Feature: Allow stations and roadstops under bridges.

Bridges above stations will have pillars excluded if they conflict with the station layout.

Partly based on the system implemented in JGRPP.

Co-authored-by: <su@angel-island.zone>

src/lang/english.txt

@@ -5262,6 +5262,11 @@ STR_ERROR_START_AND_END_MUST_BE_IN                              :{WHITE}Start an
 STR_ERROR_ENDS_OF_BRIDGE_MUST_BOTH                              :{WHITE}... ends of bridge must both be on land
 STR_ERROR_BRIDGE_TOO_LONG                                       :{WHITE}... bridge too long
 STR_ERROR_BRIDGE_THROUGH_MAP_BORDER                             :{WHITE}Bridge would end out of the map
+STR_ERROR_BRIDGE_TOO_LOW_FOR_STATION                            :{WHITE}Bridge is too low for station
+STR_ERROR_BRIDGE_TOO_LOW_FOR_ROADSTOP                           :{WHITE}Bridge is too low for road stop
+STR_ERROR_BRIDGE_TOO_LOW_FOR_BUOY                               :{WHITE}Bridge is too low for buoy
+STR_ERROR_BRIDGE_TOO_LOW_FOR_RAIL_WAYPOINT                      :{WHITE}Bridge is too low for rail waypoint
+STR_ERROR_BRIDGE_TOO_LOW_FOR_ROAD_WAYPOINT                      :{WHITE}Bridge is too low for road waypoint
 
 # Tunnel related errors
 STR_ERROR_CAN_T_BUILD_TUNNEL_HERE                               :{WHITE}Can't build tunnel here...

src/saveload/saveload.h

@@ -407,6 +407,7 @@ enum SaveLoadVersion : uint16_t {
 	SLV_INDUSTRY_NUM_VALID_HISTORY,         ///< 356  PR#14416 Store number of valid history records for industries.
 	SLV_INDUSTRY_ACCEPTED_HISTORY,          ///< 357  PR#14321 Add per-industry history of cargo delivered and waiting.
 	SLV_TOWN_SUPPLY_HISTORY,                ///< 358  PR#14461 Town supply history.
+	SLV_STATIONS_UNDER_BRIDGES,             ///< 359  PR#14477 Allow stations under bridges.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };

src/station_cmd.cpp

@@ -73,6 +73,7 @@
 #include "widgets/station_widget.h"
 
 #include "table/strings.h"
+#include "table/station_land.h"
 
 #include <bitset>
 
@@ -865,6 +866,95 @@ static CommandCost CheckFlatLandAirport(AirportTileTableIterator tile_iter, DoCo
 	return cost;
 }
 
