* @return the cost of this operation or an error

 * @see _settings

 */

CommandCost CmdChangeSetting(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)

{

	const SettingDesc *sd = GetSettingDescription(p1);

	if (sd == NULL) return CMD_ERROR;

	if (!SlIsObjectCurrentlyValid(sd->save.version_from, sd->save.version_to)) return CMD_ERROR;

	if ((sd->desc.flags & SGF_NETWORK_ONLY) && !_networking && _game_mode != GM_MENU) return CMD_ERROR;

	if ((sd->desc.flags & SGF_NO_NETWORK) && _networking) return CMD_ERROR;

	if (flags & DC_EXEC) {

		GameSettings *s = (_game_mode == GM_MENU) ? &_settings_newgame : &_settings_game;

		void *var = GetVariableAddress(s, &sd->save);

		int32 oldval = (int32)ReadValue(var, sd->save.conv);

		int32 newval = (int32)p2;

		Write_ValidateSetting(var, sd, newval);

		newval = (int32)ReadValue(var, sd->save.conv);

		if (oldval == newval) return CommandCost();

	/** The number of widgets per difficulty setting */

	static const uint WIDGETS_PER_DIFFICULTY = 3;

	GameDifficultyWindow(const WindowDesc *desc) : Window()

	{

		this->InitNested(desc);

		/* Copy current settings (ingame or in intro) to temporary holding place

		 * change that when setting stuff, copy back on clicking 'OK' */

		this->opt_mod_temp = (_game_mode == GM_MENU) ? _settings_newgame : _settings_game;

		/* Setup disabled buttons when creating window

		 * disable all other difficulty buttons during gameplay except for 'custom' */

			GDW_LVL_EASY,

			GDW_LVL_MEDIUM,

			GDW_LVL_HARD,

			GDW_LVL_CUSTOM,

			WIDGET_LIST_END);

		this->SetWidgetDisabledState(GDW_HIGHSCORE, _game_mode == GM_EDITOR || _networking); // highscore chart in multiplayer

		this->SetWidgetDisabledState(GDW_ACCEPT, _networking && !_network_server); // Save-button in multiplayer (and if client)

		this->LowerWidget(GDW_LVL_EASY + this->opt_mod_temp.difficulty.diff_level);

		this->OnInvalidateData();

	}

	virtual void SetStringParameters(int widget) const

	{

		if (widget >= GDW_OPTIONS_START) {

			widget -= GDW_OPTIONS_START;

			if ((widget % 3) == 2) return;

			/* Don't allow clients to make any changes */

			if (_networking && !_network_server) return;

			uint i;

			const SettingDesc *sd = GetSettingFromName("difficulty.max_no_competitors", &i) + (widget / 3);

			const SettingDescBase *sdb = &sd->desc;

			int32 val = (int32)ReadValue(GetVariableAddress(&this->opt_mod_temp, &sd->save), sd->save.conv);

			if (widget % 3 == 1) {

				/* Increase button clicked */

				val = min(val + sdb->interval, (int32)sdb->max);

			} else {

				/* Decrease button clicked */

				val -= sdb->interval;

				val = max(val, sdb->min);

			}

			/* save value in temporary variable */

			WriteValue(GetVariableAddress(&this->opt_mod_temp, &sd->save), sd->save.conv, val);

		}

	}

	virtual void OnInvalidateData(int data = 0)

	{

		uint i;

		const SettingDesc *sd = GetSettingFromName("difficulty.max_no_competitors", &i);

		for (i = 0; i < GAME_DIFFICULTY_NUM; i++, sd++) {

			const SettingDescBase *sdb = &sd->desc;

			/* skip deprecated difficulty options */

			if (!SlIsObjectCurrentlyValid(sd->save.version_from, sd->save.version_to)) continue;

			int32 value = (int32)ReadValue(GetVariableAddress(&this->opt_mod_temp, &sd->save), sd->save.conv);

		}

	}

};

static NWidgetBase *MakeDifficultyOptionsWidgets(int *biggest_index)

{

	NWidgetVertical *vert_desc = new NWidgetVertical;

	int widnum = GDW_OPTIONS_START;

	uint i, j;

	const SettingDesc *sd = GetSettingFromName("difficulty.max_no_competitors", &i);

enum SettingGuiFlagLong {

	/* 1 byte allocated for a maximum of 8 flags

	 * Flags directing saving/loading of a variable */

	SGF_NONE = 0,

	SGF_0ISDISABLED  = 1 << 0, ///< a value of zero means the feature is disabled

	SGF_NOCOMMA      = 1 << 1, ///< number without any thousand seperators (no formatting)

	SGF_MULTISTRING  = 1 << 2, ///< the value represents a limited number of string-options (internally integer)

	SGF_NETWORK_ONLY = 1 << 3, ///< this setting only applies to network games

	SGF_CURRENCY     = 1 << 4, ///< the number represents money, so when reading value multiply by exchange rate

	SGF_NO_NETWORK   = 1 << 5, ///< this setting does not apply to network games; it may not be changed during the game

};

DECLARE_ENUM_AS_BIT_SET(SettingGuiFlagLong);

typedef bool OnChange(int32 var);           ///< callback prototype on data modification

typedef int32 OnConvert(const char *value); ///< callback prototype for convertion error

struct SettingDescBase {

	const char *name;       ///< name of the setting. Used in configuration file and for console

	const void *def;        ///< default value given when none is present

	SettingDescType cmd;    ///< various flags for the variable

	SettingGuiFlag flags;   ///< handles how a setting would show up in the GUI (text/currency, etc.)

