Action2/Sprite Layout

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Action2 Sprite Layout

Feature Version
Houses Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5
Industry Tiles Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5
Objects Supported by OpenTTD 1.11.1 Supported by TTDPatch 2.6 (alpha r2023)2.6
Airport Tiles Supported by OpenTTD 1.11.1 Not supported by TTDPatch

This Action2 defines a spritelayout for a tile. There are three formats available:

  • Basic format for a single groundsprite and a single building sprite.
  • Extended format for combining multiple sprites.
  • Advanced format with register offsets

Basic format for tiles with a single building sprite

 <Sprite-number> * <Length> 02 07/09/0F/11 <set-id> 00 <groundsprite> <buildingsprite> <xoffset> <yoffset> <xextent> <yextent> <zextent>
Element Size Description
<Sprite-number> dec A sequential sprite number
<length> dec The total number of bytes used in this action
02 B Defines action 02
07/09/0F/11 B feature 7=town buildings, 9=industry tiles, 0F = objects, or 11 airport tiles
<set-id> B ID for this definition
00 B Literal 0 (to distinguish this definition from random/variational lists)
<groundsprite> D Ground sprite for the building (see format below)
<buildingsprite> D The sprite of the building (see format below), can be zero to indicate that no building sprite should be displayed (useful for early building stages)
<xofs> B x-offset from northern tile corner (as a signed byte)
<yofs> B y-offset from northern tile corner (as a signed byte)
<xextent> B size of sprite in x direction
<yextent> B size of sprite in y direction
<zextent> B size of sprite in z direction

In the above, xofs, yofs, xextent, yextent and zextent define the 3D bounding box of the building sprite not including the ground sprite. The z-offset is always zero for buildings (TTD doesn't support floating buildings). Please note that xofs/xextent and yofs/yextent pairs that place the bounding box off the tile are not recommended.

Extended format using multiple combined sprites

Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.5 (2.0.1 alpha 55 vcs 3)2.5 Since TTDPatch 2.0.1 alpha 55 vcs 3, houses, industry (and object) tiles support an extended syntax as well, which looks as follows:

<Sprite-number> * <Length> 02 07/09/0F/11 <set-id> <num-sprites> <groundsprite> [<buildingsprite> (<xoffset> <yoffset> <zoffset> <xextent> <yextent> <zextent>) | (<xpixeloffset> <ypixeloffset> 80)] ...
Element Size Description
<Sprite-number> dec A sequential sprite number
<length> dec The total number of bytes used in this action
02 B Defines action 02
07/09/0F/11 B feature 7=town buildings, 9=industry tiles, 0F = objects, or 11 = airport tiles
<set-id> B ID for this definition
<num-sprites> B Number of following building sprites (the groundsprite mustn't be counted). Allowed range: 1 to 63 (0x01 to 0x3F). Supported by OpenTTD 1.2 (r22518)1.2 Not supported by TTDPatch Adding 0x40 makes the layout an Advanced Spritelayout with register modifiers ( see below).
<groundsprite> D Ground sprite for the building (see format below)
<buildingsprite> D The sprite to be drawn. Unlike the basic format, zero isn't allowed here.
-- for sprites defining a new bounding box --
<xofs> B x-offset from northern tile corner (as a signed byte)
<yofs> B y-offset from northern tile corner (as a signed byte)
<zofs> B z-offset from the ground
<xextent> B size of sprite in x direction
<yextent> B size of sprite in y direction
<zextent> B size of sprite in z direction
-- for sprites sharing their bounding box with the previous sprite --
<xpixeloffset> B x offset from the top left corner of the previous sprite
<ypixeloffset> B y offset from the top left corner of the previous sprite
80 B a literal 80h byte to distinguish from new-bounding-box definitions

Note: restrictions for sprites sharing their bounding box are the same as explained for station tiles.

Supported by OpenTTD 0.7 (r18959)0.7 Since OpenTTD r18959 you can draw multiple ground sprites for a tile, which is useful if you want to use the usual grass/water/concrete groundtile, but still need to add features to it without using a new bounding box. To do so use the syntax of sprites sharing the previous bounding box, but use it before the first bounding box definition. xpixeloffset and ypixeloffset refer to the usual spot of groundtiles.

