Feature: Import town data from JSON file

src/fileio_type.h

@@ -18,6 +18,7 @@ enum AbstractFileType {
 	FT_SAVEGAME,  ///< old or new savegame
 	FT_SCENARIO,  ///< old or new scenario
 	FT_HEIGHTMAP, ///< heightmap file
+	FT_TOWN_DATA, ///< town data file
 
 	FT_INVALID = 7, ///< Invalid or unknown file type.
 	FT_NUMBITS = 3, ///< Number of bits required for storing a #AbstractFileType value.
@@ -34,6 +35,9 @@ enum DetailedFileType {
 	DFT_HEIGHTMAP_BMP, ///< BMP file.
 	DFT_HEIGHTMAP_PNG, ///< PNG file.
 
+	/* Town data files. */
+	DFT_TOWN_DATA_JSON,  ///< JSON file.
+
 	/* fios 'files' */
 	DFT_FIOS_DRIVE,  ///< A drive (letter) entry.
 	DFT_FIOS_PARENT, ///< A parent directory entry.
@@ -78,6 +82,7 @@ enum FiosType {
 	FIOS_TYPE_OLD_SCENARIO = MAKE_FIOS_TYPE(FT_SCENARIO, DFT_OLD_GAME_FILE),
 	FIOS_TYPE_PNG          = MAKE_FIOS_TYPE(FT_HEIGHTMAP, DFT_HEIGHTMAP_PNG),
 	FIOS_TYPE_BMP          = MAKE_FIOS_TYPE(FT_HEIGHTMAP, DFT_HEIGHTMAP_BMP),
+	FIOS_TYPE_JSON         = MAKE_FIOS_TYPE(FT_TOWN_DATA, DFT_TOWN_DATA_JSON),
 
 	FIOS_TYPE_INVALID = MAKE_FIOS_TYPE(FT_INVALID, DFT_INVALID),
 };

src/fios.cpp

@@ -84,6 +84,10 @@ void FileList::BuildFileList(AbstractFileType abstract_filetype, SaveLoadOperati
 			FiosGetHeightmapList(fop, show_dirs, *this);
 			break;
 
+		case FT_TOWN_DATA:
+			FiosGetTownDataList(fop, show_dirs, *this);
+			break;
+
 		default:
 			NOT_REACHED();
 	}
@@ -180,6 +184,7 @@ bool FiosBrowseTo(const FiosItem *item)
 		case FIOS_TYPE_OLD_SCENARIO:
 		case FIOS_TYPE_PNG:
 		case FIOS_TYPE_BMP:
+		case FIOS_TYPE_JSON:
 			return false;
 	}
 
@@ -554,6 +559,42 @@ void FiosGetHeightmapList(SaveLoadOperation fop, bool show_dirs, FileList &file_
 	FiosGetFileList(fop, show_dirs, &FiosGetHeightmapListCallback, subdir, file_list);
 }
 
+/**
+ * Callback for FiosGetTownDataList.
+ * @param fop Purpose of collecting the list.
+ * @param file Name of the file to check.
+ * @return a FIOS_TYPE_JSON type of the found file, FIOS_TYPE_INVALID if not a valid JSON file, and the title of the file (if any).
+ */
+static std::tuple<FiosType, std::string> FiosGetTownDataListCallback(SaveLoadOperation fop, const std::string &file, const std::string_view ext)
+{
+	if (fop == SLO_LOAD) {
+		if (StrEqualsIgnoreCase(ext, ".json")) {
+			return { FIOS_TYPE_JSON, GetFileTitle(file, SAVE_DIR) };
+		}
+	}
+
+	return { FIOS_TYPE_INVALID, {} };
+}
+
+/**
+ * Get a list of town data files.
+ * @param fop Purpose of collecting the list.
+ * @param show_dirs Whether to show directories.
+ * @param file_list Destination of the found files.
+ */
+void FiosGetTownDataList(SaveLoadOperation fop, bool show_dirs, FileList &file_list)
+{
+	static std::optional<std::string> fios_town_data_path;
+
+	if (!fios_town_data_path) fios_town_data_path = FioFindDirectory(HEIGHTMAP_DIR);
+
+	_fios_path = &(*fios_town_data_path);
+
+	std::string base_path = FioFindDirectory(HEIGHTMAP_DIR);
+	Subdirectory subdir = base_path == *_fios_path ? HEIGHTMAP_DIR : NO_DIRECTORY;
+	FiosGetFileList(fop, show_dirs, &FiosGetTownDataListCallback, subdir, file_list);
+}
+
 /**
  * Get the directory for screenshots.
  * @return path to screenshots

