (IsPlainRail(tile)) {
 		int z;
diff --git a/src/road_cmd.cpp b/src/road_cmd.cpp
index 8a7e45acf0..95022fbee7 100644
--- a/src/road_cmd.cpp
+++ b/src/road_cmd.cpp
@@ -2494,7 +2494,7 @@ void UpdateNearestTownForRoadTiles(bool invalidate)
 	}
 }
 
-static int GetSlopePixelZ_Road(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Road(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 
 	if (IsNormalRoad(tile)) {
diff --git a/src/roadveh_cmd.cpp b/src/roadveh_cmd.cpp
index 1cc528b6bc..bf46c8929d 100644
--- a/src/roadveh_cmd.cpp
+++ b/src/roadveh_cmd.cpp
@@ -288,7 +288,7 @@ CommandCost CmdBuildRoadVehicle(TileIndex tile, DoCommandFlag flags, const Engin
 		int y = TileY(tile) * TILE_SIZE + TILE_SIZE / 2;
 		v->x_pos = x;
 		v->y_pos = y;
-		v->z_pos = GetSlopePixelZ(x, y);
+		v->z_pos = GetSlopePixelZ(x, y, true);
 
 		v->state = RVSB_IN_DEPOT;
 		v->vehstatus = VS_HIDDEN | VS_STOPPED | VS_DEFPAL;
@@ -2013,7 +2013,7 @@ again:
 		 * A vehicle has to spend at least 9 frames on a tile, so the following articulated part can follow.
 		 * (The following part may only be one tile behind, and the front part is moved before the following ones.)
 		 * The short (inner) curve has 8 frames, this elongates it to 10. */
-		v->UpdateInclination(false, true);
+		v->UpdateViewport(true, true);
 		return true;
 	}
 
diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
index 964106b5ec..cf750cd6ab 100644
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -569,12 +569,12 @@ static uint FixVehicleInclination(Vehicle *v, Direction dir)
 		case INVALID_DIR: break;
 		default: NOT_REACHED();
 	}
-	byte entry_z = GetSlopePixelZ(entry_x, entry_y);
+	byte entry_z = GetSlopePixelZ(entry_x, entry_y, true);
 
 	/* Compute middle of the tile. */
 	int middle_x = (v->x_pos & ~TILE_UNIT_MASK) + TILE_SIZE / 2;
 	int middle_y = (v->y_pos & ~TILE_UNIT_MASK) + TILE_SIZE / 2;
-	byte middle_z = GetSlopePixelZ(middle_x, middle_y);
+	byte middle_z = GetSlopePixelZ(middle_x, middle_y, true);
 
 	/* middle_z == entry_z, no height change. */
 	if (middle_z == entry_z) return 0;
@@ -586,6 +586,25 @@ static uint FixVehicleInclination(Vehicle *v, Direction dir)
 	return 1U << GVF_GOINGUP_BIT;
 }
 
+/**
+ * Check whether the ground vehicles are at the correct Z-coordinate. When they
+ * are not, this will cause all kinds of problems later on as the vehicle might
+ * not get onto bridges and so on.
+ */
+static void CheckGroundVehiclesAtCorrectZ()
+{
+	for (Vehicle *v : Vehicle::Iterate()) {
+		if (v->IsGroundVehicle()) {
+			/*
+			 * Either the vehicle is not actually on the given tile, i.e. it is
+			 * in the wormhole of a bridge or a tunnel, or the Z-coordinate must
+			 * be the same as when it would be recalculated right now.
+			 */
+			assert(v->tile != TileVirtXY(v->x_pos, v->y_pos) || v->z_pos == GetSlopePixelZ(v->x_pos, v->y_pos, true));
+		}
+	}
+}
+
 /**
  * Checks for the possibility that a bridge may be on this tile
  * These are in fact all the tile types on which a bridge can be found
@@ -1440,7 +1459,7 @@ bool AfterLoadGame()
 					case DIAGDIR_SW: if ((v->x_pos & 0xF) != TILE_SIZE - 1) continue; break;
 					case DIAGDIR_NW: if ((v->y_pos & 0xF) !=  0)            continue; break;
 				}
-			} else if (v->z_pos > GetSlopePixelZ(v->x_pos, v->y_pos)) {
+			} else if (v->z_pos > GetTileMaxPixelZ(TileVirtXY(v->x_pos, v->y_pos))) {
 				v->tile = GetNorthernBridgeEnd(v->tile);
 				v->UpdatePosition();
 			} else {
@@ -2895,7 +2914,7 @@ bool AfterLoadGame()
 			if (!IsTunnelTile(vtile)) continue;
 
