--- a/src/bridge_map.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/bridge_map.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -7,6 +7,7 @@
 #include "bridge_map.h"
 #include "bridge.h"
 #include "variables.h"
+#include "landscape.h"
 
 
 TileIndex GetBridgeEnd(TileIndex tile, DiagDirection dir)
@@ -46,9 +47,6 @@
 	Slope tileh = GetTileSlope(t, &h);
 	Foundation f = GetBridgeFoundation(tileh, DiagDirToAxis(GetBridgeRampDirection(t)));
 
-	/* one height level extra if the ramp is on a flat foundation */
-	return
-		h + TILE_HEIGHT +
-		(IsLeveledFoundation(f) ? TILE_HEIGHT : 0) +
-		(IsSteepSlope(tileh) ? TILE_HEIGHT : 0);
+	/* one height level extra for the ramp */
+	return h + TILE_HEIGHT + ApplyFoundationToSlope(f, &tileh);
 }

--- a/src/elrail.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/elrail.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -213,6 +213,10 @@
 	/* Note that ti->tileh has already been adjusted for Foundations */
 	Slope tileh[TS_END] = { ti->tileh, SLOPE_FLAT };
 
+	/* Half tile slopes coincide only with horizontal/vertical track.
+	 * Faking a flat slope results in the correct sprites on positions. */
+	if (IsHalftileSlope(tileh[TS_HOME])) tileh[TS_HOME] = SLOPE_FLAT;
+
 	TLG tlg = GetTLG(ti->tile);
 	byte PCPstatus = 0;
 	byte OverridePCP = 0;
@@ -291,6 +295,10 @@
 
 		ApplyFoundationToSlope(foundation, &tileh[TS_NEIGHBOUR]);
 
+	/* Half tile slopes coincide only with horizontal/vertical track.
+	 * Faking a flat slope results in the correct sprites on positions. */
+		if (IsHalftileSlope(tileh[TS_NEIGHBOUR])) tileh[TS_NEIGHBOUR] = SLOPE_FLAT;
+
 		AdjustTileh(neighbour, &tileh[TS_NEIGHBOUR]);
 
 		/* If we have a straight (and level) track, we want a pylon only every 2 tiles

--- a/src/landscape.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/landscape.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -104,9 +104,31 @@
 
 uint GetPartialZ(int x, int y, Slope corners)
 {
+	if (IsHalftileSlope(corners)) {
+		switch (GetHalftileSlopeCorner(corners)) {
+			case CORNER_W:
+				if (x - y >= 0) return GetSlopeMaxZ(corners);
+				break;
+
+			case CORNER_S:
+				if (x - (y ^ 0xF) >= 0) return GetSlopeMaxZ(corners);
+				break;
+
+			case CORNER_E:
+				if (y - x >= 0) return GetSlopeMaxZ(corners);
+				break;
+
+			case CORNER_N:
+				if ((y ^ 0xF) - x >= 0) return GetSlopeMaxZ(corners);
+				break;
+
+			default: NOT_REACHED();
+		}
+	}
+
 	int z = 0;
 
-	switch (corners) {
+	switch (corners & ~SLOPE_HALFTILE_MASK) {
 	case SLOPE_W:
 		if (x - y >= 0)
 			z = (x - y) >> 1;
@@ -209,6 +231,8 @@
 /**
  * Determine the Z height of the corners of a specific tile edge
  *
+ * @note If a tile has a non-continuous halftile foundation, a corner can have different heights wrt. it's edges.
+ *
  * @pre z1 and z2 must be initialized (typ. with TileZ). The corner heights just get added.
  *
  * @param tileh The slope of the tile.
@@ -227,10 +251,14 @@
 		{SLOPE_W, SLOPE_N, SLOPE_STEEP_W, SLOPE_STEEP_N}, // DIAGDIR_NW, z1 = W, z2 = N
 	};
 
+	int halftile_test = (IsHalftileSlope(tileh) ? SlopeWithOneCornerRaised(GetHalftileSlopeCorner(tileh)) : 0);
+	if (halftile_test == corners[edge][0]) *z2 += TILE_HEIGHT; // The slope is non-continuous in z2. z2 is on the upper side.
+	if (halftile_test == corners[edge][1]) *z1 += TILE_HEIGHT; // The slope is non-continuous in z1. z1 is on the upper side.
+
 	if ((tileh & corners[edge][0]) != 0) *z1 += TILE_HEIGHT; // z1 is raised
 	if ((tileh & corners[edge][1]) != 0) *z2 += TILE_HEIGHT; // z2 is raised
-	if (tileh == corners[edge][2]) *z1 += TILE_HEIGHT; // z1 is highest corner of a steep slope
-	if (tileh == corners[edge][3]) *z2 += TILE_HEIGHT; // z2 is highest corner of a steep slope
+	if ((tileh & ~SLOPE_HALFTILE_MASK) == corners[edge][2]) *z1 += TILE_HEIGHT; // z1 is highest corner of a steep slope
+	if ((tileh & ~SLOPE_HALFTILE_MASK) == corners[edge][3]) *z2 += TILE_HEIGHT; // z2 is highest corner of a steep slope
 }
 
 static Slope GetFoundationSlope(TileIndex tile, uint* z)

