Feature: auto-detect map height limit based on generated map

This opens up the true power of the TGP terrain generator, as it
is no longer constrainted by an arbitrary low map height limit,
especially for extreme terrain types.

In other words: on a 1kx1k map with "Alpinist" terrain type, the
map is now really hilly with default settings.

People can still manually limit the map height if they so wish,
and after the terrain generation the limit is stored in the
savegame as if the user set it.

Cheats still allow you to change this value.

8 files changed, 52 insertions, 10 deletions

diff --git a/src/genworld.cpp b/src/genworld.cpp
index 0bd64f896..d357a1516 100644
--- a/src/genworld.cpp
+++ b/src/genworld.cpp
@@ -33,6 +33,7 @@
 #include "game/game_instance.hpp"
 #include "string_func.h"
 #include "thread.h"
+#include "tgp.h"
 
 #include "safeguards.h"
 
@@ -285,6 +286,20 @@ void GenerateWorld(GenWorldMode mode, uint size_x, uint size_y, bool reset_setti
 	InitializeGame(_gw.size_x, _gw.size_y, true, reset_settings);
 	PrepareGenerateWorldProgress();
 
+	if (_settings_game.construction.map_height_limit == 0) {
+		uint estimated_height = 0;
+
+		if (_gw.mode == GWM_EMPTY && _game_mode != GM_MENU) {
+			estimated_height = _settings_game.game_creation.se_flat_world_height;
+		} else if (_settings_game.game_creation.land_generator == LG_TERRAGENESIS) {
+			estimated_height = GetEstimationTGPMapHeight();
+		} else {
+			estimated_height = 0;
+		}
+
+		_settings_game.construction.map_height_limit = std::max(MAP_HEIGHT_LIMIT_AUTO_MINIMUM, std::min(MAX_MAP_HEIGHT_LIMIT, estimated_height + MAP_HEIGHT_LIMIT_AUTO_CEILING_ROOM));
+	}
+
 	/* Load the right landscape stuff, and the NewGRFs! */
 	GfxLoadSprites();
 	LoadStringWidthTable();
diff --git a/src/genworld.h b/src/genworld.h
index e780ed169..71dae3f36 100644
--- a/src/genworld.h
+++ b/src/genworld.h
@@ -46,6 +46,9 @@ static const uint CUSTOM_SEA_LEVEL_NUMBER_DIFFICULTY = 4; ///< Value for custom
 static const uint CUSTOM_SEA_LEVEL_MIN_PERCENTAGE = 1;    ///< Minimum percentage a user can specify for custom sea level.
 static const uint CUSTOM_SEA_LEVEL_MAX_PERCENTAGE = 90;   ///< Maximum percentage a user can specify for custom sea level.
 
+static const uint MAP_HEIGHT_LIMIT_AUTO_MINIMUM = 30; ///< When map height limit is auto, make this the lowest possible map height limit.
+static const uint MAP_HEIGHT_LIMIT_AUTO_CEILING_ROOM = 15; ///< When map height limit is auto, the map height limit will be the higest peak plus this value.
+
 typedef void GWDoneProc();  ///< Procedure called when the genworld process finishes
 typedef void GWAbortProc(); ///< Called when genworld is aborted
 
diff --git a/src/genworld_gui.cpp b/src/genworld_gui.cpp
index 0ca4543f2..5e1fac685 100644
--- a/src/genworld_gui.cpp
+++ b/src/genworld_gui.cpp
@@ -46,6 +46,15 @@ enum GenerateLandscapeWindowMode {
 };
 
 /**
+ * Get the map height limit, or if set to "auto", the absolute limit.
+ */
+static uint GetMapHeightLimit()
+{
+	if (_settings_newgame.construction.map_height_limit == 0) return MAX_MAP_HEIGHT_LIMIT;
+	return _settings_newgame.construction.map_height_limit;
+}
+
+/**
  * Changes landscape type and sets genworld window dirty
  * @param landscape new landscape type
  */
@@ -974,7 +983,7 @@ struct CreateScenarioWindow : public Window
 		this->SetWidgetDisabledState(WID_CS_START_DATE_DOWN,       _settings_newgame.game_creation.starting_year <= MIN_YEAR);
 		this->SetWidgetDisabledState(WID_CS_START_DATE_UP,         _settings_newgame.game_creation.starting_year >= MAX_YEAR);
 		this->SetWidgetDisabledState(WID_CS_FLAT_LAND_HEIGHT_DOWN, _settings_newgame.game_creation.se_flat_world_height <= 0);
-		this->SetWidgetDisabledState(WID_CS_FLAT_LAND_HEIGHT_UP,   _settings_newgame.game_creation.se_flat_world_height >= MAX_TILE_HEIGHT);
+		this->SetWidgetDisabledState(WID_CS_FLAT_LAND_HEIGHT_UP,   _settings_newgame.game_creation.se_flat_world_height >= GetMapHeightLimit());
 
 		this->SetWidgetLoweredState(WID_CS_TEMPERATE, _settings_newgame.game_creation.landscape == LT_TEMPERATE);
 		this->SetWidgetLoweredState(WID_CS_ARCTIC,    _settings_newgame.game_creation.landscape == LT_ARCTIC);
@@ -1062,7 +1071,7 @@ struct CreateScenarioWindow : public Window
 					this->HandleButtonClick(widget);
 					this->SetDirty();
 