 			/* Are we actually in this tunnel? Or maybe a lower tunnel? */
-			if (GetSlopePixelZ(v->x_pos, v->y_pos) != v->z_pos) continue;
+			if (GetSlopePixelZ(v->x_pos, v->y_pos, true) != v->z_pos) continue;
 
 			/* What way are we going? */
 			const DiagDirection dir = GetTunnelBridgeDirection(vtile);
@@ -2974,6 +2993,23 @@ bool AfterLoadGame()
 		}
 	}
 
+	if (IsSavegameVersionBefore(SLV_CONSISTENT_PARTIAL_Z) && SlXvIsFeatureMissing(XSLFI_CONSISTENT_PARTIAL_Z)) {
+		/*
+		 * The logic of GetPartialPixelZ has been changed, so the resulting Zs on
+		 * the map are consistent. This requires that the Z position of some
+		 * vehicles is updated to reflect this new situation.
+		 *
+		 * This needs to be before SLV_158, because that performs asserts using
+		 * GetSlopePixelZ which internally uses GetPartialPixelZ.
+		 */
+		for (Vehicle *v : Vehicle::Iterate()) {
+			if (v->IsGroundVehicle() && TileVirtXY(v->x_pos, v->y_pos) == v->tile) {
+				/* Vehicle is on the ground, and not in a wormhole. */
+				v->z_pos = GetSlopePixelZ(v->x_pos, v->y_pos, true);
+			}
+		}
+	}
+
 	if (IsSavegameVersionBefore(SLV_158)) {
 		for (Vehicle *v : Vehicle::Iterate()) {
 			switch (v->type) {
@@ -3040,7 +3076,7 @@ bool AfterLoadGame()
 				/* In old versions, z_pos was 1 unit lower on bridge heads.
 				 * However, this invalid state could be converted to new savegames
 				 * by loading and saving the game in a new version. */
-				v->z_pos = GetSlopePixelZ(v->x_pos, v->y_pos);
+				v->z_pos = GetSlopePixelZ(v->x_pos, v->y_pos, true);
 				DiagDirection dir = GetTunnelBridgeDirection(v->tile);
 				if (v->type == VEH_TRAIN && !(v->vehstatus & VS_CRASHED) &&
 						v->direction != DiagDirToDir(dir)) {
@@ -3054,7 +3090,7 @@ bool AfterLoadGame()
 
 			/* If the vehicle is really above v->tile (not in a wormhole),
 			 * it should have set v->z_pos correctly. */
-			assert(v->tile != TileVirtXY(v->x_pos, v->y_pos) || v->z_pos == GetSlopePixelZ(v->x_pos, v->y_pos));
+			assert(v->tile != TileVirtXY(v->x_pos, v->y_pos) || v->z_pos == GetSlopePixelZ(v->x_pos, v->y_pos, true));
 		}
 
 		/* Fill Vehicle::cur_real_order_index */
@@ -4209,6 +4245,14 @@ bool AfterLoadGame()
 		AfterLoad_LinkGraphPauseControl();
 	}
 
+	if (SlXvIsFeatureMissing(XSLFI_CONSISTENT_PARTIAL_Z)) {
+		CheckGroundVehiclesAtCorrectZ();
+	} else {
+#ifdef _DEBUG
+		CheckGroundVehiclesAtCorrectZ();
+#endif
+	}
+
 	_game_load_cur_date_ymd = _cur_date_ymd;
 	_game_load_date_fract = _date_fract;
 	_game_load_tick_skip_counter = _tick_skip_counter;
diff --git a/src/saveload/extended_ver_sl.cpp b/src/saveload/extended_ver_sl.cpp
index 2918763a38..242be770f8 100644
--- a/src/saveload/extended_ver_sl.cpp
+++ b/src/saveload/extended_ver_sl.cpp
@@ -194,6 +194,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_LAST_LOADING_TICK,                XSCF_NULL,                2,   2, "last_loading_tick",                nullptr, nullptr, nullptr          },
 	{ XSLFI_SCRIPT_LEAGUE_TABLES,             XSCF_NULL,                1,   1, "script_league_tables",             nullptr, nullptr, "LEAE,LEAT"      },
 	{ XSLFI_VELOCITY_NAUTICAL,                XSCF_IGNORABLE_ALL,       1,   1, "velocity_nautical",                nullptr, nullptr, nullptr          },
+	{ XSLFI_CONSISTENT_PARTIAL_Z,             XSCF_NULL,                1,   1, "consistent_partial_z",             nullptr, nullptr, nullptr          },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, nullptr, nullptr, nullptr, nullptr },// This is the end marker
 };
 