src/fios.h

@@ -107,6 +107,7 @@ void ShowSaveLoadDialog(AbstractFileType abstract_filetype, SaveLoadOperation fo
 void FiosGetSavegameList(SaveLoadOperation fop, bool show_dirs, FileList &file_list);
 void FiosGetScenarioList(SaveLoadOperation fop, bool show_dirs, FileList &file_list);
 void FiosGetHeightmapList(SaveLoadOperation fop, bool show_dirs, FileList &file_list);
+void FiosGetTownDataList(SaveLoadOperation fop, bool show_dirs, FileList &file_list);
 
 bool FiosBrowseTo(const FiosItem *item);
 

src/fios_gui.cpp

@@ -23,6 +23,7 @@
 #include "querystring_gui.h"
 #include "engine_func.h"
 #include "landscape_type.h"
+#include "genworld.h"
 #include "timer/timer_game_calendar.h"
 #include "core/geometry_func.hpp"
 #include "gamelog.h"
@@ -172,6 +173,48 @@ static constexpr NWidgetPart _nested_load_heightmap_dialog_widgets[] = {
 	EndContainer(),
 };
 
+/** Load town data */
+static constexpr NWidgetPart _nested_load_town_data_dialog_widgets[] = {
+	NWidget(NWID_HORIZONTAL),
+		NWidget(WWT_CLOSEBOX, COLOUR_GREY),
+		NWidget(WWT_CAPTION, COLOUR_GREY, WID_SL_CAPTION),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_GREY),
+	EndContainer(),
+	/* Current directory and free space */
+	NWidget(WWT_PANEL, COLOUR_GREY, WID_SL_BACKGROUND), SetFill(1, 0), SetResize(1, 0), EndContainer(),
+
+	/* Filter box with label */
+	NWidget(WWT_PANEL, COLOUR_GREY), SetFill(1, 1), SetResize(1, 1),
+		NWidget(NWID_HORIZONTAL), SetPadding(WidgetDimensions::unscaled.framerect.top, 0, WidgetDimensions::unscaled.framerect.bottom, 0),
+				SetPIP(WidgetDimensions::unscaled.frametext.left, WidgetDimensions::unscaled.frametext.right, 0),
+			NWidget(WWT_TEXT, COLOUR_GREY), SetFill(0, 1), SetDataTip(STR_SAVELOAD_FILTER_TITLE , STR_NULL),
+			NWidget(WWT_EDITBOX, COLOUR_GREY, WID_SL_FILTER), SetFill(1, 0), SetResize(1, 0), SetDataTip(STR_LIST_FILTER_OSKTITLE, STR_LIST_FILTER_TOOLTIP),
+		EndContainer(),
+	EndContainer(),
+	/* Sort Buttons */
+	NWidget(NWID_HORIZONTAL),
+		NWidget(NWID_HORIZONTAL, NC_EQUALSIZE),
+			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_SL_SORT_BYNAME), SetDataTip(STR_SORT_BY_CAPTION_NAME, STR_TOOLTIP_SORT_ORDER), SetFill(1, 0), SetResize(1, 0),
+			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_SL_SORT_BYDATE), SetDataTip(STR_SORT_BY_CAPTION_DATE, STR_TOOLTIP_SORT_ORDER), SetFill(1, 0), SetResize(1, 0),
+		EndContainer(),
+		NWidget(WWT_PUSHIMGBTN, COLOUR_GREY, WID_SL_HOME_BUTTON), SetAspect(1), SetDataTip(SPR_HOUSE_ICON, STR_SAVELOAD_HOME_BUTTON),
+	EndContainer(),
+	/* Files */
+	NWidget(NWID_HORIZONTAL),
+		NWidget(WWT_PANEL, COLOUR_GREY, WID_SL_FILE_BACKGROUND),
+			NWidget(WWT_INSET, COLOUR_GREY, WID_SL_DRIVES_DIRECTORIES_LIST), SetFill(1, 1), SetPadding(2, 2, 2, 2),
+					SetDataTip(0x0, STR_SAVELOAD_LIST_TOOLTIP), SetResize(1, 10), SetScrollbar(WID_SL_SCROLLBAR), EndContainer(),
+		EndContainer(),
+		NWidget(NWID_VSCROLLBAR, COLOUR_GREY, WID_SL_SCROLLBAR),
+	EndContainer(),
+	/* Load button */
+	NWidget(NWID_HORIZONTAL, NC_EQUALSIZE),
+		NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_SL_LOAD_BUTTON), SetResize(1, 0), SetFill(1, 0),
+				SetDataTip(STR_SAVELOAD_LOAD_BUTTON, STR_SAVELOAD_LOAD_TOWN_DATA_TOOLTIP),
+		NWidget(WWT_RESIZEBOX, COLOUR_GREY),
+	EndContainer(),
+};
+
 /** Save game/scenario */
 static constexpr NWidgetPart _nested_save_dialog_widgets[] = {
 	NWidget(NWID_HORIZONTAL),
@@ -242,6 +285,7 @@ static const TextColour _fios_colours[] = {
 	TC_ORANGE,       // DFT_GAME_FILE
 	TC_YELLOW,       // DFT_HEIGHTMAP_BMP
 	TC_ORANGE,       // DFT_HEIGHTMAP_PNG
+	TC_LIGHT_BROWN,  // DFT_TOWN_DATA_JSON
 	TC_LIGHT_BLUE,   // DFT_FIOS_DRIVE
 	TC_DARK_GREEN,   // DFT_FIOS_PARENT
 	TC_DARK_GREEN,   // DFT_FIOS_DIR
@@ -330,6 +374,7 @@ public:
 					break;
 
 				default:
+					/* It's not currently possible to save town data. */
 					NOT_REACHED();
 			}
 		}
@@ -356,6 +401,10 @@ public:
 				caption_string = (this->fop == SLO_SAVE) ? STR_SAVELOAD_SAVE_HEIGHTMAP : STR_SAVELOAD_LOAD_HEIGHTMAP;
 				break;
 
+			case FT_TOWN_DATA:
+				caption_string = STR_SAVELOAD_LOAD_TOWN_DATA; // It's not currently possible to save town data.
+				break;
+
 			default:
 				NOT_REACHED();
 		}
@@ -391,6 +440,7 @@ public:
 				break;
 
 			case FT_HEIGHTMAP:
+			case FT_TOWN_DATA:
 				o_dir.name = FioFindDirectory(HEIGHTMAP_DIR);
 				break;
 
