(svn r15278) -Fix [FS#2332]: test noise limit of nearest town instead of st->town

2 files changed, 63 insertions, 40 deletions

diff --git a/src/ai/api/ai_airport.cpp b/src/ai/api/ai_airport.cpp
index cb8693255..2b0c3155b 100644
--- a/src/ai/api/ai_airport.cpp
+++ b/src/ai/api/ai_airport.cpp
@@ -115,6 +115,7 @@
 
 /* static */ int AIAirport::GetNoiseLevelIncrease(TileIndex tile, AirportType type)
 {
+	extern Town *AirportGetNearestTown(const AirportFTAClass *afc, TileIndex airport_tile);
 	extern uint8 GetAirportNoiseLevelForTown(const AirportFTAClass *afc, TileIndex town_tile, TileIndex tile);
 
 	if (!::IsValidTile(tile)) return -1;
@@ -122,7 +123,7 @@
 
 	if (_settings_game.economy.station_noise_level) {
 		const AirportFTAClass *afc = ::GetAirport(type);
-		const Town *t = ::ClosestTownFromTile(tile, UINT_MAX);
+		const Town *t = AirportGetNearestTown(afc, tile);
 		return GetAirportNoiseLevelForTown(afc, t->xy, tile);
 	}
 
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index 8085af255..4f1c5363c 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -1751,6 +1751,32 @@ static const byte * const _airport_sections[] = {
 	_airport_sections_helistation        // Helistation
 };
 
+/**
+ * Computes the minimal distance from town's xy to any airport's tile.
+ * @param afc airport's description
+ * @param town_tile town's tile (t->xy)
+ * @param airport_tile st->airport_tile
+ * @return minimal manhattan distance from town_tile to any airport's tile
+ */
+static uint GetMinimalAirportDistanceToTile(const AirportFTAClass *afc, TileIndex town_tile, TileIndex airport_tile)
+{
+	uint ttx = TileX(town_tile); // X, Y of town
+	uint tty = TileY(town_tile);
+
+	uint atx = TileX(airport_tile); // X, Y of northern airport corner
+	uint aty = TileY(airport_tile);
+
+	uint btx = TileX(airport_tile) + afc->size_x - 1; // X, Y of southern corner
+	uint bty = TileY(airport_tile) + afc->size_y - 1;
+
+	/* if ttx < atx, dx = atx - ttx
+	 * if atx <= ttx <= btx, dx = 0
+	 * else, dx = ttx - btx (similiar for dy) */
+	uint dx = ttx < atx ? atx - ttx : (ttx <= btx ? 0 : ttx - btx);
+	uint dy = tty < aty ? aty - tty : (tty <= bty ? 0 : tty - bty);
+
+	return dx + dy;
+}
 
 /** Get a possible noise reduction factor based on distance from town center.
  * The further you get, the less noise you generate.
@@ -1762,44 +1788,11 @@ static const byte * const _airport_sections[] = {
  */
 uint8 GetAirportNoiseLevelForTown(const AirportFTAClass *afc, TileIndex town_tile, TileIndex tile)
 {
-	struct TileIndexDistance {
-		TileIndex index;
-		uint distance;
-	};
-
 	/* 0 cannot be accounted, and 1 is the lowest that can be reduced from town.
 	 * So no need to go any further*/
 	if (afc->noise_level < 2) return afc->noise_level;
 
-	uint distance;
-
-	/* Find the airport-to-be's closest corner to the town */
-	if (afc->size_x == 1 && afc->size_y == 1) {
-		distance = DistanceManhattan(town_tile, tile);  // ont tile, one corner, it's THE corner
-	} else {
-		/* calculate manhattan distance to town of each side of the airport */
-		TileIndexDistance dist[4]; ///< Array that will contain all 4 corners in TileIndex and distance
-		uint min_tile = UINT_MAX;  ///< Sentinel value
-		uint min_indice = 4;
-
-		/* Based on the size of the airport, establish location of each corner*/
-		dist[0].index = tile; // north tile
-		dist[1].index = TileAddWrap(tile, afc->size_x - 1, afc->size_y - 1);  // south tile
-		dist[2].index = TileAddWrap(tile, afc->size_x - 1, 0);  // west tile
-		dist[3].index = TileAddWrap(tile, 0, afc->size_y - 1); //east tile
-
-		/* now, go and find the smallest one, thus the closest to town */
-		for (uint i = 0; i < 4; i++) {
-			dist[i].distance = DistanceManhattan(town_tile, dist[i].index);
-
-			if (dist[i].distance < min_tile) {
-				min_tile = dist[i].distance;  // here's a new candidate
-				min_indice = i;
-			}
-		}
-
-		distance = dist[min_indice].distance;
-	}
+	uint distance = GetMinimalAirportDistanceToTile(afc, town_tile, tile);
 