--- a/src/npf.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/npf.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -192,18 +192,21 @@
 static uint NPFSlopeCost(AyStarNode* current)
 {
 	TileIndex next = current->tile + TileOffsByDiagDir(TrackdirToExitdir((Trackdir)current->direction));
-	int x,y;
-	int8 z1,z2;
 
-	x = TileX(current->tile) * TILE_SIZE;
-	y = TileY(current->tile) * TILE_SIZE;
-	/* get the height of the center of the current tile */
-	z1 = GetSlopeZ(x + TILE_SIZE / 2, y + TILE_SIZE / 2);
+	/* Get center of tiles */
+	int x1 = TileX(current->tile) * TILE_SIZE + TILE_SIZE / 2;
+	int y1 = TileY(current->tile) * TILE_SIZE + TILE_SIZE / 2;
+	int x2 = TileX(next) * TILE_SIZE + TILE_SIZE / 2;
+	int y2 = TileY(next) * TILE_SIZE + TILE_SIZE / 2;
 
-	x = TileX(next) * TILE_SIZE;
-	y = TileY(next) * TILE_SIZE;
-	/* get the height of the center of the next tile */
-	z2 = GetSlopeZ(x + TILE_SIZE / 2, y + TILE_SIZE / 2);
+	int dx4 = (x2 - x1) / 4;
+	int dy4 = (y2 - y1) / 4;
+
+	/* 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 = GetSlopeZ(x1 + dx4, y1 + dy4);
+	int z2 = GetSlopeZ(x2 - dx4, y2 - dy4);
 
 	if (z2 - z1 > 1) {
 		/* Slope up */

--- a/src/rail_cmd.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/rail_cmd.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -1238,6 +1238,22 @@
 
 #include "table/track_land.h"
 
+/**
+ * Get surface height in point (x,y)
+ * On tiles with halftile foundations move (x,y) to a save point wrt. track
+ */
+static uint GetSaveSlopeZ(uint x, uint y, Track track)
+{
+	switch (track) {
+		case TRACK_UPPER: x &= ~0xF; y &= ~0xF; break;
+		case TRACK_LOWER: x |=  0xF; y |=  0xF; break;
+		case TRACK_LEFT:  x |=  0xF; y &= ~0xF; break;
+		case TRACK_RIGHT: x &= ~0xF; y |=  0xF; break;
+		default: break;
+	}
+	return GetSlopeZ(x, y);
+}
+
 static void DrawSingleSignal(TileIndex tile, Track track, byte condition, uint image, uint pos)
 {
 	bool side = (_opt.road_side != 0) && _patches.signal_side;
@@ -1281,7 +1297,7 @@
 		sprite = _signal_base + (GetSignalType(tile, track) - 1) * 16 + GetSignalVariant(tile, track) * 64 + image + condition;
 	}
 
-	AddSortableSpriteToDraw(sprite, PAL_NONE, x, y, 1, 1, BB_HEIGHT_UNDER_BRIDGE, GetSlopeZ(x,y));
+	AddSortableSpriteToDraw(sprite, PAL_NONE, x, y, 1, 1, BB_HEIGHT_UNDER_BRIDGE, GetSaveSlopeZ(x, y, track));
 }
 