diff --git a/src/saveload/extended_ver_sl.h b/src/saveload/extended_ver_sl.h
index bf64ae591f..d3d9811cdd 100644
--- a/src/saveload/extended_ver_sl.h
+++ b/src/saveload/extended_ver_sl.h
@@ -146,6 +146,7 @@ enum SlXvFeatureIndex {
 	XSLFI_LAST_LOADING_TICK,                      ///< See: SLV_LAST_LOADING_TICK
 	XSLFI_SCRIPT_LEAGUE_TABLES,                   ///< See: Scriptable league tables (PR #10001)
 	XSLFI_VELOCITY_NAUTICAL,                      ///< See: SLV_VELOCITY_NAUTICAL (PR #10594)
+	XSLFI_CONSISTENT_PARTIAL_Z,                   ///< See: SLV_CONSISTENT_PARTIAL_Z (PR #10570)
 
 	XSLFI_RIFF_HEADER_60_BIT,                     ///< Size field in RIFF chunk header is 60 bit
 	XSLFI_HEIGHT_8_BIT,                           ///< Map tile height is 8 bit instead of 4 bit, but savegame version may be before this became true in trunk
diff --git a/src/saveload/saveload_common.h b/src/saveload/saveload_common.h
index 10679d1d56..21619dd254 100644
--- a/src/saveload/saveload_common.h
+++ b/src/saveload/saveload_common.h
@@ -357,6 +357,7 @@ enum SaveLoadVersion : uint16 {
 	SLV_LINKGRAPH_EDGES,                    ///< 304  PR#10314 Explicitly store link graph edges destination.
 
 	SLV_VELOCITY_NAUTICAL,                  ///< 305  PR#10594 Separation of land and nautical velocity (knots!)
+	SLV_CONSISTENT_PARTIAL_Z,               ///< 306  PR#10570 Conversion from an inconsistent partial Z calculation for slopes, to one that is (more) consistent.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 
diff --git a/src/slope_func.h b/src/slope_func.h
index e37d9b4c41..5cf125f8c4 100644
--- a/src/slope_func.h
+++ b/src/slope_func.h
@@ -21,7 +21,7 @@
  * @param corner A #Corner.
  * @return true iff corner is in a valid range.
  */
-static inline bool IsValidCorner(Corner corner)
+static constexpr inline bool IsValidCorner(Corner corner)
 {
 	return IsInsideMM(corner, 0, CORNER_END);
 }
@@ -33,7 +33,7 @@ static inline bool IsValidCorner(Corner corner)
  * @param s The given #Slope.
  * @return True if the slope is steep, else false.
  */
-static inline bool IsSteepSlope(Slope s)
+static constexpr inline bool IsSteepSlope(Slope s)
 {
 	return (s & SLOPE_STEEP) != 0;
 }
@@ -44,7 +44,7 @@ static inline bool IsSteepSlope(Slope s)
  * @param s The given #Slope.
  * @return True if the slope is non-continuous, else false.
  */
-static inline bool IsHalftileSlope(Slope s)
+static constexpr inline bool IsHalftileSlope(Slope s)
 {
 	return (s & SLOPE_HALFTILE) != 0;
 }
@@ -57,7 +57,7 @@ static inline bool IsHalftileSlope(Slope s)
  * @param s A #Slope.
  * @return The slope s without its halftile slope.
  */
-static inline Slope RemoveHalftileSlope(Slope s)
+static constexpr inline Slope RemoveHalftileSlope(Slope s)
 {
 	return s & ~SLOPE_HALFTILE_MASK;
 }
@@ -145,7 +145,7 @@ static inline Corner GetHighestSlopeCorner(Slope s)
  * @param s The #Slope.
  * @return  The corner of the leveled halftile.
  */
-static inline Corner GetHalftileSlopeCorner(Slope s)
+static constexpr inline Corner GetHalftileSlopeCorner(Slope s)
 {
 	dbg_assert(IsHalftileSlope(s));
 	return (Corner)((s >> 6) & 3);
@@ -157,7 +157,7 @@ static inline Corner GetHalftileSlopeCorner(Slope s)
  * @param s The #Slope.
  * @return Relative height of highest corner.
  */
-static inline int GetSlopeMaxZ(Slope s)
+static constexpr inline int GetSlopeMaxZ(Slope s)
 {
 	if (s == SLOPE_FLAT) return 0;
 	if (IsSteepSlope(s)) return 2;
@@ -170,7 +170,7 @@ static inline int GetSlopeMaxZ(Slope s)
  * @param s The #Slope.
  * @return Relative height of highest corner.
  */
-static inline int GetSlopeMaxPixelZ(Slope s)
+static constexpr inline int GetSlopeMaxPixelZ(Slope s)
 {
 	return GetSlopeMaxZ(s) * TILE_HEIGHT;
 }
@@ -271,7 +271,7 @@ static inline Slope InclinedSlope(DiagDirection dir)
  * @param corner The #Corner of the halftile.
  * @return The #Slope s with the halftile slope added.
  */
-static inline Slope HalftileSlope(Slope s, Corner corner)
+static constexpr inline Slope HalftileSlope(Slope s, Corner corner)
 {
 	dbg_assert(IsValidCorner(corner));
 	return (Slope)(s | SLOPE_HALFTILE | (corner << 6));
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index be59517812..5e9a730625 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -3668,7 +3668,7 @@ void StationPickerDrawSprite(int x, int y, StationType st, RailType railtype, Ro
 	DrawRailTileSeqInGUI(x, y, t, (st == STATION_WAYPOINT || st == STATION_ROADWAYPOINT) ? 0 : total_offset, 0, pal);
 }
 