	int32 min;              ///< minimum values

	uint32 max;             ///< maximum values

 * we also don't sync it in a network game */

#define S SLF_SAVE_NO | SLF_NETWORK_NO

#define C SLF_CONFIG_NO

#define N SLF_NETWORK_NO

#define D0 SGF_0ISDISABLED

#define NC SGF_NOCOMMA

#define MS SGF_MULTISTRING

#define NO SGF_NETWORK_ONLY

#define CR SGF_CURRENCY

#define NN SGF_NO_NETWORK

#define NG SGF_NEWGAME_ONLY

#define PC SGF_PER_COMPANY

static const SettingDesc _music_settings[] = {

	 SDT_VAR(MusicFileSettings, playlist,   SLE_UINT8, S, 0,   0, 0,   5, 1,  STR_NULL, NULL),

	 SDT_VAR(MusicFileSettings, music_vol,  SLE_UINT8, S, 0, 127, 0, 127, 1,  STR_NULL, NULL),

	 SDT_VAR(MusicFileSettings, effect_vol, SLE_UINT8, S, 0, 127, 0, 127, 1,  STR_NULL, NULL),

	SDT_LIST(MusicFileSettings, custom_1,   SLE_UINT8, S, 0, NULL,            STR_NULL, NULL),

	SDT_LIST(MusicFileSettings, custom_2,   SLE_UINT8, S, 0, NULL,            STR_NULL, NULL),

	SDT_BOOL(MusicFileSettings, playing,               S, 0, true,            STR_NULL, NULL),

	SDT_BOOL(MusicFileSettings, shuffle,               S, 0, false,           STR_NULL, NULL),

	 SDT_END()

};

 * service_interval value to the v->service_interval, meaning that every client

 * assigns his value. If the setting was company-based, that would mean that

 * vehicles could decide on different moments that they are heading back to a

 * service depot, causing desyncs on a massive scale. */

const SettingDesc _settings[] = {

	/***************************************************************************/

	/* Saved settings variables. */

	/* Do not ADD or REMOVE something in this "difficulty.XXX" table or before it. It breaks savegame compatability. */

	 SDT_CONDVAR(GameSettings, difficulty.max_no_competitors,        SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     2,0,MAX_COMPANIES-1,1,STR_NULL,                                  DifficultyChange),

	SDT_CONDNULL(                                                            1, 97, 109),

	 SDT_CONDVAR(GameSettings, difficulty.number_towns,              SLE_UINT8, 97, SL_MAX_VERSION, 0,NG,     2,     0,      4,  1, STR_NUM_VERY_LOW,                          DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.number_industries,         SLE_UINT8, 97, SL_MAX_VERSION, 0,NG,     4,     0,      4,  1, STR_NONE,                                  DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.vehicle_costs,             SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     0,     0,      2,  1, STR_SEA_LEVEL_LOW,                         DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.competitor_speed,          SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     2,     0,      4,  1, STR_AI_SPEED_VERY_SLOW,                    DifficultyChange),

	SDT_CONDNULL(                                                            1, 97, 109),

	 SDT_CONDVAR(GameSettings, difficulty.vehicle_breakdowns,        SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     1,     0,      2,  1, STR_DISASTER_NONE,                         DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.subsidy_multiplier,        SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     2,     0,      3,  1, STR_SUBSIDY_X1_5,                          DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.terrain_type,              SLE_UINT8, 97, SL_MAX_VERSION, 0,NG,     1,     0,      3,  1, STR_TERRAIN_TYPE_VERY_FLAT,                DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.quantity_sea_lakes,        SLE_UINT8, 97, SL_MAX_VERSION, 0,NG,     0,     0,      3,  1, STR_SEA_LEVEL_VERY_LOW,                    DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.economy,                   SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     0,     0,      1,  1, STR_ECONOMY_STEADY,                        DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.line_reverse_mode,         SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     0,     0,      1,  1, STR_REVERSE_AT_END_OF_LINE_AND_AT_STATIONS,DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.disasters,                 SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     0,     0,      1,  1, STR_DISASTERS_OFF,                         DifficultyChange),

	 SDT_CONDVAR(GameSettings, difficulty.town_council_tolerance,    SLE_UINT8, 97, SL_MAX_VERSION, 0, 0,     0,     0,      2,  1, STR_CITY_APPROVAL_PERMISSIVE,                            DifficultyNoiseChange),

	 SDT_CONDVAR(GameSettings, difficulty.diff_level,                SLE_UINT8, 97, SL_MAX_VERSION, 0,NG,     0,     0,      3,  0, STR_NULL,                                  DifficultyReset),

	/* There are only 21 predefined town_name values (0-20), but you can have more with newgrf action F so allow these bigger values (21-255). Invalid values will fallback to english on use and (undefined string) in GUI. */

 SDT_CONDOMANY(GameSettings, game_creation.town_name,              SLE_UINT8, 97, SL_MAX_VERSION, 0,NN, 0, 255, _town_names,      STR_NULL,                                  NULL, NULL),

 SDT_CONDOMANY(GameSettings, game_creation.landscape,              SLE_UINT8, 97, SL_MAX_VERSION, 0,NN, 0,   3, _climates,        STR_NULL,                                  NULL, ConvertLandscape),

	 SDT_CONDVAR(GameSettings, game_creation.snow_line,              SLE_UINT8, 97, SL_MAX_VERSION, 0,NN, 7 * TILE_HEIGHT, 2 * TILE_HEIGHT, 13 * TILE_HEIGHT, 0, STR_NULL,     NULL),