Macro

A macro is a form of compiled script used by the Doom 64 port. Similar to ACS in function, albeit significantly more limited, it provides the ability to execute groups of linedef specials. Virtually all specials in the Doom 64 engine can be executed from a macro, and there are numerous specials implemented in the game engine which are provided expressly for the purpose of setting variables or controlling the execution of macros, and therefore only work properly when used in that manner.

Language
The original language used to generate the lumps for Doom 64 is unfortunately unknown, but some of its qualities can be inferred from statements made by mappers Randy Estrella and Tim Heydelaar in public interviews. They stated that the language was somewhat similar to. As the original language is unknown, tools provided with the Doom64 EX source port provide an independent implementation for generating new macros which is purely conjectural.

Capabilities
In terms of capabilities, the scripting itself is not, as basic numeric and logical operations cannot be directly carried out. There is also no ability to jump or loop; all apparently looping macros are actually executing an unrolled set of instructions a preset number of times. Thus various traps such as darts shooting from walls can always be waited out and will eventually cease. An additional trigger must be provided in order to restart such a trap after it has finished.

Commands in each macro list the tag and special to execute, and are grouped into batches. Each batch of line actions occurs simultaneously, and the next batch will not execute until all actions in the current batch have finished. This is the only form of flow control implemented.

Use of certain tags on macro trigger lines will cause their macros to be executed at level start, much like ACS scripts.

Macros are also able to store and use a single global variable. There is a special (204) that allows to set it to an arbitrary value, and several specials that will refer to this value for their effects. Some of the specials using this value interpret it as a fixed point 16.16 value, in other word, 1.0 is expressed as 65536.

The game engine also has a fundamental and severe limitation: only one macro is allowed to execute at a time, globally. The game will queue the execution of any other macros if one is currently running, up to a currently unknown limit. As a result, this can allow speedrunners to abuse faster-than-intended movement to block execution of troublesome traps. It can also occasionally result in game-breaking glitches, as the layouts of levels can become non-negotiable if some macros fail to execute.

Format
The lump is an essential and required feature of the Doom 64 map format. It is a flat file of binary structures with the following layouts. All numeric fields are.

There is exactly one lump header, at offset zero in the lump:

For every macro enumerated in the first field of the lump header, the macro header structure occurs between lists of commands associated with that macro. The header for the next macro occurs after one plus the number of commands counted in this header, as there is always one "junk" command at the end of each macro which contains apparently uninitialized data and must be ignored by the reading application:

As mentioned above, each macro header is followed by a list of "number of commands" + 1 of the following structure. The final command not included in the macro header's count of commands is garbage data.

Macro specials
Line specials starting from 200 are meant to be used with macros.