+/**
+ * Get station-type-specific string for a bridge that is too low.
+ * @param type Station type.
+ * @return bridge too low string.
+ */
+static StringID GetBridgeTooLowMessageForStationType(StationType type)
+{
+	static constexpr std::array<StringID, to_underlying(StationType::End)> too_low_msgs = {
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_STATION, // Rail
+		INVALID_STRING_ID, // Airport
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_ROADSTOP, // Truck
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_ROADSTOP, // Bus
+		INVALID_STRING_ID, // Oilrig
+		INVALID_STRING_ID, // Dock
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_BUOY, // Buoy
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_RAIL_WAYPOINT, // RailWaypoint
+		STR_ERROR_BRIDGE_TOO_LOW_FOR_ROAD_WAYPOINT, // RoadWaypoint
+	};
+	return too_low_msgs[to_underlying(type)];
+};
+
+/**
+ * Test if a bridge can be built above a station.
+ * @param tile Tile to test.
+ * @param spec Custom station spec to test.
+ * @param type Type of station.
+ * @param layout Layout piece of road station to test.
+ * @param bridge_height Height of bridge to test.
+ * @param disallowed_msg Error message if bridge is disallowed.
+ * @return Command result.
+ */
+static CommandCost IsStationBridgeAboveOk(TileIndex tile, std::span<const BridgeableTileInfo> bridgeable_info, StationType type, StationGfx layout, int bridge_height, StringID disallowed_msg = INVALID_STRING_ID)
+{
+	int height = layout < std::size(bridgeable_info) ? bridgeable_info[layout].height : 0;
+
+	if (height == 0) {
+		if (disallowed_msg != INVALID_STRING_ID) return CommandCost{disallowed_msg};
+		/* Get normal error message associated with clearing the tile. */
+		return Command<CMD_LANDSCAPE_CLEAR>::Do(DoCommandFlag::Auto, tile);
+	}
+	if (GetTileMaxZ(tile) + height > bridge_height) return CommandCost{GetBridgeTooLowMessageForStationType(type)};
+
+	return CommandCost{};
+}
+
+/**
+ * Get bridgeable tile information for a station type.
+ * @param type Station type.
+ * @return bridgeable tile information.
+ */
+static std::span<const BridgeableTileInfo> GetStationBridgeableTileInfo(StationType type)
+{
+	return _station_bridgeable_info[to_underlying(type)];
+}
+
+/**
+ * Test if a rail station can be built below a bridge.
+ * @param tile Tile to test.
+ * @param spec Custom station spec to test.
+ * @param type Type of rail station.
+ * @param layout Layout piece of station to test.
+ * @return Command result.
+ */
+CommandCost IsRailStationBridgeAboveOk(TileIndex tile, const StationSpec *spec, StationType type, StationGfx layout)
+{
+	if (!IsBridgeAbove(tile)) return CommandCost();
+
+	TileIndex rampsouth = GetSouthernBridgeEnd(tile);
+	auto bridgeable_info = spec == nullptr ? GetStationBridgeableTileInfo(type) : spec->bridgeable_info;
+	return IsStationBridgeAboveOk(tile, bridgeable_info, type, layout, GetBridgeHeight(rampsouth), STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
+}
+
+/**
+ * Test if a road station can be built below a bridge.
+ * @param tile Tile to test.
+ * @param spec Custom roadstop spec to test.
+ * @param type Type of road station.
+ * @param layout Layout piece of station to test.
+ * @return Command result.
+ */
+CommandCost IsRoadStationBridgeAboveOk(TileIndex tile, const RoadStopSpec *spec, StationType type, StationGfx layout)
+{
+	if (!IsBridgeAbove(tile)) return CommandCost();
+
+	TileIndex rampsouth = GetSouthernBridgeEnd(tile);
+	auto bridgeable_info = spec == nullptr ? GetStationBridgeableTileInfo(type) : spec->bridgeable_info;
+	return IsStationBridgeAboveOk(tile, bridgeable_info, type, layout, GetBridgeHeight(rampsouth), STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
+}
+
 /**
  * Checks if a rail station can be built at the given tile.
  * @param tile_cur Tile to check.
@@ -889,7 +979,7 @@ static CommandCost CheckFlatLandRailStation(TileIndex tile_cur, TileIndex north_
 	const StationSpec *statspec = StationClass::Get(spec_class)->GetSpec(spec_index);
 	bool slope_cb = statspec != nullptr && statspec->callback_mask.Test(StationCallbackMask::SlopeCheck);
 
-	CommandCost ret = CheckBuildableTile(tile_cur, invalid_dirs, allowed_z, false);
+	CommandCost ret = CheckBuildableTile(tile_cur, invalid_dirs, allowed_z, false, false);
 	if (ret.Failed()) return ret;
 	cost.AddCost(ret.GetCost());
 