@@ -634,6 +684,9 @@ public:
 				if (this->abstract_filetype == FT_HEIGHTMAP) {
 					this->Close();
 					ShowHeightmapLoad();
+				} else if (this->abstract_filetype == FT_TOWN_DATA) {
+					this->Close();
+					LoadTownData();
 				} else if (!_load_check_data.HasNewGrfs() || _load_check_data.grf_compatibility != GLC_NOT_FOUND || _settings_client.gui.UserIsAllowedToChangeNewGRFs()) {
 					_switch_mode = (_game_mode == GM_EDITOR) ? SM_LOAD_SCENARIO : SM_LOAD_GAME;
 					ClearErrorMessages();
@@ -689,7 +742,7 @@ public:
 				} else if (!_load_check_data.HasErrors()) {
 					this->selected = file;
 					if (this->fop == SLO_LOAD) {
-						if (this->abstract_filetype == FT_SAVEGAME || this->abstract_filetype == FT_SCENARIO) {
+						if (this->abstract_filetype == FT_SAVEGAME || this->abstract_filetype == FT_SCENARIO || this->abstract_filetype == FT_TOWN_DATA) {
 							this->OnClick(pt, WID_SL_LOAD_BUTTON, 1);
 						} else {
 							assert(this->abstract_filetype == FT_HEIGHTMAP);
@@ -856,6 +909,7 @@ public:
 
 				switch (this->abstract_filetype) {
 					case FT_HEIGHTMAP:
+					case FT_TOWN_DATA:
 						this->SetWidgetDisabledState(WID_SL_LOAD_BUTTON, this->selected == nullptr || _load_check_data.HasErrors());
 						break;
 
@@ -908,6 +962,14 @@ static WindowDesc _load_heightmap_dialog_desc(
 	_nested_load_heightmap_dialog_widgets
 );
 
+/** Load town data */
+static WindowDesc _load_town_data_dialog_desc(
+	WDP_CENTER, "load_town_data", 257, 320,
+	WC_SAVELOAD, WC_NONE,
+	0,
+	_nested_load_town_data_dialog_widgets
+);
+
 /** Save game/scenario */
 static WindowDesc _save_dialog_desc(
 	WDP_CENTER, "save_game", 500, 294,
@@ -929,6 +991,17 @@ void ShowSaveLoadDialog(AbstractFileType abstract_filetype, SaveLoadOperation fo
 		new SaveLoadWindow(_save_dialog_desc, abstract_filetype, fop);
 	} else {
 		/* Dialogue for loading a file. */
-		new SaveLoadWindow((abstract_filetype == FT_HEIGHTMAP) ? _load_heightmap_dialog_desc : _load_dialog_desc, abstract_filetype, fop);
+		switch (abstract_filetype) {
+			case FT_HEIGHTMAP:
+				new SaveLoadWindow(_load_heightmap_dialog_desc, abstract_filetype, fop);
+				break;
+
+			case FT_TOWN_DATA:
+				new SaveLoadWindow(_load_town_data_dialog_desc, abstract_filetype, fop);
+				break;
+
+			default:
+				new SaveLoadWindow(_load_dialog_desc, abstract_filetype, fop);
+		}
 	}
 }

src/genworld.cpp

@@ -10,6 +10,10 @@
 #include "stdafx.h"
 #include "landscape.h"
 #include "company_func.h"
+#include "town_cmd.h"
+#include "signs_cmd.h"
+#include "3rdparty/nlohmann/json.hpp"
+#include "strings_func.h"
 #include "genworld.h"
 #include "gfxinit.h"
 #include "window_func.h"
@@ -337,3 +341,178 @@ void GenerateWorld(GenWorldMode mode, uint size_x, uint size_y, bool reset_setti
 
