GlobalVariables

Overview

Variable			Size	Description
VA2	A6/7/9	ActD
00	80		W	0.6 ?? current date (counted as days from 1920)
01	81		B	0.6 ?? Current year (count from 1920, max. 2175 even with eternalgame)
02	82		B/D	0.6 ?? current month (0-11) in bits 0-7; the higher bytes contain unusable junk. 0.7  Since OpenTTD r13594 'day of month' (0-30) is stored in bits 8-12, bit 15 is set in leapyears and 'day of year'(0-364 resp. 365) is stored in bits 16-24. All other bits are reserved and should be masked.
03	83		B	0.6 ?? Current climate: 00 = temp, 01 = arctic, 02 = trop, 03 = toyland
	84		D	0.6 ?? GRF loading stage, see below
	85		B	0.6 ?? TTDPatch flags: only for bit tests
06	86		B	0.6 ?? Road traffic side: bit 4 clear=left, set=right
	88		4*B	0.6 ?? Checks specified GRFID (see condition-types below)
09	89		W	0.6 ?? date fraction, incremented by 0x375 every engine tick
0A	8A		W	0.6 ?? animation counter, incremented every tick
0B	8B		D	0.6 ?? TTDPatch version, see below
0C			W	0.6 ?? current callback ID (feature-specific), set to 00 when not in a callback
0D	8D		B	0.6 ?? TTD version, 0=DOS, 1=Windows
0E	8E	8E	B	0.6 ?? Y-Offset for train sprites
0F	8F	8F	3*B	0.6 ?? Rail track type cost factors
10			D	0.6 ?? extra callback info 1, as described in the callback specs
11			B	?? current rail tool type (for station callbacks)
12	92		B	0.6 ?? Game mode, 0 in title screen, 1 in game and 2 in editor
13	93	93	W	2.5 Tile refresh offset to left
14	94	94	W	2.5 Tile refresh offset to right
15	95	95	W	2.5 Tile refresh offset upwards
16	96	96	W	2.5 Tile refresh offset downwards
17	97	97	B	?? Snow line height
18			D	0.6 ?? extra callback info 2, as described in the callback specs
	99	99	D	?? Global ID offset
1A	9A		D	0.6 ?? Has always all bits set; you can use this to make unconditional jumps
1B			B	?? display options; bit 0=town names, 1=station names, 2=signs, 3=animation, 4=transparency, 5=full detail
1C			D	0.6 ?? result from most recent VarAction2
1D	9D		D	0.6 ?? TTD Platform, 0=TTDPatch, 1=OpenTTD
1E	9E	9E	D	0.6 ?? Misc. GRF Features
		9F	D	?? writable only: Locale-dependent settings
20			B	0.6 ?? snow line height, FFh if snow isn't present at all
21	A1		D	?? OpenTTD version, see below.
22	A2		D	0.7 ?? Difficulty level: 00= easy, 01=medium, 02=hard, 03=custom
23	A3		D	0.7 2.6 Current date long format
24	A4		D	0.7 2.6 Current year zero based
25			D	0.7  GRFID of the grf that contains the corresponding Action3. Useful when accessing the "related" object. Currently only supported for vehicles.

All other variable numbers are reserved and must not be used.

Special variables

GRF Loading stage (84)

Variable 84 is a BYTE variable up to TTDPatch 2.5r1220. Its lower byte (bits 0..7) are 0 for the post-load and GRF initialization stages and 01 for all other stages. The remaining bits are a bitmask, and including the lower byte have the following meaning:

Bit	Meaning
0	Set after the "Initialization" stage completes
1..7	Always clear
8	Set during the "Reserve" stage only
9	Set during the "Activate" stage only
10	Set during the "Test" stage only

TTDPatch Version (8B)

Variable 8B has the following format: MMmrbbbb (though encoded in little endian as bb bb mr MM)

Element	Meaning	Value
MM	major	First number of the TTDPatch version
m	minor	Second number of the TTDPatch version
r	revision	Third number of the TTDPatch version*
bbbb	build	Alpha/beta version number times ten (up to an including TTDPatch 2.5 beta 5), SVN revision (from TTDPatch 2.5 beta 5 r418 on)

Examples

Version	Variable 8B	Elements
1.9.1 alpha 50	019101F4	MM=01, m=9, r=1, bbbb=50*10=01F4
2.0 beta 4	02040028	MM=02, m=0, r=4*, bbbb=4*10=0028
2.0 final	02070046	MM=02, m=0, r=7*, bbbb=70=0046
2.0 rev 1	02070050	MM=02, m=0, r=7*, bbbb=80=0050
2.0.1 alpha 3	020A001E	MM=02, m=0, r=10*, bbbb=3*10=001E
2.5 beta 2	02500014	MM=02, m=5, r=0, bbbb=2*10=0014
2.5 rev631	02500631	MM=02, m=5, r=0, bbbb=631=0631

(*) For TTDPatch 2.0, r=7 and for TTDPatch 2.0.1 series, r=10 due to an oversight which used r=1..4 for TTDPatch 2.0 beta 1..4.

To detect versions from TTDPatch 2.5 rev419 and up correctly, check that var. 8B is 02500419 or higher, or replace 0419 with the actual required revision (using the revision number as hex digits). Because SVN revisions are shared with other patch branches, it is important to check the actual patch version as well as the SVN revision.

Y-Offset for train sprites (8E)

Since train sprites must normally have the same offsets on the map and in the depot view, they will appear either too low on the map or too high in the depot view. This variable moves all vehicles in the depot view down by this many pixels.

