SCUMM/Technical Reference/Script resources

SCUMM/Technical Reference → Script resources

Scripts control the internal logic of the games. They exist in different flavours:

global scripts
local scripts
room entry scripts
room exit scripts
object scripts

Starting with Scumm V5, the blockname contains 4 bytes and the block size is BE including the 8 bytes for the header. Older games just have a 2 bytes blockname and the block size is in LE without the 6 bytes for the header.

Global Scripts (SC or SCRP)

Global scripts are limited to 200 and stored in the LF or LFLF container. The id and the offset is stored in the directory of scripts in the game index file.

Block name         2 ("SC") or 4 ("SCRP") bytes
Block size         4 bytes 
Script code        variable

Local Scripts (LS or LSCR)

Local scripts are stored within a room. For games until version 6, the first byte after the blockname contains the id of the script. IDs for local scripts always start at 200.

Block name         2 ("LS") or 4 ("LSCR") bytes
Block size         4 bytes
ID                 1 byte
Script code        variable

For v7 and v8 games the script id is stored in 2 bytes and starts with 2000.

Block name         4 bytes ("LSCR")
Block size         4 bytes
ID                 2 bytes
Script code        variable

Room Entry Scripts (EN or ENCD)

This block contains special code when a room is entered.

Block name         2 ("EN") or 4 ("ENCD") bytes
Block size         4 bytes
Script code        variable

Room Exit Scripts (EX or EXCD)

This block contains special code when the player leaves a room

Block name         2 ("EX") or 4 ("EXCD") bytes
Block size         4 bytes
Script code        variable

Object Scripts V5+ (OBCD)

These are scripts that correspond to VERB actions. VERBs are predefined activities at the bottom of the screen, e.g. "Open", "Look", "Give" etc. For each named object in a room, the game designer could define responses to the players actions. A single VERB block contains the code for all possible player actions on the object. Starting with version 5, the whole code can be found in an Object Resource.

OBCD    
  Block name       4 bytes ("OBCD")
  Block size       4 bytes

   CDHD
     Block name    4 bytes ("CDHD")
     Block size    4 bytes (25)
     obj id        2 bytes
     ...           see Object Resource

   VERB
     Block name    4 bytes ("VERB")
     Block size    4 bytes
     offset table  variable {
      verb          1 byte (0xFF is default)
      offset        2 bytes
     }
     table end     1 byte (must be 0x00)
     object code   variable

   OBNA
     Block name    4 bytes ("OBNA")
     Block size    4 bytes
     object name   null-terminated string

Object Scripts in V3/4 (OC)

In Version 3 and 4 the code can be found in the OC block:

OC
  Block size        4 bytes (LE)
  Block name        2 bytes ("OC")
  Object ID         2 bytes (LE)
  unknown           1 byte
  x pos             1 byte
  y pos, par. state 1 byte
  image width / 8   1 byte
  parent            1 byte
  walk_x            2 bytes (LE)
  walk_y            2 bytes (LE)
  height, actor dir 1 byte
  name offset       1 byte
  offset table      variable {
   verb             1 byte (0xFF is default)
   offset           2 bytes
  }
  table end         1 byte (must be 0x00)
  object name       null-terminated string
  object code       variable

This block contains all object data except for the actual image bitmap. Compare this to V5+ objects, where metadata is split into seperate CDHD and OBNA blocks.

Image width is given in strips, which are 8 pixels wide. The high bit of y pos is used to store the parent's state (0 or 1). Both x pos and y pos will be multiplied by 8 by the interpreter. The lower three bits (mask 0x07) of height are used to store actor dir. Name offset is the absolute offset of object name (or, if you prefer, the position after table end).

The offset table is a variable block like that used in the VERB block in later games, which contains the verb identifier (1 byte) and the absolute offset (2 bytes). The table end is marked with 0x00. Next is the object's name, which is a standard null-terminated string. After this follows the actual object code. Note that unlike other script types, because there are multiple entry points (one for each supported verb), there are also multiple exit points (or "stopObjectCode" instructions).