-static int GetSlopePixelZ_Station(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Station(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	return GetTileMaxPixelZ(tile);
 }
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
new file mode 100644
index 0000000000..d028125ae9
--- /dev/null
+++ b/src/tests/CMakeLists.txt
@@ -0,0 +1,3 @@
+add_files(
+    landscape_partial_pixel_z.h
+)
diff --git a/src/tests/landscape_partial_pixel_z.h b/src/tests/landscape_partial_pixel_z.h
new file mode 100644
index 0000000000..a825709392
--- /dev/null
+++ b/src/tests/landscape_partial_pixel_z.h
@@ -0,0 +1,552 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file landscape_partial_pixel_z.h Tests for consistency/validity of the results of GetPartialPixelZ. */
+
+/**
+ * Check whether the addition of two slope's GetPartialPixelZ values results in
+ * the GetPartialPixelZ values of the expected slope.
+ * This iterates over all sub-pixel locations within a single tile.
+ * @param slope_expected The slope that is expected.
+ * @param slope_a The first slope of the addition.
+ * @param slope_b The second slope of the addition.
+ * @return True iff at all GetPartialPixelZ results are the same for each sub-tile position.
+ */
+constexpr bool CheckPartialPixelZSlopeAddition(Slope slope_expected, Slope slope_a, Slope slope_b)
+{
+	for (uint x = 0; x < TILE_SIZE; x++) {
+		for (uint y = 0; y < TILE_SIZE; y++) {
+			int z_a = InternalGetPartialPixelZ(x, y, slope_a);
+			int z_b = InternalGetPartialPixelZ(x, y, slope_b);
+			int z_result = InternalGetPartialPixelZ(x, y, slope_expected);
+			if (z_result != z_a + z_b) return false;
+		}
+	}
+	return true;
+}
+
+/* A one corner slope, plus the opposite three corner slope results in a flat but elevated slope. */
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_N, SLOPE_WSE));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_E, SLOPE_NWS));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_S, SLOPE_ENW));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_W, SLOPE_SEN));
+
+/* Diagonal slopes with their opposite slope result in a flat but elevated slope. */
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_NW, SLOPE_SE));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, SLOPE_SW, SLOPE_NE));
+
+/* Half tile slopes with their opposite half tile slope result in a flat but elevated slope. */
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, HalftileSlope(SLOPE_N, CORNER_N), HalftileSlope(SLOPE_S, CORNER_S)));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_ELEVATED, HalftileSlope(SLOPE_E, CORNER_E), HalftileSlope(SLOPE_W, CORNER_W)));
+
+/* Two opposite one corner slopes result in the two corner slope with opposite corners. */
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_NS, SLOPE_N, SLOPE_S));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_EW, SLOPE_E, SLOPE_W));
+
+/* A steep slope is a one corner slope on top of a three corner slope. */
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_STEEP_N, SLOPE_N, SLOPE_ENW));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_STEEP_E, SLOPE_E, SLOPE_SEN));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_STEEP_S, SLOPE_S, SLOPE_WSE));
+static_assert(CheckPartialPixelZSlopeAddition(SLOPE_STEEP_W, SLOPE_W, SLOPE_NWS));
+
+/* A half tile steep slope is a one corner half tile on top of a three corner slope. */
+static_assert(CheckPartialPixelZSlopeAddition(HalftileSlope(SLOPE_STEEP_N, CORNER_N), HalftileSlope(SLOPE_N, CORNER_N), SLOPE_ENW));
+static_assert(CheckPartialPixelZSlopeAddition(HalftileSlope(SLOPE_STEEP_E, CORNER_E), HalftileSlope(SLOPE_E, CORNER_E), SLOPE_SEN));
+static_assert(CheckPartialPixelZSlopeAddition(HalftileSlope(SLOPE_STEEP_S, CORNER_S), HalftileSlope(SLOPE_S, CORNER_S), SLOPE_WSE));
+static_assert(CheckPartialPixelZSlopeAddition(HalftileSlope(SLOPE_STEEP_W, CORNER_W), HalftileSlope(SLOPE_W, CORNER_W), SLOPE_NWS));
+
+
+/**
+ * Check whether the partial pixel Z values are the expected values. The arrays
+ * are as if the map is rotated 45 degrees counterclockwise.
+ * @param slope The slope that is to be checked.
+ * @param expected The expect partial pixels Z values.
+ * @return True iff at all GetPartialPixelZ results are the same as the expected Z-coordinates.
+ */
+constexpr bool CheckPartialPixelZ(Slope slope, std::array<int, TILE_SIZE * TILE_SIZE> expected)
+{
+	for (uint i = 0; i < expected.size(); i++) {
+		int actual = InternalGetPartialPixelZ(GB(i, 4, 4), GB(i, 0, 4), slope);
+		if (actual != expected[i]) return false;
+	}
+	return true;
+}
+
+/* One corner up slopes. */
+static_assert(CheckPartialPixelZ(SLOPE_N, {
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0,
+	7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0,
+	6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0,
+	6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0,
+	5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0,
+	5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0,
+	4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0,
+	4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}));
+
+static_assert(CheckPartialPixelZ(SLOPE_E, {
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7,
+	0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7,
+	0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
+	0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6,
+	0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,
+	0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5,
+	0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}));
+
+static_assert(CheckPartialPixelZ(SLOPE_S, {
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4,
+	0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4,
+	0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5,
+	0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,
+	0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6,
+	0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
+	0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7,
+	0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7}));
+
+static_assert(CheckPartialPixelZ(SLOPE_W, {
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0,
+	5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0,
+	5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0,
+	6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0, 0,
+	6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0, 0,
+	7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 0,
+	7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0}));
+
+/* Two corner up, diagonal slopes. */
+static_assert(CheckPartialPixelZ(SLOPE_NE, {
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}));
+
+static_assert(CheckPartialPixelZ(SLOPE_SE, {