@@ -954,6 +1044,7 @@ static CommandCost CheckFlatLandRailStation(TileIndex tile_cur, TileIndex north_
  * Checks if a road stop can be built at the given tile.
  * @param cur_tile Tile to check.
  * @param allowed_z Height allowed for the tile. If allowed_z is negative, it will be set to the height of this tile.
+ * @param spec Spec of road stop to be built.
  * @param flags Operation to perform.
  * @param invalid_dirs Prohibited directions (set of DiagDirections).
  * @param is_drive_through True if trying to build a drive-through station.
@@ -963,14 +1054,17 @@ static CommandCost CheckFlatLandRailStation(TileIndex tile_cur, TileIndex north_
  * @param rt Road type to build, may be INVALID_ROADTYPE if an existing road is required.
  * @return The cost in case of success, or an error code if it failed.
  */
-static CommandCost CheckFlatLandRoadStop(TileIndex cur_tile, int &allowed_z, DoCommandFlags flags, DiagDirections invalid_dirs, bool is_drive_through, StationType station_type, Axis axis, StationID *station, RoadType rt)
+static CommandCost CheckFlatLandRoadStop(TileIndex cur_tile, int &allowed_z, const RoadStopSpec *spec, DoCommandFlags flags, DiagDirections invalid_dirs, bool is_drive_through, StationType station_type, Axis axis, StationID *station, RoadType rt)
 {
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 
-	CommandCost ret = CheckBuildableTile(cur_tile, invalid_dirs, allowed_z, !is_drive_through);
+	CommandCost ret = CheckBuildableTile(cur_tile, invalid_dirs, allowed_z, !is_drive_through, false);
 	if (ret.Failed()) return ret;
 	cost.AddCost(ret.GetCost());
 
+	ret = IsRoadStationBridgeAboveOk(cur_tile, spec, station_type, is_drive_through ? GFX_TRUCK_BUS_DRIVETHROUGH_OFFSET + axis : FindFirstBit(invalid_dirs.base()));
+	if (ret.Failed()) return ret;
+
 	/* If station is set, then we have special handling to allow building on top of already existing stations.
 	 * Station points to StationID::Invalid() if we can build on any station.
 	 * Or it points to a station if we're only allowed to build on exactly that station. */
@@ -1346,6 +1440,9 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 		w_org = numtracks;
 	}
 
+	/* Check if the first tile and the last tile are valid */
+	if (!IsValidTile(tile_org) || TileAddWrap(tile_org, w_org - 1, h_org - 1) == INVALID_TILE) return CMD_ERROR;
+
 	bool reuse = (station_to_join != NEW_STATION);
 	if (!reuse) station_to_join = StationID::Invalid();
 	bool distant_join = (station_to_join != StationID::Invalid());
@@ -1376,8 +1473,24 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 		if (ret.Failed()) return ret;
 	}
 
-	/* Check if we can allocate a custom stationspec to this station */
 	const StationSpec *statspec = StationClass::Get(spec_class)->GetSpec(spec_index);
+	TileIndexDiff tile_delta = TileOffsByAxis(axis); // offset to go to the next platform tile
+	TileIndexDiff track_delta = TileOffsByAxis(OtherAxis(axis)); // offset to go to the next track
+
+	RailStationTileLayout stl{statspec, numtracks, plat_len};
+	auto it = stl.begin();
+	TileIndex tile_track = tile_org;
+	for (uint i = 0; i != numtracks; ++i) {
+		TileIndex tile = tile_track;
+		for (uint j = 0; j != plat_len; ++j) {
+			ret = IsRailStationBridgeAboveOk(tile, statspec, StationType::Rail, *it++ + axis);
+			if (ret.Failed()) return ret;
+			tile += tile_delta;
+		}
+		tile_track += track_delta;
+	}
+
+	/* Check if we can allocate a custom stationspec to this station */
 	auto specindex = AllocateSpecToStation(statspec, st, flags.Test(DoCommandFlag::Execute));
 	if (!specindex.has_value()) return CommandCost(STR_ERROR_TOO_MANY_STATION_SPECS);
 
@@ -1407,21 +1520,15 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 			st->cached_anim_triggers.Set(statspec->animation.triggers);
 		}
 
