Feature: House placer mode to overbuild existing houses

src/lang/english.txt

@@ -2862,6 +2862,9 @@ STR_HOUSE_PICKER_PROTECT_TOOLTIP                                :Choose whether
 STR_HOUSE_PICKER_PROTECT_OFF                                    :Off
 STR_HOUSE_PICKER_PROTECT_ON                                     :On
 
+STR_HOUSE_PICKER_OVERBUILD                                      :Overbuild existing
+STR_HOUSE_PICKER_OVERBUILD_TOOLTIP                              :Choose whether to automatically remove an existing house on the tile where this house is placed
+
 STR_STATION_CLASS_DFLT                                          :Default
 STR_STATION_CLASS_DFLT_STATION                                  :Default station
 STR_STATION_CLASS_DFLT_ROADSTOP                                 :Default road stop

src/town_cmd.cpp

@@ -2902,9 +2902,10 @@ static bool TryBuildTownHouse(Town *t, TileIndex tile, TownExpandModes modes)
  * @param tile Tile on which to place the house.
  * @param HouseID The HouseID of the house spec.
  * @param is_protected Whether the house is protected from the town upgrading it.
+ * @param overbuild Whether to automatically demolish an existing house on this tile, if present.
  * @return Empty cost or an error.
  */
-CommandCost CmdPlaceHouse(DoCommandFlags flags, TileIndex tile, HouseID house, bool is_protected)
+CommandCost CmdPlaceHouse(DoCommandFlags flags, TileIndex tile, HouseID house, bool is_protected, bool overbuild)
 {
 	if (_game_mode != GM_EDITOR && _settings_game.economy.place_houses == PH_FORBIDDEN) return CMD_ERROR;
 
@@ -2914,39 +2915,45 @@ CommandCost CmdPlaceHouse(DoCommandFlags flags, TileIndex tile, HouseID house, b
 	const HouseSpec *hs = HouseSpec::Get(house);
 	if (!hs->enabled) return CMD_ERROR;
 
-	Town *t = ClosestTownFromTile(tile, UINT_MAX);
-
-	/* cannot build on these slopes... */
-	Slope slope = GetTileSlope(tile);
-	if (IsSteepSlope(slope)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
-
-	/* building under a bridge? */
-	if (IsBridgeAbove(tile)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
-
-	/* can we clear the land? */
-	CommandCost cost = Command<CMD_LANDSCAPE_CLEAR>::Do({DoCommandFlag::Auto, DoCommandFlag::NoWater}, tile);
-	if (!cost.Succeeded()) return cost;
-
 	int maxz = GetTileMaxZ(tile);
 
-	/* Make sure there is no slope? */
+	/* Check each tile of a multi-tile house. */
-	bool noslope = hs->building_flags.Test(BuildingFlag::NotSloped);
+	TileArea ta(tile, 1, 1);
-	if (noslope && slope != SLOPE_FLAT) return CommandCost(STR_ERROR_FLAT_LAND_REQUIRED);
-
-	TileArea ta = tile;
 	if (hs->building_flags.Test(BuildingFlag::Size2x2)) ta.Add(TileAddXY(tile, 1, 1));
 	if (hs->building_flags.Test(BuildingFlag::Size2x1)) ta.Add(TileAddByDiagDir(tile, DIAGDIR_SW));
 	if (hs->building_flags.Test(BuildingFlag::Size1x2)) ta.Add(TileAddByDiagDir(tile, DIAGDIR_SE));
 
-	/* Check additional tiles covered by this house. */
+	for (const TileIndex subtile : ta) {
-	for (const TileIndex &subtile : ta) {
+		/* Houses cannot be built on steep slopes. */
-		cost = Command<CMD_LANDSCAPE_CLEAR>::Do({DoCommandFlag::Auto, DoCommandFlag::NoWater}, subtile);
+		Slope slope = GetTileSlope(subtile);
-		if (!cost.Succeeded()) return cost;
+		if (IsSteepSlope(slope)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
 
-		if (!CheckBuildHouseSameZ(subtile, maxz, noslope)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
+		/* Houses cannot be built under bridges. */
+		if (IsBridgeAbove(subtile)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
+
+		/* Make sure there is no slope? */
+		bool noslope = hs->building_flags.Test(BuildingFlag::NotSloped);
+		if (noslope && slope != SLOPE_FLAT) return CommandCost(STR_ERROR_FLAT_LAND_REQUIRED);
+
+		/* All tiles of a multi-tile house must have the same z-level. */
+		if (GetTileMaxZ(subtile) != maxz) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
+
+		/* We might be overbuilding an existing house, otherwise check if we can clear land. */
+		if (!(overbuild && GetTileType(subtile) == MP_HOUSE)) {
+			CommandCost cost = Command<CMD_LANDSCAPE_CLEAR>::Do({DoCommandFlag::Auto, DoCommandFlag::NoWater}, subtile);
+			if (!cost.Succeeded()) return cost;
+		}
 	}
 
 	if (flags.Test(DoCommandFlag::Execute)) {
+		/* If overbuilding, clear any existing houses first. */
+		if (overbuild) {
+			for (const TileIndex &subtile : ta) {
+				if (GetTileType(subtile) == MP_HOUSE) ClearTownHouse(Town::GetByTile(subtile), subtile);
+			}
+		}
+
+		Town *t = ClosestTownFromTile(tile, UINT_MAX);
 		bool house_completed = _settings_game.economy.place_houses == PH_ALLOWED_CONSTRUCTED;
 		BuildTownHouse(t, tile, hs, house, Random(), house_completed, is_protected);
 	}

src/town_cmd.h

@@ -27,7 +27,7 @@ CommandCost CmdTownCargoGoal(DoCommandFlags flags, TownID town_id, TownAcceptanc
 CommandCost CmdTownSetText(DoCommandFlags flags, TownID town_id, const EncodedString &text);
 CommandCost CmdExpandTown(DoCommandFlags flags, TownID town_id, uint32_t grow_amount, TownExpandModes modes);
 CommandCost CmdDeleteTown(DoCommandFlags flags, TownID town_id);
-CommandCost CmdPlaceHouse(DoCommandFlags flags, TileIndex tile, HouseID house, bool house_protected);
+CommandCost CmdPlaceHouse(DoCommandFlags flags, TileIndex tile, HouseID house, bool house_protected, bool overbuild);
 