 	_GenerateWorld();
 }
+
+/** Town data imported from JSON files and used to place towns. */
+struct ExternalTownData {
+	TownID town_id; ///< The TownID of the town in OpenTTD. Not imported, but set during the founding proceess and stored here for convenience.
+	std::string name; ///< The name of the town.
+	uint population; ///< The target population of the town when created in OpenTTD. If input is blank, defaults to 0.
+	bool is_city; ///< Should it be created as a city in OpenTTD? If input is blank, defaults to false.
+	float x_proportion; ///< The X coordinate of the town, as a proportion 0..1 of the maximum X coordinate.
+	float y_proportion; ///< The Y coordinate of the town, as a proportion 0..1 of the maximum Y coordinate.
+};
+
+/**
+ * Helper for CircularTileSearch to found a town on or near a given tile.
+ * @param tile The tile to try founding the town upon.
+ * @param user_data The ExternalTownData to attempt to found.
+ * @return True if the town was founded successfully.
+ */
+static bool TryFoundTownNearby(TileIndex tile, void *user_data)
+{
+	ExternalTownData &town = *static_cast<ExternalTownData *>(user_data);
+	std::tuple<CommandCost, Money, TownID> result = Command<CMD_FOUND_TOWN>::Do(DC_EXEC, tile, TSZ_SMALL, town.is_city, _settings_game.economy.town_layout, false, 0, town.name);
+
+	TownID id = std::get<TownID>(result);
+
+	/* Check if the command failed. */
+	if (id == INVALID_TOWN) return false;
+
+	/* The command succeeded, send the ID back through user_data. */
+	town.town_id = id;
+	return true;
+}
+
+/**
+ * Load town data from _file_to_saveload, place towns at the appropriate locations, and expand them to their target populations.
+ */
+void LoadTownData()
+{
+	/* Load the JSON file as a string initially. We'll parse it soon. */
+	size_t filesize;
+	FILE *f = FioFOpenFile(_file_to_saveload.name, "rb", HEIGHTMAP_DIR, &filesize);
+
+	if (f == nullptr) {
+		ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+		return;
+	}
+
+	std::string text(filesize, '\0');
+	size_t len = fread(text.data(), filesize, 1, f);
+	FioFCloseFile(f);
+	if (len != 1) {
+		ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+		return;
+	}
+
+	/* Now parse the JSON. */
+	nlohmann::json town_data;
+	try {
+		town_data = nlohmann::json::parse(text);
+	} catch (nlohmann::json::exception &) {
+		ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+		return;
+	}
+
+	/* Check for JSON formatting errors with the array of towns. */
+	if (!town_data.is_array()) {
+		ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+		return;
+	}
+
+	std::vector<std::pair<Town *, uint> > towns;
+	uint failed_towns = 0;
+
+	/* Iterate through towns and attempt to found them. */
+	for (auto &feature : town_data) {
+		ExternalTownData town;
+
+		/* Ensure JSON is formatted properly. */
+		if (!feature.is_object()) {
+			ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+			return;
+		}
+
+		/* Check to ensure all fields exist and are of the correct type.
+		 * If the town name is formatted wrong, all we can do is give a general warning. */
+		if (!feature.contains("name") || !feature.at("name").is_string()) {
+			ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY, WL_ERROR);
+			return;
+		}
+
+		/* If other fields are formatted wrong, we can actually inform the player which town is the problem. */
+		if (!feature.contains("population") || !feature.at("population").is_number() ||
+				!feature.contains("city") || !feature.at("city").is_boolean() ||
+				!feature.contains("x") || !feature.at("x").is_number() ||
+				!feature.contains("y") || !feature.at("y").is_number()) {