-		TileIndexDiff tile_delta = TileOffsByAxis(axis); // offset to go to the next platform tile
-		TileIndexDiff track_delta = TileOffsByAxis(OtherAxis(axis)); // offset to go to the next track
 		Track track = AxisToTrack(axis);
 
-		RailStationTileLayout stl{statspec, numtracks, plat_len};
 		auto it = stl.begin();
 
-		uint8_t numtracks_orig = numtracks;
-
 		Company *c = Company::Get(st->owner);
 		TileIndex tile_track = tile_org;
-		do {
+		for (uint i = 0; i != numtracks; ++i) {
 			TileIndex tile = tile_track;
-			int w = plat_len;
-			do {
+			for (uint j = 0; j != plat_len; ++j) {
 				if (IsRailStationTile(tile) && HasStationReservation(tile)) {
 					/* Check for trains having a reservation for this tile. */
 					Train *v = GetTrainForReservation(tile, AxisToTrack(GetRailStationAxis(tile)));
@@ -1451,7 +1558,7 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 
 				if (statspec != nullptr) {
 					/* Use a fixed axis for GetPlatformInfo as our platforms / numtracks are always the right way around */
-					uint32_t platinfo = GetPlatformInfo(AXIS_X, GetStationGfx(tile), plat_len, numtracks_orig, plat_len - w, numtracks_orig - numtracks, false);
+					uint32_t platinfo = GetPlatformInfo(AXIS_X, GetStationGfx(tile), plat_len, numtracks, j, i, false);
 
 					/* As the station is not yet completely finished, the station does not yet exist. */
 					uint16_t callback = GetStationCallback(CBID_STATION_BUILD_TILE_LAYOUT, platinfo, 0, statspec, nullptr, tile);
@@ -1473,11 +1580,11 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 				c->infrastructure.station++;
 
 				tile += tile_delta;
-			} while (--w);
+			}
 			AddTrackToSignalBuffer(tile_track, track, _current_company);
 			YapfNotifyTrackLayoutChange(tile_track, track);
 			tile_track += track_delta;
-		} while (--numtracks);
+		}
 
 		for (uint i = 0; i < affected_vehicles.size(); ++i) {
 			/* Restore reservations of trains. */
@@ -1487,9 +1594,9 @@ CommandCost CmdBuildRailStation(DoCommandFlags flags, TileIndex tile_org, RailTy
 		/* Check whether we need to expand the reservation of trains already on the station. */
 		TileArea update_reservation_area;
 		if (axis == AXIS_X) {
-			update_reservation_area = TileArea(tile_org, 1, numtracks_orig);
+			update_reservation_area = TileArea(tile_org, 1, numtracks);
 		} else {
-			update_reservation_area = TileArea(tile_org, numtracks_orig, 1);
+			update_reservation_area = TileArea(tile_org, numtracks, 1);
 		}
 
 		for (TileIndex tile : update_reservation_area) {
@@ -1889,6 +1996,7 @@ static CommandCost FindJoiningRoadStop(StationID existing_stop, StationID statio
  * @param flags Operation to perform.
  * @param is_drive_through True if trying to build a drive-through station.
  * @param station_type Station type (bus, truck or road waypoint).
+ * @param roadstopspec Spec of road stop being built.
  * @param axis Axis of a drive-through road stop.
  * @param ddir Entrance direction (#DiagDirection) for normal stops. Converted to the axis for drive-through stops.
  * @param station StationID to be queried and returned if available.
@@ -1896,7 +2004,7 @@ static CommandCost FindJoiningRoadStop(StationID existing_stop, StationID statio
  * @param unit_cost The cost to build one road stop of the current type.
  * @return The cost in case of success, or an error code if it failed.
  */
-CommandCost CalculateRoadStopCost(TileArea tile_area, DoCommandFlags flags, bool is_drive_through, StationType station_type, Axis axis, DiagDirection ddir, StationID *est, RoadType rt, Money unit_cost)
+CommandCost CalculateRoadStopCost(TileArea tile_area, DoCommandFlags flags, bool is_drive_through, StationType station_type, const RoadStopSpec *roadstopspec, Axis axis, DiagDirection ddir, StationID *est, RoadType rt, Money unit_cost)
 {
 	DiagDirections invalid_dirs{};
 	if (is_drive_through) {
@@ -1910,7 +2018,7 @@ CommandCost CalculateRoadStopCost(TileArea tile_area, DoCommandFlags flags, bool
 	int allowed_z = -1;
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 	for (TileIndex cur_tile : tile_area) {
-		CommandCost ret = CheckFlatLandRoadStop(cur_tile, allowed_z, flags, invalid_dirs, is_drive_through, station_type, axis, est, rt);
+		CommandCost ret = CheckFlatLandRoadStop(cur_tile, allowed_z, roadstopspec, flags, invalid_dirs, is_drive_through, station_type, axis, est, rt);
 		if (ret.Failed()) return ret;
 
