(svn r25849) -Codechange: Introduce IsTileFlat to not compute full slope information for situations when we only want to know if a tile is flat or not (cirdan, LordAro)

11 files changed, 51 insertions, 27 deletions

diff --git a/src/clear_cmd.cpp b/src/clear_cmd.cpp
index 46598866f..858197c91 100644
--- a/src/clear_cmd.cpp
+++ b/src/clear_cmd.cpp
@@ -249,8 +249,7 @@ static void TileLoop_Clear(TileIndex tile)
 	/* If the tile is at any edge flood it to prevent maps without water. */
 	if (_settings_game.construction.freeform_edges && DistanceFromEdge(tile) == 1) {
 		int z;
-		Slope slope = GetTileSlope(tile, &z);
-		if (z == 0 && slope == SLOPE_FLAT) {
+		if (IsTileFlat(tile, &z) && z == 0) {
 			DoFloodTile(tile);
 			MarkTileDirtyByTile(tile);
 			return;
diff --git a/src/industry_cmd.cpp b/src/industry_cmd.cpp
index c29a00820..7841ce84c 100644
--- a/src/industry_cmd.cpp
+++ b/src/industry_cmd.cpp
@@ -1386,7 +1386,7 @@ static CommandCost CheckIfIndustryTilesAreFree(TileIndex tile, const IndustryTil
 
 		if (gfx == GFX_WATERTILE_SPECIALCHECK) {
 			if (!IsTileType(cur_tile, MP_WATER) ||
-					GetTileSlope(cur_tile) != SLOPE_FLAT) {
+					!IsTileFlat(cur_tile)) {
 				return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 			}
 		} else {
diff --git a/src/landscape.cpp b/src/landscape.cpp
index 2e3e3d52e..d69275dd3 100644
--- a/src/landscape.cpp
+++ b/src/landscape.cpp
@@ -937,8 +937,7 @@ static void CreateDesertOrRainForest()
 static bool FindSpring(TileIndex tile, void *user_data)
 {
 	int referenceHeight;
-	Slope s = GetTileSlope(tile, &referenceHeight);
-	if (s != SLOPE_FLAT || IsWaterTile(tile)) return false;
+	if (!IsTileFlat(tile, &referenceHeight) || IsWaterTile(tile)) return false;
 
 	/* In the tropics rivers start in the rainforest. */
 	if (_settings_game.game_creation.landscape == LT_TROPIC && GetTropicZone(tile) != TROPICZONE_RAINFOREST) return false;
@@ -974,7 +973,7 @@ static bool FindSpring(TileIndex tile, void *user_data)
 static bool MakeLake(TileIndex tile, void *user_data)
 {
 	uint height = *(uint*)user_data;
-	if (!IsValidTile(tile) || TileHeight(tile) != height || GetTileSlope(tile) != SLOPE_FLAT) return false;
+	if (!IsValidTile(tile) || TileHeight(tile) != height || !IsTileFlat(tile)) return false;
 	if (_settings_game.game_creation.landscape == LT_TROPIC && GetTropicZone(tile) == TROPICZONE_DESERT) return false;
 
 	for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
@@ -1123,7 +1122,7 @@ static bool FlowRiver(bool *marks, TileIndex spring, TileIndex begin)
 		queue.pop_front();
 
 		uint height2 = TileHeight(end);
-		if (GetTileSlope(end) == SLOPE_FLAT && (height2 < height || (height2 == height && IsWaterTile(end)))) {
+		if (IsTileFlat(end) && (height2 < height || (height2 == height && IsWaterTile(end)))) {
 			found = true;
 			break;
 		}
@@ -1150,7 +1149,7 @@ static bool FlowRiver(bool *marks, TileIndex spring, TileIndex begin)
 
 		if (IsValidTile(lakeCenter) &&
 				/* A river, or lake, can only be built on flat slopes. */
-				GetTileSlope(lakeCenter) == SLOPE_FLAT &&
+				IsTileFlat(lakeCenter) &&
 				/* We want the lake to be built at the height of the river. */
 				TileHeight(begin) == TileHeight(lakeCenter) &&
 				/* We don't want the lake at the entry of the valley. */
diff --git a/src/object_cmd.cpp b/src/object_cmd.cpp
index 59fc3f5c4..20a392ca6 100644
--- a/src/object_cmd.cpp
+++ b/src/object_cmd.cpp
@@ -303,7 +303,7 @@ CommandCost CmdBuildObject(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 	switch (type) {
 		case OBJECT_TRANSMITTER:
 		case OBJECT_LIGHTHOUSE:
-			if (GetTileSlope(tile) != SLOPE_FLAT) return_cmd_error(STR_ERROR_FLAT_LAND_REQUIRED);
+			if (!IsTileFlat(tile)) return_cmd_error(STR_ERROR_FLAT_LAND_REQUIRED);
 			break;
 