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8}));
+
+static_assert(CheckPartialPixelZ(SLOPE_SW, {
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}));
+
+static_assert(CheckPartialPixelZ(SLOPE_NW, {
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0}));
+
+/* Two opposite corner up slopes. */
+static_assert(CheckPartialPixelZ(SLOPE_NS, {
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0,
+	7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1,
+	6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1,
+	6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2,
+	5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2,
+	5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3,
+	4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3,
+	4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4,
+	3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4,
+	3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5,
+	2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,
+	2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6,
+	1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
+	1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7,
+	0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7}));
+
+static_assert(CheckPartialPixelZ(SLOPE_EW, {
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7,
+	1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7,
+	1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
+	2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6,
+	2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,
+	3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5,
+	3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4,
+	4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 4,
+	4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3,
+	5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3,
+	5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2, 2,
+	6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1, 2,
+	6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1, 1,
+	7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0, 1,
+	7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0}));
+
+/* Three corner up slopes. */
+static_assert(CheckPartialPixelZ(SLOPE_ENW, {
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4,
+	8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4,
+	8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3,
+	8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3,
+	8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2,
+	8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2,
+	8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1,
+	8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1}));
+
+static_assert(CheckPartialPixelZ(SLOPE_SEN, {
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8,
+	3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8,
+	3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8,
+	2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8,
+	2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8,
+	1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8,
+	1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8}));
+
+static_assert(CheckPartialPixelZ(SLOPE_WSE, {
+	0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
+	1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
+	1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8,
+	2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8,
+	2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8,
+	3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8,
+	3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8,
+	4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8,
+	4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	5, 5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	5, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}));
+
+static_assert(CheckPartialPixelZ(SLOPE_NWS, {
+	8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0,
+	8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1,
+	8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1,
+	8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2,
+	8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2,
+	8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3,
+	8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3,
+	8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5, 4,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5, 5,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6, 5,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6, 6,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7, 6,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}));
+
+/* Normal half tile slopes. */
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_N, CORNER_N), {
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_E, CORNER_E), {
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_S, CORNER_S), {
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_W, CORNER_W), {
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 0}));
+
+/* Steep slopes. */
+static_assert(CheckPartialPixelZ(SLOPE_STEEP_N, {
+	16, 15, 15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,
+	15, 15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,
+	15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,
+	14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,
+	14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,
+	13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,
+	13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,
+	12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,
+	12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,
+	11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,
+	11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,
+	10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,
+	10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,
+	 9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,
+	 9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,
+	 8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1}));
+
+static_assert(CheckPartialPixelZ(SLOPE_STEEP_E, {
+	 8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16,
+	 8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15,
+	 7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15,
+	 7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14,
+	 6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14,
+	 6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13,
+	 5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13,
+	 5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12,
+	 4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12,
+	 4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11,