Since OpenTTD r16867 this variable works per grf file, that is: It only affects trains defined in the same grf.

Rail track type cost factors (8F)

This variable is a collection of three bytes that are used as multipliers for track costs when the "trackcostdiff" switch is on. The value of 08 is the baseline value that is used by standard TTD.

The defaults are the following:

Values	Track types	Electrified railways setting
08, 10, 18	Regular, Monorail, Maglev	off
08, 0D, 10	Regular, Electric, Monorail/Maglev	on

Tile refresh offsets (93, 94, 95, 96)

These four offsets define the size and position of the rectangle refreshed when TTD decides to refresh a tile. The basis of the calculations is the pixel coordinate of the north corner of the tile.

After calculating it, TTD subtracts offset_left from it to get the x coordinate of the left edge, adds offset_right to get the x coordinate of the right edge, subtracts offset_up to get the y coordinate of the top edge and adds offset_down to get the y coordinate of the bottom edge. This results in refreshing (offset_left+offset_right)*(offset_up+offset_down) pixels. The default values of these variables are 31, 36, 122 and 32, respectively.

Reading these values is not too useful, but you can modify them using action D as well, so your sprites that would exceed the original limits can still be redrawn and animated properly. Please note that TTD uses these values for every tile, so specifying too high values may slow the game down. Please also note that these variables are specified as dwords for technical reasons, but only the bottom word will be used.

Since these values are global to the entire game, you shouldn't just overwrite them with an action D. Instead, you should first check if they're big enough for you by using action 7, and skip your action D if they are. This way, the variables will be set to the maximal value needed, not just the value needed for the last grf in the list.

Snow line height (97)

This is only active if the tempsnowline switch is on. It defaults to FF (no snow) and 38 in the temperate and arctic climates, respectively. It must be set to a multiple of 8, which is one level of height difference.

Global ID offset (99)

Setting this variable will add the given value to all the relevant IDs in subsequent action 0, action 3 (except livery overrides), action 4 (except generic texts) and action A entries. This is a more convenient way of applying the result of a GRF resource request. Setting this variable applies only to the current .grf file only.

In detail, it affects the following elements:

Action	Element modified
0	<Id> (i.e., not property numbers)
3	<Ids...> (i.e., not cargo types or cargo IDs, also not for livery overrides)
4	<Offset> (not for generic texts, though)
A	<First-sprite>

Misc. GRF Features (9E)

This variable is a global bit mask of various patch features a grf file can enable. Please only set the bits using operation 08 (bitwise OR), or, if absolutely necessary, remove certain bits with operation 07 (bitwise AND). This ensures that you don't mess up the settings of other grf files.

Bit	Value	Feature	Min. version
0	1	Allow trees and fields in the desert
1	2	Show pavement and lights in desert towns
2	4	Fields have a height, using a 3D bounding box
3	8	Display train vehicles with full width of 32 pixels in depot window (instead of 29 pixels)	(a)
4	10	Enable ambient sound effect callback 144	TTDPatch 2.6 r821
5	20	Enable catenaries over the third track type (only with electrifiedrailway on)	TTDPatch 2.6 r826, TTDPatch 2.5 r1439 (beta 10)
31	80000000	Only to be set by ttdpbase(w).grf for identification

(a) Since OpenTTD r16867 this flag works per grf file, that is: It only affects trains defined in the same GRF.

Example code for setting bit 3:

  24 * 9     0D 9E 08 9E FF 08 00 00 00

(Here, the first 08 indicates the bitwise OR operation, and 08 00 00 00 is the value to OR var.9E with.)

Locale-dependent settings (9F)

This variable is a doubleword in the format rrccmmll, where the meaning of the bytes is:

Byte	Meaning
rr	Reserved for future use, just put zero here for now
cc	Default currency to be used when the game is first started. It can be larger than 5 to select one of the currencies added via morecurrencies. If this value is larger than 5 while morecurrencies is disabled, US dollars will be used instead.
mm	Default measurement system to be used when the game is first started. 00h means the imperial system (miles), 01h means the metric system (kilometers), other values are forbidden.
ll	Language ID. By setting this byte, you can override the default language ID and allow other GRFs to supply correctly localized texts. (The other GRF can check for this value in action 4s)

Reading this variable isn't reliable, so you must only write to it. Please also note that the cc and mm parts are considered only while loading the title screen for the first time, changing them later is ignored.

NOTE: This variable is reset after the initialization stage. Only changes during the activation stage are considered. This way, GRFs disabled in newgrf.cfg won't change the language and/or default settings. If you want to modify the cc or mm part, make sure the corresponding action D isn't skipped by an earlier action 7 or 9. In particular, if your GRF isn't available for the tropic climate, make sure you set variable 9F before the climate check, since the default title screen is tropic, and your climate check will fail on it.

OpenTTD Version (A1)

Variable A1 has the following format: Mmrbbbbb (though encoded in little endian as bb bb rb Mm). This variable has only a usefull meaning when variable 9D is 1 (OpenTTD). This variable can be used since OpenTTD r11330.

Element	Meaning	Value
M	major	First number of the OpenTTD version
m	minor	Second number of the OpenTTD version
r	revision	Third number of the OpenTTD version
bbbbb	build	Subversion revision of a build leading towards a release. When a final release is done 80000h is set.

The presence of 80000h (bit 19 set) means that a release always has a higher version number than any builds leading to that release.