 static uint32 _drawtile_track_palette;
@@ -1338,6 +1354,7 @@
 {
 	int z = ti->z;
 	if (ti->tileh & SLOPE_W) z += TILE_HEIGHT;
+	if (IsSteepSlope(ti->tileh)) z += TILE_HEIGHT;
 	AddSortableSpriteToDraw(SPR_TRACK_FENCE_FLAT_VERT, _drawtile_track_palette,
 		ti->x + TILE_SIZE / 2, ti->y + TILE_SIZE / 2, 1, 1, 4, z);
 }
@@ -1349,6 +1366,7 @@
 {
 	int z = ti->z;
 	if (ti->tileh & SLOPE_E) z += TILE_HEIGHT;
+	if (IsSteepSlope(ti->tileh)) z += TILE_HEIGHT;
 	AddSortableSpriteToDraw(SPR_TRACK_FENCE_FLAT_VERT, _drawtile_track_palette,
 		ti->x + TILE_SIZE / 2, ti->y + TILE_SIZE / 2, 1, 1, 4, z);
 }
@@ -1360,6 +1378,7 @@
 {
 	int z = ti->z;
 	if (ti->tileh & SLOPE_N) z += TILE_HEIGHT;
+	if (IsSteepSlope(ti->tileh)) z += TILE_HEIGHT;
 	AddSortableSpriteToDraw(SPR_TRACK_FENCE_FLAT_HORZ, _drawtile_track_palette,
 		ti->x + TILE_SIZE / 2, ti->y + TILE_SIZE / 2, 1, 1, 4, z);
 }
@@ -1371,6 +1390,7 @@
 {
 	int z = ti->z;
 	if (ti->tileh & SLOPE_S) z += TILE_HEIGHT;
+	if (IsSteepSlope(ti->tileh)) z += TILE_HEIGHT;
 	AddSortableSpriteToDraw(SPR_TRACK_FENCE_FLAT_HORZ, _drawtile_track_palette,
 		ti->x + TILE_SIZE / 2, ti->y + TILE_SIZE / 2, 1, 1, 4, z);
 }

--- a/src/slope.h	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/slope.h	Sat Oct 20 16:50:48 2007 +0000
@@ -9,12 +9,31 @@
 #define SLOPE_H
 
 /**
+ * Enumeration of tile corners
+ */
+enum Corner {
+	CORNER_W = 0,
+	CORNER_S = 1,
+	CORNER_E = 2,
+	CORNER_N = 3,
+	CORNER_END
+};
+
+/**
  * Enumeration for the slope-type.
  *
  * This enumeration use the chars N,E,S,W corresponding the
  * direction north, east, south and west. The top corner of a tile
  * is the north-part of the tile. The whole slope is encoded with
  * 5 bits, 4 bits for each corner and 1 bit for a steep-flag.
+ *
+ * For halftile slopes an extra 3 bits are used to represent this
+ * properly; 1 bit for a halftile-flag and 2 bits to encode which
+ * extra side (corner) is leveled when the slope of the first 5
+ * bits is applied. This means that there can only be one leveled
+ * slope for steep slopes, which is logical because two leveled
+ * slopes would mean that it is not a steep slope as halftile
+ * slopes only span one height level.
  */
 enum Slope {
 	SLOPE_FLAT     = 0x00,                                  ///< a flat tile
@@ -37,18 +56,14 @@
 	SLOPE_STEEP_W  = SLOPE_STEEP | SLOPE_NWS,               ///< a steep slope falling to east (from west)
 	SLOPE_STEEP_S  = SLOPE_STEEP | SLOPE_WSE,               ///< a steep slope falling to north (from south)
 	SLOPE_STEEP_E  = SLOPE_STEEP | SLOPE_SEN,               ///< a steep slope falling to west (from east)
-	SLOPE_STEEP_N  = SLOPE_STEEP | SLOPE_ENW                ///< a steep slope falling to south (from north)
-};
+	SLOPE_STEEP_N  = SLOPE_STEEP | SLOPE_ENW,               ///< a steep slope falling to south (from north)
 
-/**
- * Enumeration of tile corners
- */
-enum Corner {
-	CORNER_W = 0,
-	CORNER_S = 1,
-	CORNER_E = 2,
-	CORNER_N = 3,
-	CORNER_END
+	SLOPE_HALFTILE = 0x20,                                  ///< one halftile is leveled (non continuous slope)
+	SLOPE_HALFTILE_MASK = 0xE0,                             ///< three bits used for halftile slopes
+	SLOPE_HALFTILE_W = SLOPE_HALFTILE | (CORNER_W << 6),    ///< the west halftile is leveled (non continuous slope)
+	SLOPE_HALFTILE_S = SLOPE_HALFTILE | (CORNER_S << 6),    ///< the south halftile is leveled (non continuous slope)
+	SLOPE_HALFTILE_E = SLOPE_HALFTILE | (CORNER_E << 6),    ///< the east halftile is leveled (non continuous slope)
+	SLOPE_HALFTILE_N = SLOPE_HALFTILE | (CORNER_N << 6),    ///< the north halftile is leveled (non continuous slope)
 };
 