+			feature.at("name").get_to(town.name);
+			SetDParamStr(0, town.name);
+			ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_TOWN_FORMATTED_INCORRECTLY, WL_ERROR);
+			return;
+		}
+
+		/* Set town properties. */
+		feature.at("name").get_to(town.name);
+		feature.at("population").get_to(town.population);
+		feature.at("city").get_to(town.is_city);
+
+		/* Set town coordinates. */
+		feature.at("x").get_to(town.x_proportion);
+		feature.at("y").get_to(town.y_proportion);
+
+		/* Check for improper coordinates and warn the player. */
+		if (town.x_proportion <= 0.0f || town.y_proportion <= 0.0f || town.x_proportion >= 1.0f || town.y_proportion >= 1.0f) {
+			SetDParamStr(0, town.name);
+			ShowErrorMessage(STR_TOWN_DATA_ERROR_LOAD_FAILED, STR_TOWN_DATA_ERROR_BAD_COORDINATE, WL_ERROR);
+			return;
+		}
+
+		/* Find the target tile for the town. */
+		TileIndex tile;
+		switch (_settings_game.game_creation.heightmap_rotation) {
+			case HM_CLOCKWISE:
+				/* Tile coordinates align with what we expect. */
+				tile = TileXY(town.x_proportion * Map::MaxX(), town.y_proportion * Map::MaxY());
+				break;
+			case HM_COUNTER_CLOCKWISE:
+				/* Tile coordinates are rotated and must be adjusted. */
+				tile = TileXY((1 - town.y_proportion * Map::MaxX()), town.x_proportion * Map::MaxY());
+				break;
+			default: NOT_REACHED();
+		}
+
+		/* Try founding on the target tile, and if that doesn't work, find the nearest suitable tile up to 16 tiles away.
+		 * The target might be on water, blocked somehow, or on a steep slope that can't be terraformed by the founding command. */
+		TileIndex search_tile = tile;
+		bool success = CircularTileSearch(&search_tile, 16, 0, 0, TryFoundTownNearby, &town);
+
+		/* If we still fail to found the town, we'll create a sign at the intended location and tell the player how many towns we failed to create in an error message.
+		 * This allows the player to diagnose a heightmap misalignment, if towns end up in the sea, or place towns manually, if in rough terrain. */
+		if (!success) {
+			Command<CMD_PLACE_SIGN>::Post(tile, town.name);
+			failed_towns++;
+			continue;
+		}
+
+		towns.emplace_back(std::make_pair(Town::Get(town.town_id), town.population));
+	}
+
+	/* If we couldn't found a town (or multiple), display a message to the player with the number of failed towns. */
+	if (failed_towns > 0) {
+		SetDParam(0, failed_towns);
+		ShowErrorMessage(STR_TOWN_DATA_ERROR_FAILED_TO_FOUND_TOWN, INVALID_STRING_ID, WL_WARNING);
+	}
+
+	/* Now that we've created the towns, let's grow them to their target populations. */
+	for (const auto &item : towns) {
+		Town *t = item.first;
+		uint population = item.second;
+
+		/* Grid towns can grow almost forever, but the town growth algorithm gets less and less efficient as it wanders roads randomly,
+		 * so we set an arbitrary limit. With a flat map and a 3x3 grid layout this results in about 4900 houses, or 2800 houses with "Better roads." */
+		int try_limit = 1000;
+
+		/* If a town repeatedly fails to grow, continuing to try only wastes time. */
+		int fail_limit = 10;
+
+		/* Grow by a constant number of houses each time, instead of growth based on current town size.
+		 * We want our try limit to apply in a predictable way, no matter the road layout and other geography. */
+		const int HOUSES_TO_GROW = 10;
+
+		do {
+			uint before = t->cache.num_houses;
+			Command<CMD_EXPAND_TOWN>::Post(t->index, HOUSES_TO_GROW);
+			if (t->cache.num_houses <= before) fail_limit--;
+		} while (fail_limit > 0 && try_limit-- > 0 && t->cache.population < population);
+	}
+}

