Action2/Advanced Sprite Layout

Advanced sprite layout using register offsets

1.2  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 groundsprite mustn't be counted). Allowed range: 1 to 63 (0x01 to 0x3F).
<groundsprite>	D	Ground sprite for the building (see format below)
<flags>	W	Flags for the 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
<register/value>	V	Registers / values to be used. Depending on <flags> (see format below)
80	B	a literal 80h byte to distinguish from new-bounding-box definitions

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	0.6 2.5	Sprite number, exact meaning specified by bit 31
14-15	0.6 2.5	0: draw sprite normally, 1: draw sprite in transparent mode, 2: recolor sprite
16-29	0.6 2.5	Color translation special sprite number, see below
30	0.6 2.5	If set, sprite is drawn normally even in transparent buildings mode (for building sprites only)
31	0.6 2.5	Sprite type, see below

0.6 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
7	0080	Resolve recoloursprite with Variable 10 set to a specific value
8..15		Reserved, should be zero. If the GRF sets unknown bits, it will be disabled.

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.