 		case OBJECT_OWNED_LAND:
@@ -673,7 +673,7 @@ void GenerateObjects()
 		TileIndex tile = RandomTile();
 
 		int h;
-		if (IsTileType(tile, MP_CLEAR) && GetTileSlope(tile, &h) == SLOPE_FLAT && h >= 4 && !IsBridgeAbove(tile)) {
+		if (IsTileType(tile, MP_CLEAR) && IsTileFlat(tile, &h) && h >= 4 && !IsBridgeAbove(tile)) {
 			TileIndex t = tile;
 			if (CircularTileSearch(&t, 9, HasTransmitter, NULL)) continue;
 
@@ -710,7 +710,7 @@ void GenerateObjects()
 
 		for (int j = 0; j < 19; j++) {
 			int h;
-			if (IsTileType(tile, MP_CLEAR) && GetTileSlope(tile, &h) == SLOPE_FLAT && h <= 2 && !IsBridgeAbove(tile)) {
+			if (IsTileType(tile, MP_CLEAR) && IsTileFlat(tile, &h) && h <= 2 && !IsBridgeAbove(tile)) {
 				BuildObject(OBJECT_LIGHTHOUSE, tile);
 				IncreaseGeneratingWorldProgress(GWP_OBJECT);
 				lighthouses_to_build--;
diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
index 96b568b82..67b2f8975 100644
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -74,7 +74,7 @@ void SetWaterClassDependingOnSurroundings(TileIndex t, bool include_invalid_wate
 {
 	/* If the slope is not flat, we always assume 'land' (if allowed). Also for one-corner-raised-shores.
 	 * Note: Wrt. autosloping under industry tiles this is the most fool-proof behaviour. */
-	if (GetTileSlope(t) != SLOPE_FLAT) {
+	if (!IsTileFlat(t)) {
 		if (include_invalid_water_class) {
 			SetWaterClass(t, WATER_CLASS_INVALID);
 			return;
@@ -1106,7 +1106,7 @@ bool AfterLoadGame()
 						if (GB(_m[t].m5, 3, 2) == 0) {
 							MakeClear(t, CLEAR_GRASS, 3);
 						} else {
-							if (GetTileSlope(t) != SLOPE_FLAT) {
+							if (!IsTileFlat(t)) {
 								MakeShore(t);
 							} else {
 								if (GetTileOwner(t) == OWNER_WATER) {
@@ -1712,7 +1712,7 @@ bool AfterLoadGame()
 		 * on its neighbouring tiles. Done after river and canal updates to
 		 * ensure neighbours are correct. */
 		for (TileIndex t = 0; t < map_size; t++) {
-			if (GetTileSlope(t) != SLOPE_FLAT) continue;
+			if (!IsTileFlat(t)) continue;
 
 			if (IsTileType(t, MP_WATER) && IsLock(t)) SetWaterClassDependingOnSurroundings(t, false);
 			if (IsTileType(t, MP_STATION) && (IsDock(t) || IsBuoy(t))) SetWaterClassDependingOnSurroundings(t, false);
@@ -2390,7 +2390,7 @@ bool AfterLoadGame()
 	if (IsSavegameVersionBefore(149)) {
 		for (TileIndex t = 0; t < map_size; t++) {
 			if (!IsTileType(t, MP_STATION)) continue;
-			if (!IsBuoy(t) && !IsOilRig(t) && !(IsDock(t) && GetTileSlope(t) == SLOPE_FLAT)) {
+			if (!IsBuoy(t) && !IsOilRig(t) && !(IsDock(t) && IsTileFlat(t))) {
 				SetWaterClass(t, WATER_CLASS_INVALID);
 			}
 		}
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index c57e4382d..19f7b3e64 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -2471,7 +2471,7 @@ CommandCost CmdBuildDock(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 	TileIndex tile_cur = tile + TileOffsByDiagDir(direction);
 