src/genworld.h

@@ -89,6 +89,7 @@ void GenerateWorld(GenWorldMode mode, uint size_x, uint size_y, bool reset_setti
 void AbortGeneratingWorld();
 bool IsGeneratingWorldAborted();
 void HandleGeneratingWorldAbortion();
+void LoadTownData();
 
 /* genworld_gui.cpp */
 void SetNewLandscapeType(uint8_t landscape);

src/lang/english.txt

@@ -3019,6 +3019,8 @@ STR_FOUND_TOWN_RANDOM_TOWN_BUTTON                               :{BLACK}Random T
 STR_FOUND_TOWN_RANDOM_TOWN_TOOLTIP                              :{BLACK}Found town in random location
 STR_FOUND_TOWN_MANY_RANDOM_TOWNS                                :{BLACK}Many random towns
 STR_FOUND_TOWN_RANDOM_TOWNS_TOOLTIP                             :{BLACK}Cover the map with randomly placed towns
+STR_FOUND_TOWN_LOAD_FROM_FILE                                   :{BLACK}Load from file
+STR_FOUND_TOWN_LOAD_FROM_FILE_TOOLTIP                           :{BLACK}Import town data from a JSON file
 STR_FOUND_TOWN_EXPAND_ALL_TOWNS                                 :{BLACK}Expand all towns
 STR_FOUND_TOWN_EXPAND_ALL_TOWNS_TOOLTIP                         :{BLACK}Make all towns grow slightly
 
