ActionD

Introduction

Assign parameters and calculate results.

Action D allows you to set the value of grf parameter (i.e. those usually set as options in the newgrf(w).cfg file), as well as do math on them.

Syntax

The data looks as follows:

<Sprite-number> * <Length> 0D <target> <operation> <source1> <source2> []

Element	Size	Description
<Sprite-number>	dec	A sequential sprite number
<length>	dec	The total number of bytes used in this action
0D	B	Defines action 0D
<target>	B	Target parameter
<operation>	B	Calculation to carry out
<source1>	B	First argument
<source2>	B	Second argument
	D	Value to use as source if not parameter

Description

target, source1, source2

These bytes specify the target parameter and source parameters. They can either be simply the numbers of grf parameters, or they can be the special variables from action 7, see the description of param-num there.

Note that the only special variables which may be given as target are listed below, all others should be considered read-only.

If either source1 or source2 is FF, the value from is used instead of a parameter value.

If <source2> is FE, then this action D will perform one of the following special variable accesses. In this case, <operation> must be assignment and is an argument to the data access, not a source value.

• Read parameters of another GRF
• Read game configuration settings
• Reserve GRF resources to prevent conflicts with other GRFs

operation

The operation to carry out on the source arguments. This byte has an escape sequence for each of its possible values, as listed below. See the discussion of escape sequences for further information on escape sequences in general. The result of this calculation will be stored in the target parameter.

Operation	Escape	Version	Name	Result
00	\D=		Equal	target = source1
01	\D+		Addition	target = source1 + source2
02	\D-		Subtraction	target = source1 - source2
03	\Du*		Unsigned multiplication	target = source1 * source2, with both sources being considered to be unsigned
04	\D*		Signed multiplication	target = source1 * source2, with both sources considered signed
05	\Du<<		Unsigned bit shift	target = source1 << source2 if source2>0, or target = source1 >> abs(source2) if source2 < 0. source1 is considered to be unsigned
06	\D<<		Signed bit shift	same as 05, but source1 is considered signed)
07	\D&	2.5	Bitwise AND	target = source1 AND source2
08	\D	2.5	Bitwise OR	target = source1 OR source2
09	\Du/	2.5	Unsigned division	target = source1 / source2
0A	\D/	2.5	Signed division	target = source1 / source2
0B	\Du%	2.5	Unsigned modulo	target = source1 % source2
0C	\D%	2.5	Signed modulo	target = source1 % source2

You can add 80 to the operation number to make it apply only if the target is not defined yet. In this respect, a parameter is taken to be defined if any of the following applies:

• it has been set to any value in the newgrf(w).cfg parameter list
• it or a parameter with higher number has been set to any value by an earlier action D

If, for example, parameters 0 and 1 are set in the newgrf(w).cfg file, and action D sets parameter 4, then parameters 2 and 3 automatically become defined and get a value of zero.

Notes

You can do a bitwise NOT of <param> by calculating "-1 - <param>", i.e. operation=02, source1=FF, source2=param, data=FF FF FF FF.

The target operand can also refer to the special variables from action 7, see below for the list of variables that it is valid to write to.

Because the patch has to reallocate memory for the whole parameter list whenever a new parameter is added, you should set the parameter with the highest number first (whenever possible, at least) so that all memory can be allocated right away.

Note that parameters are never reset after the game has started, therefore you must not modify newgrf(w).cfg parameters with any kind of irreversible operation. It is valid to, for example, add a value to a parameter only if the same value is later subtracted, to keep the parameter the same across loading or starting several games.

Those global variables which can be written to are indicated in a separate column in the global variable list. Note that Action D only supports writing dword values. The size given there is merely used to convey how much of that dword value will be used by the game, i.e. what the maximum value is.

Example

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