 		bool is_preexisting_roadstop = IsTileType(cur_tile, MP_STATION) && IsAnyRoadStop(cur_tile);
@@ -1991,7 +2099,7 @@ CommandCost CmdBuildRoadStop(DoCommandFlags flags, TileIndex tile, uint8_t width
 		unit_cost = _price[is_truck_stop ? PR_BUILD_STATION_TRUCK : PR_BUILD_STATION_BUS];
 	}
 	StationID est = StationID::Invalid();
-	CommandCost cost = CalculateRoadStopCost(roadstop_area, flags, is_drive_through, is_truck_stop ? StationType::Truck : StationType::Bus, axis, ddir, &est, rt, unit_cost);
+	CommandCost cost = CalculateRoadStopCost(roadstop_area, flags, is_drive_through, is_truck_stop ? StationType::Truck : StationType::Bus, roadstopspec, axis, ddir, &est, rt, unit_cost);
 	if (cost.Failed()) return cost;
 
 	Station *st = nullptr;
@@ -2976,8 +3084,6 @@ static CommandCost RemoveDock(TileIndex tile, DoCommandFlags flags)
 	return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_CLEAR_STATION_DOCK]);
 }
 
-#include "table/station_land.h"
-
 /**
  * Get station tile layout for a station type and its station gfx.
  * @param st Station type to draw.
@@ -3056,6 +3162,18 @@ bool SplitGroundSpriteForOverlay(const TileInfo *ti, SpriteID *ground, RailTrack
 	return true;
 }
 
+/**
+ * Get blocked pillar information for a station tile.
+ * @param bridgeable_info
+ * @param layout Tile layout of rail station.
+ * @return blocked pillar information.
+ */
+static BridgePillarFlags GetStationBlockedPillars(std::span<const BridgeableTileInfo> bridgeable_info, uint8_t layout)
+{
+	if (layout < std::size(bridgeable_info)) return bridgeable_info[layout].disallowed_pillars;
+	return BRIDGEPILLARFLAGS_ALL;
+}
+
 /**
  * Draw custom station foundations for a NewGRF station if provided.
  * @param statspec Custom NewGRF station.
@@ -3137,6 +3255,7 @@ static void DrawTile_Station(TileInfo *ti)
 	BaseStation *st = nullptr;
 	const StationSpec *statspec = nullptr;
 	uint tile_layout = 0;
+	auto bridgeable_info = GetStationBridgeableTileInfo(GetStationType(ti->tile));
 
 	if (HasStationRail(ti->tile)) {
 		rti = GetRailTypeInfo(GetRailType(ti->tile));
@@ -3165,6 +3284,7 @@ static void DrawTile_Station(TileInfo *ti)
 				}
 			}
 		}
+		if (statspec != nullptr) bridgeable_info = statspec->bridgeable_info;
 	} else {
 		total_offset = 0;
 	}
@@ -3355,6 +3475,7 @@ static void DrawTile_Station(TileInfo *ti)
 				DrawGroundSprite(ground + view, PAL_NONE);
 			}
 		}
+		if (stopspec != nullptr) bridgeable_info = stopspec->bridgeable_info;
 
 		if (stopspec == nullptr || !stopspec->flags.Test(RoadStopSpecFlag::NoCatenary)) {
 			/* Draw road, tram catenary */
@@ -3368,6 +3489,7 @@ static void DrawTile_Station(TileInfo *ti)
 	}
 