Supported by TTDPatch 2.6 (r2313)2.6 The same feature is also partially supported in TTDPatch since TTDPatch 2.6 r2313: TTDPatch ignores the xpixeloffset and ypixeloffset fields and always uses (0,0) for the offset. If you are developing a GRF that needs to be compatible with both OpenTTD and TTDPatch, you should always keep xpixeloffset and ypixeloffset zero to get the same effect in both games.

Advanced sprite layout using register offsets

<Sprite-number> * <Length> 02 07/09/0F/11 <set-id> <0x40 + num-sprites>
    <groundsprite> <flags> [<register/value>]...
    [ <buildingsprite> <flags>
        ( <xoffset> <yoffset> <zoffset> <xextent> <yextent> <zextent> 
        | <xpixeloffset> <ypixeloffset> 80)
      [<register/value>]...
    ]...

Supported by OpenTTD 1.2 (r22518)1.2 Not supported by TTDPatch The spritelayout defines fixed spritesets to use from the Action 1. The registers can be used to individually select sprites from the spritesets instead of always using the construction stage. The registers are evaluated and their values are saved when the Action 2 sprite layout is evaluated. Other callbacks called during drawing (like CB 1E) have no effect on the used values of the registers.

Element Size Description
<Sprite-number> dec A sequential sprite number
<length> dec The total number of bytes used in this action
02 B Defines action 02
04/07/09/0F/11 B feature 4=stations, 7=town buildings, 9=industry tiles, 0F = objects, or 11 = airport tiles
<set-id> B ID for this definition
40 + <num-sprites> B Number of following building sprites (the primary groundsprite mustn't be counted). Allowed range: 1 to 63 (0x01 to 0x3F).
<groundsprite> D Primary ground sprite for the building (see format below)
<flags> W Flags for the primary ground sprite (see format below)
<register/value> V Registers / values to be used. Depending on <flags> (see format below)
<buildingsprite> D The sprite to be drawn. Unlike the basic format, zero isn't allowed here.
<flags> W Flags for the building sprite (see format below)
-- for sprites defining a new bounding box --
<xofs> B x-offset from northern tile corner (as a signed byte)
<yofs> B y-offset from northern tile corner (as a signed byte)
<zofs> B z-offset from the ground
<xextent> B size of sprite in x direction
<yextent> B size of sprite in y direction
<zextent> B size of sprite in z direction
-- for sprites sharing their bounding box with the previous sprite --
<xpixeloffset> B x offset from the top left corner of the previous sprite
<ypixeloffset> B y offset from the top left corner of the previous sprite
80 B a literal 80h byte to distinguish from new-bounding-box definitions
 
<register/value> V Registers / values to be used. Depending on <flags> (see format below)

Descriptions of elements

Sprite-number

This is just the number you are at.

Length

Count the number of bytes in this action.

Set-id

The set-ID that you want to define for this set. You can choose any value between 00 and FF, and you can reuse them within a grf file at a later point (if being equal to an existing set ID, the existing one is overwritten and the new one is used).

Sprite definition for ground and building sprites

The ground and building sprite fields have the following format:

Bits Version Content
0-13 Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5 Sprite number, exact meaning specified by bit 31
14-15 Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5 0: draw sprite normally, 1: draw sprite in transparent mode, 2: recolor sprite
16-29 Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5 Color translation special sprite number, see below
30 Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.5 (alpha 57)2.5 If set, sprite is drawn normally even in transparent buildings mode (for building sprites only)
31 Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.52.5 Sprite type, see below

Supported by OpenTTD 0.60.6 Supported by TTDPatch 2.5 (alpha 57)2.5 Since TTDPatch 2.0.1 alpha 57, the groundsprite value can be zero if no ground sprite is needed (this is useful if you need to draw custom foundations, see example). Ground sprites are always drawn normally, so bit 30 is ignored for them. Bit 30 may get a different meaning for ground sprites in a later version of TTDPatch, so please leave it zero for now. This does not apply to additional groundsprites using the "<xpixeloffset> <ypixeloffset> 80"-syntax (see above); for these bit 30 has the same meaning as for building sprites.