-	if (!IsTileType(tile_cur, MP_WATER) || GetTileSlope(tile_cur) != SLOPE_FLAT) {
+	if (!IsTileType(tile_cur, MP_WATER) || !IsTileFlat(tile_cur)) {
 		return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	}
 
@@ -2484,7 +2484,7 @@ CommandCost CmdBuildDock(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 	if (ret.Failed()) return ret;
 
 	tile_cur += TileOffsByDiagDir(direction);
-	if (!IsTileType(tile_cur, MP_WATER) || GetTileSlope(tile_cur) != SLOPE_FLAT) {
+	if (!IsTileType(tile_cur, MP_WATER) || !IsTileFlat(tile_cur)) {
 		return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	}
 
@@ -3069,7 +3069,7 @@ static void TileLoop_Station(TileIndex tile)
 			break;
 
 		case STATION_DOCK:
-			if (GetTileSlope(tile) != SLOPE_FLAT) break; // only handle water part
+			if (!IsTileFlat(tile)) break; // only handle water part
 			/* FALL THROUGH */
 		case STATION_OILRIG: //(station part)
 		case STATION_BUOY:
diff --git a/src/tile_map.cpp b/src/tile_map.cpp
index 86670c88a..1e30ba0d9 100644
--- a/src/tile_map.cpp
+++ b/src/tile_map.cpp
@@ -59,6 +59,30 @@ Slope GetTileSlope(TileIndex tile, int *h)
 }
 
 /**
+ * Check if a given tile is flat
+ * @param tile Tile to check
+ * @param h If not \c NULL, pointer to storage of z height (only if tile is flat)
+ * @return Whether the tile is flat
+ */
+bool IsTileFlat(TileIndex tile, int *h)
+{
+	assert(tile < MapSize());
+
+	if (!IsInnerTile(tile)) {
+		if (h != NULL) *h = TileHeight(tile);
+		return true;
+	}
+
+	uint z = TileHeight(tile);
+	if (TileHeight(tile + TileDiffXY(1, 0)) != z) return false;
+	if (TileHeight(tile + TileDiffXY(0, 1)) != z) return false;
+	if (TileHeight(tile + TileDiffXY(1, 1)) != z) return false;
+
+	if (h != NULL) *h = z;
+	return true;
+}
+
+/**
  * Get bottom height of the tile
  * @param tile Tile to compute height of
  * @return Minimum height of the tile
diff --git a/src/tile_map.h b/src/tile_map.h
index f9c7a2ac9..98863eb59 100644
--- a/src/tile_map.h
+++ b/src/tile_map.h
@@ -247,6 +247,8 @@ Slope GetTileSlope(TileIndex tile, int *h = NULL);
 int GetTileZ(TileIndex tile);
 int GetTileMaxZ(TileIndex tile);
 
+bool IsTileFlat(TileIndex tile, int *h = NULL);
+
 /**
  * Return the slope of a given tile
  * @param tile Tile to compute slope of
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index 6d469ba06..7ab9dcdad 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -1411,7 +1411,7 @@ static bool GrowTown(Town *t)
 		tile = t->xy;
 		for (ptr = _town_coord_mod; ptr != endof(_town_coord_mod); ++ptr) {
 			/* Only work with plain land that not already has a house */
-			if (!IsTileType(tile, MP_HOUSE) && GetTileSlope(tile) == SLOPE_FLAT) {
+			if (!IsTileType(tile, MP_HOUSE) && IsTileFlat(tile)) {
 				if (DoCommand(tile, 0, 0, DC_AUTO | DC_NO_WATER, CMD_LANDSCAPE_CLEAR).Succeeded()) {
 					DoCommand(tile, GenRandomRoadBits(), t->index, DC_EXEC | DC_AUTO, CMD_BUILD_ROAD);
 					cur_company.Restore();
@@ -1574,7 +1574,7 @@ static CommandCost TownCanBePlacedHere(TileIndex tile)
 	}
 
 	/* Can only build on clear flat areas, possibly with trees. */
-	if ((!IsTileType(tile, MP_CLEAR) && !IsTileType(tile, MP_TREES)) || GetTileSlope(tile) != SLOPE_FLAT) {
+	if ((!IsTileType(tile, MP_CLEAR) && !IsTileType(tile, MP_TREES)) || !IsTileFlat(tile)) {
 		return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	}
 