 	DrawRailTileSeq(ti, t, TO_BUILDINGS, total_offset, relocation, palette);
+	DrawBridgeMiddle(ti, GetStationBlockedPillars(bridgeable_info, GetStationGfx(ti->tile)));
 }
 
 void StationPickerDrawSprite(int x, int y, StationType st, RailType railtype, RoadType roadtype, int image)
@@ -5150,6 +5272,29 @@ uint FlowStatMap::GetFlowFromVia(StationID from, StationID via) const
 	return i->second.GetShare(via);
 }
 
+static CommandCost CheckBuildAbove_Station(TileIndex tile, DoCommandFlags, Axis, int height)
+{
+	StationType type = GetStationType(tile);
+	auto bridgeable_info = GetStationBridgeableTileInfo(type);
+
+	switch (type) {
+		case StationType::Rail:
+		case StationType::RailWaypoint:
+			if (const StationSpec *spec = GetStationSpec(tile); spec != nullptr) bridgeable_info = spec->bridgeable_info;
+			break;
+
+		case StationType::Bus:
+		case StationType::Truck:
+		case StationType::RoadWaypoint:
+			if (const RoadStopSpec *spec = GetRoadStopSpec(tile); spec != nullptr) bridgeable_info = spec->bridgeable_info;
+			break;
+
+		default: break;
+	}
+
+	return IsStationBridgeAboveOk(tile, bridgeable_info, type, GetStationGfx(tile), height);
+}
+
 extern const TileTypeProcs _tile_type_station_procs = {
 	DrawTile_Station,           // draw_tile_proc
 	GetSlopePixelZ_Station,     // get_slope_z_proc
@@ -5165,5 +5310,5 @@ extern const TileTypeProcs _tile_type_station_procs = {
 	VehicleEnter_Station,       // vehicle_enter_tile_proc
 	GetFoundation_Station,      // get_foundation_proc
 	TerraformTile_Station,      // terraform_tile_proc
-	nullptr, // check_build_above_proc
+	CheckBuildAbove_Station, // check_build_above_proc
 };

