The BEHAVIOR lump is part of the Hexen map format, and stores the bytecode of compiled ACS scripts, which are output created by the ACC compiler tool. Given the difference in records size between the Doom and Hexen format for THINGS and LINEDEFS lump, the presence or absence of a BEHAVIOR lump also serves to identify the format of the entire map in ports which support several different formats.
Lump structure[edit]
The BEHAVIOR lump contains compiled ACS scripts for the map. There exist three different formats for BEHAVIOR lumps, the original Hexen one is identified by a four-byte header of ACS\0 (0x41435300); ZDoom also uses two different "enhanced" formats identified by ACSE (0x41435345) and ACSe (0x41435365).
Behavior lumps are compiled with ACC. The version of ACC maintained by Marisa Heit (Randi) needs the -h command line parameter to produce ACS\0 bytecode, since many of the ACS functions it supports are only available in the ZDoom formats.
The Eternity Engine's ACS VM can now interpret all three bytecode formats.
ACS0 bytecode format[edit]
Lump header
| Offset |
Size |
C99 data type |
Field name |
Purpose
|
| 0 |
4 |
int32_t |
marker |
Must be 0x41435300 ("ACS\0")
|
| 4 |
4 |
int32_t |
infoOffset |
Offset to script directory from start of lump[notes 1]
|
Script directory
| Offset |
Size |
C99 data type |
Field name |
Purpose
|
| 0 |
4 |
int32_t |
ACScriptCount |
Number of scripts in directory; 0 if empty[notes 2]
|
| 4 |
12 * ACScriptCount |
|
info[] |
Array of script information structures
|
| 4 + 12 * ACScriptCount |
4 |
int32_t |
ACStringCount |
Number of strings in string table
|
| 8 + 12 * ACScriptCount |
4 * ACStringCount |
|
strings[] |
Array of string table entries
|
Script information structure
| Offset |
Size |
C99 data type |
Field name |
Purpose
|
| 0 |
4 |
int32_t |
number |
Script number
|
| 4 |
4 |
int32_t |
offset |
Offset to bytecode instruction stream from start of lump
|
| 8 |
4 |
int32_t |
argCount |
Number of arguments to script (only 0 to 3 are valid)[notes 3]
|
String table entry
| Offset |
Size |
C99 data type |
Field Name |
Purpose
|
| 0 |
4 |
int32_t |
offset |
Offset to null-terminated string data from start of lump
|
- ↑ Offset validation for all offset fields is minimal in the vanilla Hexen executable; invalid values may cause undefined behavior.
- ↑ Lump cannot be empty in vanilla Hexen; a map with no scripts must have a valid header containing 0 in this field instead. Program behavior is undefined otherwise.
- ↑ Negative values or values greater than 3 may cause undefined behavior in the vanilla Hexen executable.
Instructions[edit]
See also[edit]
External links[edit]
