SCUMM/Technical Reference/Room resources

SCUMM V1

A room resource is located as the first chunk in a LFL File.

Header

The room resource starts with a 28 bytes header containing the following information:

Location	Format	Data
0x00	UInt16LE	Size of the room resource chunk
0x02	???	Unknown
0x04	UInt16LE	Room width in tiles (always 0x1C or 0x3C)
0x06	UInt16LE	Room height in tiles (always 0x10 on NES)
0x08	???	Unknown (Always 0 on NES)
0x0a	UInt16LE	Offset to 1 byte for the tileset index, followed by 16 bytes of palette data, and then the RLE encoded nametable data (NES)
0x0c	UInt16LE	Offset to the RLE encoded attribute table (NES)
0x0e	UInt16LE	Offset to the mask flag location. A value of 0x01 is followed by the RLE encoded mask data, otherwise 0x01.
0x10	???	Unknown (On NES both these values are equal)
0x12	???	Unknown
0x14	UInt8	Number of objects in room
0x15	UInt8	Offset to number of boxes location
0x16	UInt8	Number of sounds in room (Always 0 on NES)
0x17	UInt8	Number of scripts in room
0x18	UInt16LE	Offset to exit script location
0x1a	UInt16LE	Offset to entry script location

All offsets are relative to the start of the chunk.

Note: Because of the following constraints:

• Offset to box number location is stored as an UInt8, thus must be within the first 255 bytes of the chunk
• The header takes 28 bytes
• The combined size of object image and object code offsets is 4 bytes per object

The total number of objects per room must be less than 57:

(256 - 28) / 4 = 57

Content

Object image offsets

From byte 0x1c starts the offsets to object images, 2 bytes per object:

Location	Format	Data
0x1c	UInt16LE	Offset to object 1 image location
0x1e	UInt16LE	Offset to object 2 image location
...	UInt16LE	Repeated objNum times

On the NES this is RLE encoded nametable and attribute table data based on the height and width of the object. The nametable data is encoded per row. These graphical updates are triggered in SCUMM by setState08 and clearState08. Objects that have no state changes must still have an entry and can point arbitrarily.

Object code offsets

Next starts the list of offsets to each object's data:

Location	Format	Data
0x1c + objNum * 2	UInt16LE	Offset to object 1 content location
0x1c + objNum * 2	UInt16LE	Offset to object 2 content location
...	UInt16LE	Repeated objNum times

See table below for a description of the object data.

Unknown data

At this point there are 4 bytes of unknown data on the NES.

Number of boxes

The number of boxes (boxNum) in the room is located at the offset specified in the header.

Location	Format	Data
Offset to number of boxes	UInt8	Number of boxes in room

Note: Some LFL files have unknown data between the last object code offset and the boxes number offset location. For most files however, the data is contiguous.

Boxes

If the number of boxes is greater then 0 then 1 byte later starts the boxes payload. Each box has 8 bytes described as follows:

Relative location	Format	Data
0x00	UInt8	uy
0x01	UInt8	ly
0x02	UInt8	ulx
0x03	UInt8	urx
0x04	UInt8	llx
0x05	UInt8	lrx
0x06	UInt8	mask
0x07	UInt8	flags

The flags byte has various uses including:

Flag Value	Meaning
0x08	X flip
0x10	Y flip
0x20	Unused in V1
0x40	Locked
0x80	Invisible

Boxes matrix table

The box matrix payload starts with an offset table that points to the beginning of each box's data. It is boxNum wide.

Box matrix

Immediately following the last box's data is the box matrix which determines how the boxes are connected.

There are a minimum of boxNum * boxNum entries read as UInt8. Each entry consists of at least two pairs of three bytes which determine how the boxes connect. The table allows more values to be used in each entry if necessary. Example pseudo code:

boxMatrix = [
[1, 1, 1,  1, 1, 0],
[1, 2, 2,  2, 2, 1],
[1, 2, 3,  3, 3, 2],
[2, 2, 3,  4, 4, 3],
[3, 3, 3,  4, 5, 4],
[4, 4, 4,  4, 5, 5]
];

function nextBox (from, to)
{
  var box = boxMatrix[from];
  if (box[0] <= to && to <= box[1])
    return box[2];
  if (box[3] <= to && to <= box[4])
    return box[5];
  return -1;
}

Tileset index

The two bytes of room data at 0x0a point to the tileset index which is used to look up the tileset details in a separate table. The tileset table provides the bank and memory offset for the given tileset.