 	/* The steps for measuring noise reduction are based on the "magical" (and arbitrary) 8 base distance
 	 * adding the town_council_tolerance 4 times, as a way to graduate, depending of the tolerance.
@@ -1816,6 +1809,31 @@ uint8 GetAirportNoiseLevelForTown(const AirportFTAClass *afc, TileIndex town_til
 	return noise_reduction >= afc->noise_level ? 1 : afc->noise_level - noise_reduction;
 }
 
+/**
+ * Finds the town nearest to given airport. Based on minimal manhattan distance to any airport's tile.
+ * If two towns have the same distance, town with lower index is returned.
+ * @param afc airport's description
+ * @param airport_tile st->airport_tile
+ * @return nearest town to airport
+ */
+Town *AirportGetNearestTown(const AirportFTAClass *afc, TileIndex airport_tile)
+{
+	Town *t, *nearest = NULL;
+	uint add = afc->size_x + afc->size_y - 2; // GetMinimalAirportDistanceToTile can differ from DistanceManhattan by this much
+	uint mindist = UINT_MAX - add; // prevent overflow
+	FOR_ALL_TOWNS(t) {
+		if (DistanceManhattan(t->xy, airport_tile) < mindist + add) { // avoid calling GetMinimalAirportDistanceToTile too often
+			uint dist = GetMinimalAirportDistanceToTile(afc, t->xy, airport_tile);
+			if (dist < mindist) {
+				nearest = t;
+				mindist = dist;
+			}
+		}
+	}
+
+	return nearest;
+}
+
 
 /** Recalculate the noise generated by the airports of each town */
 void UpdateAirportsNoise()
@@ -1827,7 +1845,9 @@ void UpdateAirportsNoise()
 
 	FOR_ALL_STATIONS(st) {
 		if (st->airport_tile != INVALID_TILE) {
-			st->town->noise_reached += GetAirportNoiseLevelForTown(GetAirport(st->airport_type), st->town->xy, st->airport_tile);
+			const AirportFTAClass *afc = GetAirport(st->airport_type);
+			Town *nearest = AirportGetNearestTown(afc, st->airport_tile);
+			nearest->noise_reached += GetAirportNoiseLevelForTown(afc, nearest->xy, st->airport_tile);
 		}
 	}
 }
@@ -1871,14 +1891,15 @@ CommandCost CmdBuildAirport(TileIndex tile, uint32 flags, uint32 p1, uint32 p2,
 	if (CmdFailed(cost)) return cost;
 
 	/* Go get the final noise level, that is base noise minus factor from distance to town center */
-	uint newnoise_level = GetAirportNoiseLevelForTown(afc, t->xy, tile);
+	Town *nearest = AirportGetNearestTown(afc, tile);
+	uint newnoise_level = GetAirportNoiseLevelForTown(afc, nearest->xy, tile);
 
 	/* Check if local auth would allow a new airport */
 	bool authority_refused;
 
 	if (_settings_game.economy.station_noise_level) {
 		/* do not allow to build a new airport if this raise the town noise over the maximum allowed by town */
-		authority_refused = (t->noise_reached + newnoise_level) > t->MaxTownNoise();
+		authority_refused = (nearest->noise_reached + newnoise_level) > nearest->MaxTownNoise();
 	} else {
 		uint num = 0;
 		const Station *st;
@@ -1939,7 +1960,7 @@ CommandCost CmdBuildAirport(TileIndex tile, uint32 flags, uint32 p1, uint32 p2,
 
 	if (flags & DC_EXEC) {
 		/* Always add the noise, so there will be no need to recalculate when option toggles */
-		st->town->noise_reached += newnoise_level;
+		nearest->noise_reached += newnoise_level;
 
 		st->airport_tile = tile;
 		st->AddFacility(FACIL_AIRPORT, tile);
@@ -2020,7 +2041,8 @@ static CommandCost RemoveAirport(Station *st, uint32 flags)
 		/* Go get the final noise level, that is base noise minus factor from distance to town center.
 		 * And as for construction, always remove it, even if the patch is not set, in order to avoid the
 		 * need of recalculation */
-		st->town->noise_reached -= GetAirportNoiseLevelForTown(afc, st->town->xy, tile);
+		Town *nearest = AirportGetNearestTown(afc, tile);
+		nearest->noise_reached -= GetAirportNoiseLevelForTown(afc, nearest->xy, tile);
 
 		st->rect.AfterRemoveRect(st, tile, w, h);