-					_settings_newgame.game_creation.se_flat_world_height = Clamp(_settings_newgame.game_creation.se_flat_world_height + widget - WID_CS_FLAT_LAND_HEIGHT_TEXT, 0, _settings_game.construction.map_height_limit);
+					_settings_newgame.game_creation.se_flat_world_height = Clamp(_settings_newgame.game_creation.se_flat_world_height + widget - WID_CS_FLAT_LAND_HEIGHT_TEXT, 0, GetMapHeightLimit());
 				}
 				_left_button_clicked = false;
 				break;
@@ -1108,7 +1117,7 @@ struct CreateScenarioWindow : public Window
 
 				case WID_CS_FLAT_LAND_HEIGHT_TEXT:
 					this->SetWidgetDirty(WID_CS_FLAT_LAND_HEIGHT_TEXT);
-					_settings_newgame.game_creation.se_flat_world_height = Clamp(value, 0, _settings_game.construction.map_height_limit);
+					_settings_newgame.game_creation.se_flat_world_height = Clamp(value, 0, GetMapHeightLimit());
 					break;
 			}
 
diff --git a/src/lang/english.txt b/src/lang/english.txt
index bc38876e4..94dbba787 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -1206,7 +1206,9 @@ STR_CONFIG_SETTING_CITY_APPROVAL                                :Town council's
 STR_CONFIG_SETTING_CITY_APPROVAL_HELPTEXT                       :Choose how much noise and environmental damage by companies affect their town rating and further construction actions in their area
 
 STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT                             :Map height limit: {STRING2}
-STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_HELPTEXT                    :Set the maximum allowed height of the map; neither the terrain generator nor you can build higher than this limit
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_HELPTEXT                    :Set the maximum allowed height of the map; neither the terrain generator nor you can build higher than this limit. On (auto) it will pick a good value after terrain generation
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_VALUE                       :{NUM}
+STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_AUTO                        :(auto)
 STR_CONFIG_SETTING_TOO_HIGH_MOUNTAIN                            :{WHITE}You can't set the map height limit to this value. At least one mountain on the map is higher
 STR_CONFIG_SETTING_AUTOSLOPE                                    :Allow landscaping under buildings, tracks, etc.: {STRING2}
 STR_CONFIG_SETTING_AUTOSLOPE_HELPTEXT                           :Allow landscaping under buildings and tracks without removing them
diff --git a/src/table/settings.ini b/src/table/settings.ini
index 67403a3bf..ae6a40e9f 100644
--- a/src/table/settings.ini
+++ b/src/table/settings.ini
@@ -394,16 +394,16 @@ base     = GameSettings
 var      = construction.map_height_limit
 type     = SLE_UINT8
 from     = SLV_194
-guiflags = SGF_NEWGAME_ONLY | SGF_SCENEDIT_TOO
-def      = DEF_MAP_HEIGHT_LIMIT
+guiflags = SGF_NEWGAME_ONLY | SGF_SCENEDIT_TOO | SGF_0ISDISABLED
+def      = 0
 min      = MIN_MAP_HEIGHT_LIMIT
 max      = MAX_MAP_HEIGHT_LIMIT
 interval = 1
 str      = STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT
 strhelp  = STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_HELPTEXT
-strval   = STR_JUST_INT
+strval   = STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_VALUE
 proc     = ChangeMaxHeightLevel
-cat      = SC_BASIC
+cat      = SC_ADVANCED
 
 [SDT_BOOL]
 base     = GameSettings
diff --git a/src/tgp.cpp b/src/tgp.cpp
index 92e714d9b..3ced2a1b0 100644
--- a/src/tgp.cpp
+++ b/src/tgp.cpp
@@ -237,7 +237,20 @@ static height_t TGPGetMaxHeight()
 	int map_size_bucket = std::min(MapLogX(), MapLogY()) - MIN_MAP_SIZE_BITS;
 	int max_height_from_table = max_height[_settings_game.difficulty.terrain_type][map_size_bucket];
 
-	return I2H(std::min<uint>(max_height_from_table, _settings_game.construction.map_height_limit));
+	/* If there is a manual map height limit, clamp to it. */
+	if (_settings_game.construction.map_height_limit != 0) {
+		max_height_from_table = std::min<uint>(max_height_from_table, _settings_game.construction.map_height_limit);
+	}
+
+	return I2H(max_height_from_table);
+}
+
+/**
+ * Get an overestimation of the highest peak TGP wants to generate.
+ */
+uint GetEstimationTGPMapHeight()
+{
+	return H2I(TGPGetMaxHeight());
 }
 
 /**
diff --git a/src/tgp.h b/src/tgp.h
index 8d8d97489..e773c6ff2 100644
--- a/src/tgp.h
+++ b/src/tgp.h
@@ -11,5 +11,6 @@
 #define TGP_H
 
 void GenerateTerrainPerlin();
+uint GetEstimationTGPMapHeight();
 
 #endif /* TGP_H */
diff --git a/src/tile_type.h b/src/tile_type.h
index ad3d1b563..17b4ad206 100644
--- a/src/tile_type.h
+++ b/src/tile_type.h
@@ -22,7 +22,6 @@ static const int MAX_VEHICLE_PIXEL_Y  = 96;                    ///< Maximum heig
 static const uint MAX_TILE_HEIGHT     = 255;                   ///< Maximum allowed tile height
 
 static const uint MIN_MAP_HEIGHT_LIMIT = 15;                   ///< Lower bound of maximum allowed heightlevel (in the construction settings)
-static const uint DEF_MAP_HEIGHT_LIMIT = 30;                   ///< Default maximum allowed heightlevel (in the construction settings)
 static const uint MAX_MAP_HEIGHT_LIMIT = MAX_TILE_HEIGHT;      ///< Upper bound of maximum allowed heightlevel (in the construction settings)
 
 static const uint MIN_SNOWLINE_HEIGHT = 2;                     ///< Minimum snowline height