+	 3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11,
+	 3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10,
+	 2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10,
+	 2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9,
+	 1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,
+	 1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8}));
+
+static_assert(CheckPartialPixelZ(SLOPE_STEEP_S, {
+	 0,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,
+	 1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,
+	 1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,
+	 2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9,
+	 2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10,
+	 3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10,
+	 3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11,
+	 4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11,
+	 4,  5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12,
+	 5,  5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12,
+	 5,  6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13,
+	 6,  6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13,
+	 6,  7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14,
+	 7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14,
+	 7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15,
+	 8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15}));
+
+static_assert(CheckPartialPixelZ(SLOPE_STEEP_W, {
+	 8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1,  0,
+	 8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1,
+	 9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,
+	 9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,
+	10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,
+	10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,
+	11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,
+	11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,  4,
+	12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,  4,
+	12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,  5,
+	13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,  5,
+	13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,  6,
+	14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,  6,
+	14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,  7,
+	15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8,  7,
+	15, 15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10,  9,  9,  8,  8}));
+
+/* Half tile on top of steep slopes. */
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_STEEP_N, CORNER_N), {
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,
+	16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,
+	16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,
+	16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,
+	16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,
+	16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,
+	16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,
+	16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,
+	16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,
+	16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_STEEP_E, CORNER_E), {
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16,
+	 4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16,
+	 3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16,
+	 3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16,
+	 2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16,
+	 2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16,
+	 1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16,
+	 1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_STEEP_S, CORNER_S), {
+	 0,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,
+	 1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16,
+	 1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16,
+	 2,  2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16,
+	 2,  3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16,
+	 3,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16,
+	 3,  4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16,
+	 4,  4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16,
+	 4,  5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16,
+	 5,  5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 5,  6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 6,  6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 6,  7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 7,  7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 7,  8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
+	 8, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16}));
+
+static_assert(CheckPartialPixelZ(HalftileSlope(SLOPE_STEEP_W, CORNER_W), {
+	 8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1,  0,
+	16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,  1,
+	16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,  1,
+	16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,  2,
+	16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,  2,
+	16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,  3,
+	16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,  3,
+	16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,  4,
+	16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,  4,
+	16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,  5,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,  5,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,  6,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,  6,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,  7,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8,  7,
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,  8}));
diff --git a/src/tile_cmd.h b/src/tile_cmd.h
index f764f726de..7f0e07942a 100644
--- a/src/tile_cmd.h
+++ b/src/tile_cmd.h
@@ -81,7 +81,20 @@ struct DrawTileProcParams {
  * @param ti Information about the tile to draw
  */
 typedef void DrawTileProc(TileInfo *ti, DrawTileProcParams params);
-typedef int GetSlopeZProc(TileIndex tile, uint x, uint y);
+
+/**
+ * Tile callback function signature for obtaining the world \c Z coordinate of a given
+ * point of a tile.
+ *
+ * @param tile The queries tile for the Z coordinate.
+ * @param x World X coordinate in tile "units".
+ * @param y World Y coordinate in tile "units".
+ * @param ground_vehicle Whether to get the Z coordinate of the ground vehicle, or the ground.
+ * @return World Z coordinate at tile ground (vehicle) level, including slopes and foundations.
+ * @see GetSlopePixelZ
+ */
+typedef int GetSlopeZProc(TileIndex tile, uint x, uint y, bool ground_vehicle);
+
 typedef CommandCost ClearTileProc(TileIndex tile, DoCommandFlag flags);
 