@@ -3271,6 +3273,7 @@ STR_SAVELOAD_SAVE_SCENARIO                                      :{WHITE}Save Sce
 STR_SAVELOAD_LOAD_SCENARIO                                      :{WHITE}Load Scenario
 STR_SAVELOAD_LOAD_HEIGHTMAP                                     :{WHITE}Load Heightmap
 STR_SAVELOAD_SAVE_HEIGHTMAP                                     :{WHITE}Save Heightmap
+STR_SAVELOAD_LOAD_TOWN_DATA                                     :{WHITE}Load Town Data
 STR_SAVELOAD_HOME_BUTTON                                        :{BLACK}Click here to jump to the current default save/load directory
 STR_SAVELOAD_BYTES_FREE                                         :{BLACK}{BYTES} free
 STR_SAVELOAD_LIST_TOOLTIP                                       :{BLACK}List of drives, directories and saved-game files
@@ -3282,6 +3285,7 @@ STR_SAVELOAD_SAVE_TOOLTIP                                       :{BLACK}Save the
 STR_SAVELOAD_LOAD_BUTTON                                        :{BLACK}Load
 STR_SAVELOAD_LOAD_TOOLTIP                                       :{BLACK}Load the selected game
 STR_SAVELOAD_LOAD_HEIGHTMAP_TOOLTIP                             :{BLACK}Load the selected heightmap
+STR_SAVELOAD_LOAD_TOWN_DATA_TOOLTIP                             :{BLACK}Load the selected town data
 STR_SAVELOAD_DETAIL_CAPTION                                     :{BLACK}Game Details
 STR_SAVELOAD_DETAIL_NOT_AVAILABLE                               :{BLACK}No information available
 STR_SAVELOAD_DETAIL_COMPANY_INDEX                               :{SILVER}{COMMA}: {WHITE}{STRING1}
@@ -3415,6 +3419,13 @@ STR_GENERATION_PREPARING_TILELOOP                               :{BLACK}Running
 STR_GENERATION_PREPARING_SCRIPT                                 :{BLACK}Running script
 STR_GENERATION_PREPARING_GAME                                   :{BLACK}Preparing game
 
+STR_TOWN_DATA_ERROR_LOAD_FAILED                                 :{WHITE}Town data load failed
+STR_TOWN_DATA_ERROR_JSON_FORMATTED_INCORRECTLY                  :{WHITE}JSON file formatted incorrectly
+STR_TOWN_DATA_ERROR_TOWN_FORMATTED_INCORRECTLY                  :{WHITE}{RAW_STRING} data formatted incorrectly
+STR_TOWN_DATA_ERROR_BAD_COORDINATE                              :{WHITE}{RAW_STRING} coordinates formatted incorrectly, must be 0..1 as a percentage of the total heightmap dimension
+
+STR_TOWN_DATA_ERROR_FAILED_TO_FOUND_TOWN                        :{WHITE}Could not find valid location to found {NUM} town{P "" s}. Created {P "a " ""}sign{P "" s} at the intended location{P "" s} instead
+
 # NewGRF settings
 STR_NEWGRF_SETTINGS_CAPTION                                     :{WHITE}NewGRF Settings
 STR_NEWGRF_SETTINGS_INFO_TITLE                                  :{WHITE}Detailed NewGRF information