@@ -1775,7 +1775,7 @@ static bool FindFurthestFromWater(TileIndex tile, void *user_data)
 	uint dist = GetClosestWaterDistance(tile, true);
 
 	if (IsTileType(tile, MP_CLEAR) &&
-			GetTileSlope(tile) == SLOPE_FLAT &&
+			IsTileFlat(tile) &&
 			IsTileAlignedToGrid(tile, sp->layout) &&
 			dist > sp->max_dist) {
 		sp->tile = tile;
diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index b99741cfe..263731937 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -110,7 +110,7 @@ CommandCost CmdBuildShipDepot(TileIndex tile, DoCommandFlag flags, uint32 p1, ui
 	if ((MayHaveBridgeAbove(tile) && IsBridgeAbove(tile)) ||
 		(MayHaveBridgeAbove(tile2) && IsBridgeAbove(tile2))) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
 
-	if (GetTileSlope(tile) != SLOPE_FLAT || GetTileSlope(tile2) != SLOPE_FLAT) {
+	if (!IsTileFlat(tile) || !IsTileFlat(tile2)) {
 		/* Prevent depots on rapids */
 		return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	}
@@ -270,7 +270,7 @@ static CommandCost DoBuildLock(TileIndex tile, DiagDirection dir, DoCommandFlag
 		cost.AddCost(ret);
 		cost.AddCost(_price[PR_BUILD_CANAL]);
 	}
-	if (GetTileSlope(tile - delta) != SLOPE_FLAT) {
+	if (!IsTileFlat(tile - delta)) {
 		return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
 	}
 
@@ -283,7 +283,7 @@ static CommandCost DoBuildLock(TileIndex tile, DiagDirection dir, DoCommandFlag
 		cost.AddCost(ret);
 		cost.AddCost(_price[PR_BUILD_CANAL]);
 	}
-	if (GetTileSlope(tile + delta) != SLOPE_FLAT) {
+	if (!IsTileFlat(tile + delta)) {
 		return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
 	}
 
@@ -590,7 +590,7 @@ bool IsWateredTile(TileIndex tile, Direction from)
 
 				return IsTileOnWater(tile);
 			}
-			return (IsDock(tile) && GetTileSlope(tile) == SLOPE_FLAT) || IsBuoy(tile);
+			return (IsDock(tile) && IsTileFlat(tile)) || IsBuoy(tile);
 
 		case MP_INDUSTRY: {
 			/* Do not draw waterborders inside of industries.
@@ -1240,7 +1240,7 @@ static TrackStatus GetTileTrackStatus_Water(TileIndex tile, TransportType mode,
 	if (mode != TRANSPORT_WATER) return 0;
 
 	switch (GetWaterTileType(tile)) {
-		case WATER_TILE_CLEAR: ts = (GetTileSlope(tile) == SLOPE_FLAT) ? TRACK_BIT_ALL : TRACK_BIT_NONE; break;
+		case WATER_TILE_CLEAR: ts = IsTileFlat(tile) ? TRACK_BIT_ALL : TRACK_BIT_NONE; break;
 		case WATER_TILE_COAST: ts = (TrackBits)coast_tracks[GetTileSlope(tile) & 0xF]; break;
 		case WATER_TILE_LOCK:  ts = DiagDirToDiagTrackBits(GetLockDirection(tile)); break;
 		case WATER_TILE_DEPOT: ts = AxisToTrackBits(GetShipDepotAxis(tile)); break;
diff --git a/src/waypoint_cmd.cpp b/src/waypoint_cmd.cpp
index 35d7745c7..1a3d6e6e9 100644
--- a/src/waypoint_cmd.cpp
+++ b/src/waypoint_cmd.cpp
@@ -289,7 +289,7 @@ CommandCost CmdBuildBuoy(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 	if (tile == 0 || !HasTileWaterGround(tile)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	if (MayHaveBridgeAbove(tile) && IsBridgeAbove(tile)) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
 
-	if (GetTileSlope(tile) != SLOPE_FLAT) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
+	if (!IsTileFlat(tile)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 
 	/* Check if there is an already existing, deleted, waypoint close to us that we can reuse. */
 	Waypoint *wp = FindDeletedWaypointCloseTo(tile, STR_SV_STNAME_BUOY, OWNER_NONE);