src/table/station_land.h

@@ -902,3 +902,53 @@ static const std::array<std::span<const DrawTileSpriteSpan>, to_underlying(Stati
 	_station_display_datas_waypoint,
 	_station_display_datas_road_waypoint,
 }};
+
+static const BridgeableTileInfo _station_bridgeable_info_rail[] = {
+	{2, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE}}, // X-axis empty platform.
+	{2, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE}}, // Y-axis empty platform.
+	{2, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE}}, // X-axis small building.
+	{2, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE}}, // Y-axis small building.
+	{5, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE, BridgePillarFlag::EdgeSE, BridgePillarFlag::CornerE, BridgePillarFlag::CornerS}}, // X large building north.
+	{5, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE, BridgePillarFlag::EdgeSW, BridgePillarFlag::CornerS, BridgePillarFlag::CornerW}}, // Y large building north.
+	{5, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE, BridgePillarFlag::EdgeNW, BridgePillarFlag::CornerN, BridgePillarFlag::CornerW}}, // X large building south.
+	{5, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE, BridgePillarFlag::EdgeNE, BridgePillarFlag::CornerN, BridgePillarFlag::CornerE}}, // Y large building south.
+};
+
+static const BridgeableTileInfo _station_bridgeable_info_waypoint[] = {
+	{2, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE}}, // X-axis waypoint.
+	{2, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE}}, // Y-axis waypoint.
+};
+
+static const BridgeableTileInfo _station_bridgeable_info_buoy[] = {
+	{1, {}},
+};
+
+static const BridgeableTileInfo _station_bridgeable_info_roadstop[] = {
+	{2, {BridgePillarFlag::EdgeNE}}, // NE bay.
+	{2, {BridgePillarFlag::EdgeSE}}, // SE bay.
+	{2, {BridgePillarFlag::EdgeSW}}, // SW bay.
+	{2, {BridgePillarFlag::EdgeNW}}, // NW bay.
+	{2, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE}}, // X-axis drive-through.
+	{2, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE}}, // Y-axis drive-through.
+};
+
+static const BridgeableTileInfo _station_bridgeable_info_road_waypoint[] = {
+	{}, // NE bay (unused)
+	{}, // SE bay (unused)
+	{}, // SW bay (unused)
+	{}, // NW bay (unused)
+	{2, {BridgePillarFlag::EdgeSW, BridgePillarFlag::EdgeNE}}, // X-axis waypoint.
+	{2, {BridgePillarFlag::EdgeNW, BridgePillarFlag::EdgeSE}}, // Y-axis waypoint.
+};
+
+static const std::array<std::span<const BridgeableTileInfo>, to_underlying(StationType::End)> _station_bridgeable_info = {{
+	_station_bridgeable_info_rail, // Rail
+	{}, // Airport
+	_station_bridgeable_info_roadstop, // Truck
+	_station_bridgeable_info_roadstop, // Bus
+	{}, // Oilrig
+	{}, // Dock
+	_station_bridgeable_info_buoy, // Buoy
+	_station_bridgeable_info_waypoint, // RailWaypoint
+	_station_bridgeable_info_road_waypoint, // RoadWaypoint
+}};

src/tunnelbridge_cmd.cpp

@@ -280,7 +280,6 @@ static CommandCost CheckBuildAbove(TileIndex tile, DoCommandFlags flags, Axis ax
 	if (_tile_type_procs[GetTileType(tile)]->check_build_above_proc != nullptr) {
 		return _tile_type_procs[GetTileType(tile)]->check_build_above_proc(tile, flags, axis, height);
 	}
-
 	/* A tile without a handler must be cleared. */
 	return Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile);
 }
@@ -441,6 +440,14 @@ CommandCost CmdBuildBridge(DoCommandFlags flags, TileIndex tile_end, TileIndex t
 		/* If bridge belonged to bankrupt company, it has a new owner now */
 		is_new_owner = (owner == OWNER_NONE);
 		if (is_new_owner) owner = company;
+
+		/* Check if the new bridge is compatible with tiles underneath. */
+		TileIndexDiff delta = (direction == AXIS_X ? TileDiffXY(1, 0) : TileDiffXY(0, 1));
+		for (TileIndex tile = tile_start + delta; tile != tile_end; tile += delta) {
+			CommandCost ret = CheckBuildAbove(tile, flags, direction, z_start + 1);
+			if (ret.Failed()) return ret;
+			cost.AddCost(ret.GetCost());
+		}
 	} else {
 		/* Build a new bridge. */
 
@@ -491,7 +498,7 @@ CommandCost CmdBuildBridge(DoCommandFlags flags, TileIndex tile_end, TileIndex t
 				return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
 			}
 
-			ret = CheckBuildAbove(tile, flags, direction, z_start);
+			ret = CheckBuildAbove(tile, flags, direction, z_start + 1);
 			if (ret.Failed()) return ret;
 			cost.AddCost(ret.GetCost());
 

src/waypoint_cmd.cpp

@@ -175,14 +175,14 @@ static CommandCost IsValidTileForWaypoint(TileIndex tile, Axis axis, StationID *
 		return CommandCost(STR_ERROR_FLAT_LAND_REQUIRED);
 	}
 