src/town_gui.cpp

@@ -33,6 +33,7 @@
 #include "core/backup_type.hpp"
 #include "core/geometry_func.hpp"
 #include "genworld.h"
+#include "fios.h"
 #include "stringfilter_type.h"
 #include "dropdown_func.h"
 #include "town_kdtree.h"
@@ -1108,6 +1109,7 @@ static constexpr NWidgetPart _nested_found_town_widgets[] = {
 			NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_TF_NEW_TOWN), SetDataTip(STR_FOUND_TOWN_NEW_TOWN_BUTTON, STR_FOUND_TOWN_NEW_TOWN_TOOLTIP), SetFill(1, 0),
 			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_TF_RANDOM_TOWN), SetDataTip(STR_FOUND_TOWN_RANDOM_TOWN_BUTTON, STR_FOUND_TOWN_RANDOM_TOWN_TOOLTIP), SetFill(1, 0),
 			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_TF_MANY_RANDOM_TOWNS), SetDataTip(STR_FOUND_TOWN_MANY_RANDOM_TOWNS, STR_FOUND_TOWN_RANDOM_TOWNS_TOOLTIP), SetFill(1, 0),
+			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_TF_LOAD_FROM_FILE), SetDataTip(STR_FOUND_TOWN_LOAD_FROM_FILE, STR_FOUND_TOWN_LOAD_FROM_FILE_TOOLTIP), SetFill(1, 0),
 			NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_TF_EXPAND_ALL_TOWNS), SetDataTip(STR_FOUND_TOWN_EXPAND_ALL_TOWNS, STR_FOUND_TOWN_EXPAND_ALL_TOWNS_TOOLTIP), SetFill(1, 0),
 
 			/* Town name selection. */
@@ -1188,7 +1190,7 @@ public:
 	void UpdateButtons(bool check_availability)
 	{
 		if (check_availability && _game_mode != GM_EDITOR) {
-			this->SetWidgetsDisabledState(true, WID_TF_RANDOM_TOWN, WID_TF_MANY_RANDOM_TOWNS, WID_TF_EXPAND_ALL_TOWNS, WID_TF_SIZE_LARGE);
+			this->SetWidgetsDisabledState(true, WID_TF_RANDOM_TOWN, WID_TF_MANY_RANDOM_TOWNS, WID_TF_LOAD_FROM_FILE, WID_TF_EXPAND_ALL_TOWNS, WID_TF_SIZE_LARGE);
 			this->SetWidgetsDisabledState(_settings_game.economy.found_town != TF_CUSTOM_LAYOUT,
 					WID_TF_LAYOUT_ORIGINAL, WID_TF_LAYOUT_BETTER, WID_TF_LAYOUT_GRID2, WID_TF_LAYOUT_GRID3, WID_TF_LAYOUT_RANDOM);
 			if (_settings_game.economy.found_town != TF_CUSTOM_LAYOUT) town_layout = _settings_game.economy.town_layout;
@@ -1254,6 +1256,10 @@ public:
 				break;
 			}
 
+			case WID_TF_LOAD_FROM_FILE:
+				ShowSaveLoadDialog(FT_TOWN_DATA, SLO_LOAD);
+				break;
+
 			case WID_TF_EXPAND_ALL_TOWNS:
 				for (Town *t : Town::Iterate()) {
 					Command<CMD_EXPAND_TOWN>::Do(DC_EXEC, t->index, 0);

src/widgets/town_widget.h

@@ -50,6 +50,7 @@ enum TownFoundingWidgets : WidgetID {
 	WID_TF_NEW_TOWN,          ///< Create a new town.
 	WID_TF_RANDOM_TOWN,       ///< Randomly place a town.
 	WID_TF_MANY_RANDOM_TOWNS, ///< Randomly place many towns.
+	WID_TF_LOAD_FROM_FILE,    ///< Load town data from file.
 	WID_TF_EXPAND_ALL_TOWNS,  ///< Make all towns grow slightly.
 	WID_TF_TOWN_NAME_EDITBOX, ///< Editor for the town name.
 	WID_TF_TOWN_NAME_RANDOM,  ///< Generate a random town name.