 /**
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index 8486101f6c..5bc6ee0ae5 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -413,7 +413,7 @@ void DrawHouseImage(HouseID house_id, int left, int top, int right, int bottom)
 	}
 }
 
-static int GetSlopePixelZ_Town(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Town(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	return GetTileMaxPixelZ(tile);
 }
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 17408516ef..4bf31387d3 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -1462,7 +1462,7 @@ static CommandCost CmdBuildRailWagon(TileIndex tile, DoCommandFlag flags, const
 
 		v->x_pos = x;
 		v->y_pos = y;
-		v->z_pos = GetSlopePixelZ(x, y);
+		v->z_pos = GetSlopePixelZ(x, y, true);
 		v->owner = _current_company;
 		v->track = TRACK_BIT_DEPOT;
 		v->vehstatus = VS_HIDDEN | VS_DEFPAL;
@@ -1602,7 +1602,7 @@ CommandCost CmdBuildRailVehicle(TileIndex tile, DoCommandFlag flags, const Engin
 		v->owner = _current_company;
 		v->x_pos = x;
 		v->y_pos = y;
-		v->z_pos = GetSlopePixelZ(x, y);
+		v->z_pos = GetSlopePixelZ(x, y, true);
 		v->track = TRACK_BIT_DEPOT;
 		SetBit(v->flags, VRF_CONSIST_SPEED_REDUCTION);
 		v->vehstatus = VS_HIDDEN | VS_STOPPED | VS_DEFPAL;
@@ -5778,7 +5778,7 @@ bool TrainController(Train *v, Vehicle *nomove, bool reverse)
 
 				if (v->IsFrontEngine()) {
 					/* Check if track in front is free and see if we can leave wormhole. */
-					int z = GetSlopePixelZ(gp.x, gp.y) - v->z_pos;
+					int z = GetSlopePixelZ(gp.x, gp.y, true) - v->z_pos;
 					if (IsTileType(gp.new_tile, MP_TUNNELBRIDGE) &&	!(abs(z) > 2)) {
 						if (CheckTrainStayInWormHole(v, gp.new_tile)) {
 							v->cur_speed = 0;
diff --git a/src/tree_cmd.cpp b/src/tree_cmd.cpp
index 80c842258f..4434eb6313 100644
--- a/src/tree_cmd.cpp
+++ b/src/tree_cmd.cpp
@@ -788,7 +788,7 @@ static void DrawTile_Trees(TileInfo *ti, DrawTileProcParams params)
 }
 
 
-static int GetSlopePixelZ_Trees(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Trees(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	int z;
 	Slope tileh = GetTilePixelSlope(tile, &z);
diff --git a/src/tunnelbridge_cmd.cpp b/src/tunnelbridge_cmd.cpp
index e76155b0d9..2f4dd7529b 100644
--- a/src/tunnelbridge_cmd.cpp
+++ b/src/tunnelbridge_cmd.cpp
@@ -2563,7 +2563,7 @@ void DrawBridgeMiddle(const TileInfo *ti)
 }
 
 
-static int GetSlopePixelZ_TunnelBridge(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_TunnelBridge(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	int z;
 	Slope tileh = GetTilePixelSlope(tile, &z);
@@ -2572,34 +2572,27 @@ static int GetSlopePixelZ_TunnelBridge(TileIndex tile, uint x, uint y)
 	y &= 0xF;
 
 	if (IsTunnel(tile)) {
-		uint pos = (DiagDirToAxis(GetTunnelBridgeDirection(tile)) == AXIS_X ? y : x);
-
 		/* In the tunnel entrance? */
-		if (5 <= pos && pos <= 10) return z;
+		if (ground_vehicle) return z;
 	} else { // IsBridge(tile)
 		if (IsCustomBridgeHeadTile(tile)) {
 			return z + TILE_HEIGHT + (IsSteepSlope(tileh) ? TILE_HEIGHT : 0);
 		}
 
 		DiagDirection dir = GetTunnelBridgeDirection(tile);
-		uint pos = (DiagDirToAxis(dir) == AXIS_X ? y : x);
-
 		z += ApplyPixelFoundationToSlope(GetBridgeFoundation(tileh, DiagDirToAxis(dir)), &tileh);
 