Palettes

One byte later starts the background palettes for a total of 16 bytes.

Nametable data

Next starts the RLE encoded nametable data (NES). The room height and width at bytes 0x06 and 0x04 of the room data are used to determine how much data is decoded.

Attribute table data

The two bytes at 0x0c of the room data point to the RLE encoded attribute table (NES). The amount of data is decoded according to the room height and width.

Mask Flag

Byte 0x0e of the room data points to this mask flag. It has a value of 0x00 or 0x01.

Mask data

If the mask flag is 0x01 then the RLE encoded mask data is next. This is bitmap data where each bit corresponds to a single tile, so a single byte covers a row of 8 tiles. A bit value of 1 = masked (background priority), and 0 = unmasked (sprite priority). The bits in each byte are reversed (or read right to left) before they are applied.

Object image data

Next starts the data that is pointed to by the object image offsets beginning at byte 0x1c in the room data. This is RLE encoded nametable and attribute table data for each object. The amount of data for each object is based on the height and width of the object. The data is RLE encoded per row. These graphical updates are triggered in SCUMM by setState08 and clearState08.

Object code

The object code section has the following structure starting at its corresponding object code offset:

Object code header

Relative location	Format	Data
0x00	UInt8	Size of the object code chunk
0x02	???	Unknown (Always 0 on NES)
0x03	???	Unknown (Always 0 on NES)
0x04	UInt16LE	The object number (used to reference object in scripts). Because of the way the data is stored in-game, the object number must be 255 (0xFF) or less in order to be picked up.
0x06	??	Unknown (Always 0 on NES)
0x07	UInt8	X position of object
0x08	UInt8	Object parent state + Y position of object (0xSSSYYYYY). Parent state is always 0x04 if present and is used in combination with the Object parent value at 0x0a to hide objects behind doors (e.g. items in the refrigerator).
0x09	UInt8	Object width in tiles
0x0a	UInt8	Object parent
0x0b	UInt8	Walk to X position
0x0c	UInt8	Preposition + Walk to Y position (0xPPPYYYYY). Possible preposition values are: 0x001 = in, 0x010 = with, and 0x011 = on.
0x0d	UInt8	Object height in tiles + Actor facing direction (0xHHHHHDDD). Possible facing values are: 0x100 = left, 0x101 = right, 0x110 = front (facing the player), and 0x111 = back (facing away from the player).
0x0e	UInt8	Offset to object name

Note: The object code data starts at byte 15. The verb-script pairs terminate with a null byte (0x00). This means that the object name offset value is always an even number, 16 or above.

Object code content

Object code content contains 3 optional sections, in this order:

• 0 or more pairs of verb id and script offsets
• The name of the object
• 0 or more object scripts consisting of SCUMM bytecode

Object script offsets

Starting at byte 15, two UInt8 values are read at a time.

The first value is a the verb ID and the second value is an offset to the beginning of the object script. Multiple verbs can have the same offset. The verb IDs are as follows:

Verb ID	Meaning
0x01	Open
0x02	Close
0x03	Give
0x04	Turn On
0x05	Turn Off
0x06	Fix (Unused)
0x07	New Kid (Unused)
0x08	Unlock
0x09	Push
0x0A	Pull
0x0B	Use
0x0C	Read
0x0D	Walk To
0x0E	Get
0x0F	What is (Unused)
0xFF	All

This part ends with 0x00.

Object name

The object name starts at the offset specified in byte 0x0e of the object data. Each character is read until a 0x00 value is found.

Object scripts

The object scripts are composed of SCUMM bytecode. Each object script ends with 0x00 (SCUMM opcode for stopObjectCode()).