 /**
@@ -74,43 +89,57 @@
 }
 
 /**
+ * Checks for non-continuous slope on halftile foundations.
+ *
+ * @param s The given #Slope.
+ * @return True if the slope is non-continuous, else false.
+ */
+static inline bool IsHalftileSlope(Slope s)
+{
+	return (s & SLOPE_HALFTILE) != 0;
+}
+
+/**
  * Return the complement of a slope.
  *
  * This method returns the complement of a slope. The complement of a
  * slope is a slope with raised corner which aren't raised in the given
  * slope.
  *
- * @pre The slope must not be steep.
+ * @pre The slope must neither be steep nor a halftile slope.
  * @param s The #Slope to get the complement.
  * @return a complement Slope of the given slope.
  */
 static inline Slope ComplementSlope(Slope s)
 {
-	assert(!IsSteepSlope(s));
+	assert(!IsSteepSlope(s) && !IsHalftileSlope(s));
 	return (Slope)(0xF ^ s);
 }
 
 /**
  * Tests if a slope has a highest corner (i.e. one corner raised or a steep slope).
  *
+ * Note: A halftile slope is ignored.
+ *
  * @param s The #Slope.
  * @return  true iff the slope has a highest corner.
  */
 static inline bool HasSlopeHighestCorner(Slope s)
 {
+	s = (Slope)(s & ~SLOPE_HALFTILE_MASK);
 	return IsSteepSlope(s) || (s == SLOPE_W) || (s == SLOPE_S) || (s == SLOPE_E) || (s == SLOPE_N);
 }
 
 /**
  * Returns the highest corner of a slope (one corner raised or a steep slope).
  *
- * @pre      The slope must be a slope with one corner raised or a steep slope.
+ * @pre      The slope must be a slope with one corner raised or a steep slope. A halftile slope is ignored.
  * @param s  The #Slope.
  * @return   Highest corner.
  */
 static inline Corner GetHighestSlopeCorner(Slope s)
 {
-	switch (s) {
+	switch (s & ~SLOPE_HALFTILE_MASK) {
 		case SLOPE_W:
 		case SLOPE_STEEP_W: return CORNER_W;
 		case SLOPE_S:
@@ -124,6 +153,19 @@
 }
 
 /**
+ * Returns the leveled halftile of a halftile slope.
+ *
+ * @pre     The slope must be a halftile slope.
+ * @param s The #Slope.
+ * @return  The corner of the leveled halftile.
+ */
+static inline Corner GetHalftileSlopeCorner(Slope s)
+{
+	assert(IsHalftileSlope(s));
+	return (Corner)((s >> 6) & 3);
+}
+
+/**
  * Returns the height of the highest corner of a slope relative to TileZ (= minimal height)
  *
  * @param s The #Slope.
@@ -170,6 +212,19 @@
 	return ComplementSlope(SlopeWithOneCornerRaised(corner));
 }
 
+/**
+ * Adds a halftile slope to a slope.
+ *
+ * @param s #Slope without a halftile slope.
+ * @param corner The #Corner of the halftile.
+ * @return The #Slope s with the halftile slope added.
+ */
+static inline Slope HalftileSlope(Slope s, Corner corner)
+{
+	assert(IsValidCorner(corner));
+	return (Slope)(s | SLOPE_HALFTILE | (corner << 6));
+}
+
 
 /**
  * Enumeration for Foundations.

--- a/src/viewport.cpp	Sat Oct 20 14:51:09 2007 +0000
+++ b/src/viewport.cpp	Sat Oct 20 16:50:48 2007 +0000
@@ -362,11 +362,17 @@
 	a = clamp(a, 0, (int)(MapMaxX() * TILE_SIZE) - 1);
 	b = clamp(b, 0, (int)(MapMaxY() * TILE_SIZE) - 1);
 
-	z = GetSlopeZ(a,     b    ) / 2;
-	z = GetSlopeZ(a + z, b + z) / 2;
-	z = GetSlopeZ(a + z, b + z) / 2;
-	z = GetSlopeZ(a + z, b + z) / 2;
-	z = GetSlopeZ(a + z, b + z) / 2;
+	/* (a, b) is the X/Y-world coordinate that belongs to (x,y) if the landscape would be completely flat on height 0.
+	 * Now find the Z-world coordinate by fix point iteration.
+	 * This is a bit tricky because the tile height is non-continuous at foundations.
+	 * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
+	 * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
+	 * So give it a z-malus of 4 in the first iterations.
+	 */
+	z = 0;
+	for (int i = 0; i < 5; i++) z = GetSlopeZ(a + max(z, 4u) - 4, b + max(z, 4u) - 4) / 2;
+	for (uint malus = 3; malus > 0; malus--) z = GetSlopeZ(a + max(z, malus) - malus, b + max(z, malus) - malus) / 2;
+	for (int i = 0; i < 5; i++) z = GetSlopeZ(a + z, b + z) / 2;
 
 	pt.x = a + z;
 	pt.y = b + z;