 DEF_CMD_TRAIT(CMD_FOUND_TOWN,       CmdFoundTown,      CommandFlags({CommandFlag::Deity, CommandFlag::NoTest}),  CMDT_LANDSCAPE_CONSTRUCTION) // founding random town can fail only in exec run
 DEF_CMD_TRAIT(CMD_RENAME_TOWN,      CmdRenameTown,     CommandFlags({CommandFlag::Deity, CommandFlag::Server}),  CMDT_OTHER_MANAGEMENT)

src/town_gui.cpp

@@ -1629,6 +1629,7 @@ static CargoTypes GetProducedCargoOfHouse(const HouseSpec *hs)
 struct BuildHouseWindow : public PickerWindow {
 	std::string house_info{};
 	static inline bool house_protected;
+	static inline bool overbuild;
 
 	BuildHouseWindow(WindowDesc &desc, Window *parent) : PickerWindow(desc, parent, 0, HousePickerCallbacks::instance)
 	{
@@ -1743,6 +1744,14 @@ struct BuildHouseWindow : public PickerWindow {
 				this->SetDirty();
 				break;
 
+			case WID_BH_OVERBUILD_TOGGLE:
+				BuildHouseWindow::overbuild = !BuildHouseWindow::overbuild;
+				this->SetWidgetLoweredState(WID_BH_OVERBUILD_TOGGLE, BuildHouseWindow::overbuild);
+
+				if (_settings_client.sound.click_beep) SndPlayFx(SND_15_BEEP);
+				this->SetDirty();
+				break;
+
 			default:
 				this->PickerWindow::OnClick(pt, widget, click_count);
 				break;
@@ -1768,6 +1777,8 @@ struct BuildHouseWindow : public PickerWindow {
 
 		this->SetWidgetLoweredState(WID_BH_PROTECT_OFF, !BuildHouseWindow::house_protected);
 		this->SetWidgetLoweredState(WID_BH_PROTECT_ON, BuildHouseWindow::house_protected);
+		this->SetWidgetLoweredState(WID_BH_OVERBUILD_TOGGLE, BuildHouseWindow::overbuild);
+
 
 		this->SetWidgetDisabledState(WID_BH_PROTECT_OFF, hasflag);
 		this->SetWidgetDisabledState(WID_BH_PROTECT_ON, hasflag);
@@ -1776,7 +1787,7 @@ struct BuildHouseWindow : public PickerWindow {
 	void OnPlaceObject([[maybe_unused]] Point pt, TileIndex tile) override
 	{
 		const HouseSpec *spec = HouseSpec::Get(HousePickerCallbacks::sel_type);
-		Command<CMD_PLACE_HOUSE>::Post(STR_ERROR_CAN_T_BUILD_HOUSE, CcPlaySound_CONSTRUCTION_OTHER, tile, spec->Index(), BuildHouseWindow::house_protected);
+		Command<CMD_PLACE_HOUSE>::Post(STR_ERROR_CAN_T_BUILD_HOUSE, CcPlaySound_CONSTRUCTION_OTHER, tile, spec->Index(), BuildHouseWindow::house_protected, BuildHouseWindow::overbuild);
 	}
 
 	const IntervalTimer<TimerWindow> view_refresh_interval = {std::chrono::milliseconds(2500), [this](auto) {
@@ -1811,9 +1822,9 @@ static constexpr NWidgetPart _nested_build_house_widgets[] = {
 						NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_BH_PROTECT_OFF), SetMinimalSize(60, 12), SetStringTip(STR_HOUSE_PICKER_PROTECT_OFF, STR_HOUSE_PICKER_PROTECT_TOOLTIP),
 						NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_BH_PROTECT_ON), SetMinimalSize(60, 12), SetStringTip(STR_HOUSE_PICKER_PROTECT_ON, STR_HOUSE_PICKER_PROTECT_TOOLTIP),
 					EndContainer(),
+					NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_BH_OVERBUILD_TOGGLE), SetMinimalSize(60, 12), SetStringTip(STR_HOUSE_PICKER_OVERBUILD, STR_HOUSE_PICKER_OVERBUILD_TOOLTIP),
 				EndContainer(),
 			EndContainer(),
-
 		EndContainer(),
 		NWidgetFunction(MakePickerTypeWidgets),
 	EndContainer(),

src/widgets/town_widget.h

@@ -79,6 +79,7 @@ enum BuildHouseWidgets : WidgetID {
 	WID_BH_INFO, ///< Information panel of selected house.
 	WID_BH_PROTECT_OFF, ///< Button to protect the next house built.
 	WID_BH_PROTECT_ON, ///< Button to not protect the next house built.
+	WID_BH_OVERBUILD_TOGGLE, ///< Button to toggle overbuilding existing houses.
 };
 
 #endif /* WIDGETS_TOWN_WIDGET_H */