Colour translation special sprite number

This is used only if bits 14 or 15 are nonzero. Bits 16-29 must be the number of a regular TTD sprite containing a colour translation table (see below for available translation tables). For transparent mode, a suitable translation table is needed, e.g. that of TTD´s sprite number 802 (s.b.). See RecolorSprites for more information on the usage of transparent and recolouring sprites.

For houses, if no recolour sprite is given but recolouring is turned on in bits 14-15, there are two possibilities:

  • If you have callback 1E enabled, it is called to determine the colour mapping.
  • If callback 1E is disabled or fails, one of the colours specified in property 17 will be chosen randomly.

See RecolorSprites for a list of available colour translations.

For industry tiles, if this field is zero, but recolouring is turned on in bits 14 or 15, the colour of the containing industry will automatically be applied.

The ground sprite should be exactly the same size and shape as TTD's flat tile. In general, it shouldn't contain anything that has a z-dimension because any non-ground sprite will cover it.

Useful values for ground sprites:

Sprite number (decimal) Contents
3924 bare land
3981 grass
4061 water
4550 snow or desert (depending on climate)
1420 concrete

Please note that all the ground sprite becomes visible in "transparent buildings" mode, so you should draw parts that seem to be hidden as well.

Sprite type

If bit 31 is clear, the bottom 14 bits contain a regular TTD sprite number.

If bit 31 is set, the bottom 14 bits contain a number of a sprite set in the most recent action 1, and the used sprite is decided according to the current construction state and the number of sprites in the set:

  • if there's only one sprite, it's used always
  • if there are two sprites, the first is used during construction (stages 0-2), and the second is used for the finished building (stage 3)
  • if there are three sprites, the first will be used in the beginning of the construction (stage 0), the second will be used during the rest of the construction (stages 1 and 2) and the third will be used for the complete building (stage 3)
  • if there are four or more sprites, the first four will be used for the four construction stages. Sprites after the first four are always ignored.


Flags in advanced sprite layouts

<flags> is a bitset of word size with these meanings:

Bit Hex Parentsprite Groundsprite/Childsprite
0 0001 Skip bounding box including child sprites Skip sprite
1 0002 Add offset to sprite, disable default usage of construction stage or railtype-offset
2 0004 Add offset to recoloursprite
3 0008 Recolour sprite is from Action 1 (will be affected by the same construction stage resp. railtype-offsets as sprites, unless bit 2 is set)
4 0010 Add offset for <xoffset> and <yoffset> Add offset for <xpixeloffset>
5 0020 Add offset for <zoffset> Add offset for <ypixeloffset>
6 0040 Resolve sprite with Variable 10 set to a specific value[1]
7 0080 Resolve recoloursprite with Variable 10 set to a specific value[1]
8..15 Reserved, should be zero. If the GRF sets unknown bits, it will be disabled.
  1. 1.0 1.1 Only valid for stations: The Action 1/2/3 chain is resolved multiple times, sprites can be part of different Action 1: The associated value in <register/value> is the raw value (not a register!) to put into Variable 10 while resolving the sprites.
    • only allowed values currently 0-7
    • the value '2' is used when resolving custom foundations, (so, do not conflict with that)
    • even if the sprite is not from an Action 1, the value still defines which Action2 chains defines the values for the referenced registers.
    • The register for "Add offset to recoloursprite" is defined by the Action 1/2/3 chain with Variable 10 as defined for the recolour sprite.
    • The other registers are defined by the Action 1/2/3 chain with Variable 10 as defined for the sprite.
    • If no variable 10 values are defined, then station property 13 bit 0 takes effect; i.e. variable 10 is set to 0 or 1 depending on the bit and whether the first groundsprite is resolved or a different sprite. This applies to both the groundsprite and the palette of the groundsprite.

Register or value in advanced sprite layouts

These are the temporary storage registers to add to the individual parts. The register values are considered signed. The order of the registers is the same as the bits in <flags>. If a bit is not set, then no registers appears for it. Most bits require one register.

  • <xoffset> and <yoffset> can only be enabled together, using two registers,
  • the "skip bounding box"-register uses value 1 to draw the sprite, and 0 to skip it,
  • the "recolorsprite from Action 1" uses no register at all,
  • the Variable 10 values are not set via a register, but via a byte-constant.