 		/* On the bridge ramp? */
-		if (5 <= pos && pos <= 10) {
-			int delta;
-
+		if (ground_vehicle) {
 			if (tileh != SLOPE_FLAT) return z + TILE_HEIGHT;
 
 			switch (dir) {
 				default: NOT_REACHED();
-				case DIAGDIR_NE: delta = (TILE_SIZE - 1 - x) / 2; break;
-				case DIAGDIR_SE: delta = y / 2; break;
-				case DIAGDIR_SW: delta = x / 2; break;
-				case DIAGDIR_NW: delta = (TILE_SIZE - 1 - y) / 2; break;
+				case DIAGDIR_NE: tileh = SLOPE_NE; break;
+				case DIAGDIR_SE: tileh = SLOPE_SE; break;
+				case DIAGDIR_SW: tileh = SLOPE_SW; break;
+				case DIAGDIR_NW: tileh = SLOPE_NW; break;
 			}
-			return z + 1 + delta;
 		}
 	}
 
@@ -3063,6 +3056,29 @@ static void ChangeTileOwner_TunnelBridge(TileIndex tile, Owner old_owner, Owner
 	}
 }
 
+/**
+ * Helper to prepare the ground vehicle when entering a bridge. This get called
+ * when entering the bridge, at the last frame of travel on the bridge head.
+ * Our calling function gets called before UpdateInclination/UpdateZPosition,
+ * which normally controls the Z-coordinate. However, in the wormhole of the
+ * bridge the vehicle is in a strange state so UpdateInclination does not get
+ * called for the wormhole of the bridge and as such the going up/down bits
+ * would remain set. As such, this function clears those. In doing so, the call
+ * to UpdateInclination will not update the Z-coordinate, so that has to be
+ * done here as well.
+ * @param gv The ground vehicle entering the bridge.
+ */
+template <typename T>
+static void PrepareToEnterBridge(T *gv)
+{
+	if (HasBit(gv->gv_flags, GVF_GOINGUP_BIT)) {
+		gv->z_pos++;
+		ClrBit(gv->gv_flags, GVF_GOINGUP_BIT);
+	} else {
+		ClrBit(gv->gv_flags, GVF_GOINGDOWN_BIT);
+	}
+}
+
 /**
  * Frame when the 'enter tunnel' sound should be played. This is the second
  * frame on a tile, so the sound is played shortly after entering the tunnel
@@ -3098,7 +3114,7 @@ static VehicleEnterTileStatus VehicleEnter_TunnelBridge(Vehicle *v, TileIndex ti
 		y += offset.y;
 	}
 
-	int z = GetSlopePixelZ(x, y) - v->z_pos;
+	int z = GetSlopePixelZ(x, y, true) - v->z_pos;
 
 	if (abs(z) > 2) return VETSB_CANNOT_ENTER;
 
@@ -3188,8 +3204,7 @@ static VehicleEnterTileStatus VehicleEnter_TunnelBridge(Vehicle *v, TileIndex ti
 					Train *t = Train::From(v);
 					t->track = TRACK_BIT_WORMHOLE;
 					SetBit(t->First()->flags, VRF_CONSIST_SPEED_REDUCTION);
-					ClrBit(t->gv_flags, GVF_GOINGUP_BIT);
-					ClrBit(t->gv_flags, GVF_GOINGDOWN_BIT);
+					PrepareToEnterBridge(t);
 					break;
 				}
 
@@ -3205,9 +3220,7 @@ static VehicleEnterTileStatus VehicleEnter_TunnelBridge(Vehicle *v, TileIndex ti
 					}
 					rv->InvalidateImageCache();
 					rv->state = RVSB_WORMHOLE;
-					/* There are no slopes inside bridges / tunnels. */
-					ClrBit(rv->gv_flags, GVF_GOINGUP_BIT);
-					ClrBit(rv->gv_flags, GVF_GOINGDOWN_BIT);
+					PrepareToEnterBridge(rv);
 					break;
 				}
 
diff --git a/src/void_cmd.cpp b/src/void_cmd.cpp
index fc3895c422..d492eefe8b 100644
--- a/src/void_cmd.cpp
+++ b/src/void_cmd.cpp
@@ -25,7 +25,7 @@ static void DrawTile_Void(TileInfo *ti, DrawTileProcParams params)
 }
 
 
-static int GetSlopePixelZ_Void(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Void(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	/* This function may be called on tiles outside the map, don't assume
 	 * that 'tile' is a valid tile index. See GetSlopePixelZOutsideMap. */
diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index 5a67678ffa..c515acb82f 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -997,7 +997,7 @@ void DrawShipDepotSprite(int x, int y, Axis axis, DepotPart part)
 }
 
 
-static int GetSlopePixelZ_Water(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Water(TileIndex tile, uint x, uint y, bool ground_vehicle)
 {
 	int z;
 	Slope tileh = GetTilePixelSlope(tile, &z);