-	if (IsBridgeAbove(tile)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
-
 	return CommandCost();
 }
 
 extern CommandCost FindJoiningWaypoint(StationID existing_station, StationID station_to_join, bool adjacent, TileArea ta, Waypoint **wp, bool is_road);
 extern CommandCost CanExpandRailStation(const BaseStation *st, TileArea &new_ta);
-extern CommandCost CalculateRoadStopCost(TileArea tile_area, DoCommandFlags flags, bool is_drive_through, StationType station_type, Axis axis, DiagDirection ddir, StationID *est, RoadType rt, Money unit_cost);
+extern CommandCost CalculateRoadStopCost(TileArea tile_area, DoCommandFlags flags, bool is_drive_through, StationType station_type, const RoadStopSpec *roadstopspec, Axis axis, DiagDirection ddir, StationID *est, RoadType rt, Money unit_cost);
+extern CommandCost IsRailStationBridgeAboveOk(TileIndex tile, const StationSpec *spec, StationType type, StationGfx layout);
+
 extern CommandCost RemoveRoadWaypointStop(TileIndex tile, DoCommandFlags flags, int replacement_spec_index);
 
 /**
@@ -231,12 +231,19 @@ CommandCost CmdBuildRailWaypoint(DoCommandFlags flags, TileIndex start_tile, Axi
 	/* Make sure the area below consists of clear tiles. (OR tiles belonging to a certain rail station) */
 	StationID est = StationID::Invalid();
 
+	const StationSpec *spec = StationClass::Get(spec_class)->GetSpec(spec_index);
+	RailStationTileLayout stl{spec, count, 1};
+	auto it = stl.begin();
+
 	/* Check whether the tiles we're building on are valid rail or not. */
 	TileIndexDiff offset = TileOffsByAxis(OtherAxis(axis));
 	for (int i = 0; i < count; i++) {
 		TileIndex tile = start_tile + i * offset;
 		CommandCost ret = IsValidTileForWaypoint(tile, axis, &est);
 		if (ret.Failed()) return ret;
+
+		ret = IsRailStationBridgeAboveOk(tile, spec, StationType::RailWaypoint, *it++);
+		if (ret.Failed()) return ret;
 	}
 
 	Waypoint *wp = nullptr;
@@ -264,7 +271,6 @@ CommandCost CmdBuildRailWaypoint(DoCommandFlags flags, TileIndex start_tile, Axi
 		if (!Waypoint::CanAllocateItem()) return CommandCost(STR_ERROR_TOO_MANY_STATIONS_LOADING);
 	}
 
-	const StationSpec *spec = StationClass::Get(spec_class)->GetSpec(spec_index);
 	auto specindex = AllocateSpecToStation(spec, wp, flags.Test(DoCommandFlag::Execute));
 	if (!specindex.has_value()) return CommandCost(STR_ERROR_TOO_MANY_STATION_SPECS);
 
@@ -289,7 +295,6 @@ CommandCost CmdBuildRailWaypoint(DoCommandFlags flags, TileIndex start_tile, Axi
 
 		wp->UpdateVirtCoord();
 
-		RailStationTileLayout stl{spec, count, 1};
 		auto it = stl.begin();
 
 		Company *c = Company::Get(wp->owner);
@@ -363,7 +368,7 @@ CommandCost CmdBuildRoadWaypoint(DoCommandFlags flags, TileIndex start_tile, Axi
 		unit_cost = _price[PR_BUILD_STATION_TRUCK];
 	}
 	StationID est = StationID::Invalid();
-	CommandCost cost = CalculateRoadStopCost(roadstop_area, flags, true, StationType::RoadWaypoint, axis, AxisToDiagDir(axis), &est, INVALID_ROADTYPE, unit_cost);
+	CommandCost cost = CalculateRoadStopCost(roadstop_area, flags, true, StationType::RoadWaypoint, roadstopspec, axis, AxisToDiagDir(axis), &est, INVALID_ROADTYPE, unit_cost);
 	if (cost.Failed()) return cost;
 
 	Waypoint *wp = nullptr;