Inside Mac Games Volume 4 #1 & #2/IMG 34 JanFeb 1996.iso/More Goodies/Cheaters, Editors, et al./WolfEdit 1.1B ƒ/Level Format

Text File | 1995-09-16 | 12KB | 365 lines

        Wolfenstein 3D First Encounter Level Format
        ===========================================

                        Greg Ewing
                [e-mail]

Here is a summary of what I have learned about the format of the level
resources used by Wolfenstein 3D First Encounter.

1. Map List resource
--------------------

The Map List is in BRGR resource 146.  It begins with a 2-word header:

Offset    Size    Description
    0    word    Number of levels
    2    word    Resource ID of the first level

Following this is a 5-word entry for each level:

    0    word    Next level (offset from first level ID)
    2    word    Alternate next level
    4    word    Par time (seconds)
    6    word    Major floor number
    8    word    Minor floor number

2. Level resource
-----------------

The levels themselves are also kept in BRGR resources.  The ID of the first
level resource is determined by the map list as described above.  The
original levels use IDs 200 and upwards.

The level resource consists of a fixed-length part followed by a
variable-length part.  The fixed-length part can be further subdivided into
a map and a sound area table, and the variable-length part into a header,
an object table and a BSP tree.

2.1 Map
-------

The map section is 4096 bytes long, organised as a 64 by 64 grid.  Each
byte in the map represents either a solid block, a door or an empty space.
If bit 7 of the byte is 1, then it represents a solid block or door, and
the rest of the bits determine what kind of wall or door it is.

If bit 7 is 0, the byte contains a room number.  A room is a contiguous
space which is completely divided off from other rooms by walls or doors.
There may be up to 64 rooms, numbered 0 to 63.  Each byte in the map
representing an empty space contains the room number to which the space
belongs.

2.2 Sound Area table
--------------------

This is a 64-byte table containing a sound area number for each room.  When
you fire your gun, guards in rooms belonging to the same sound area can
hear you.  If they're not "shoot only on sight" guards, they will seek you
out.

WolfEdit 1.1 does not provide any way of setting sound areas; each room is
placed in a separate sound area.  (Note, however, that an area separated
from a room by a secret door is considered part of the same room.)

2.3 Header of variable-length part
----------------------------------

The variable-length part begins with a 4-word header.  Entries marked with
* are stored in little-endian byte order (least significant byte first).

    0    word    Number of objects
    2    word    Offset from start of resource to object table
    4    word    Number of entries in BSP tree
    6    word    Offset from start of resource to BSP tree

2.4 Object table
----------------

The object table contains an entry for each object appearing on the level.
Each entry is either 3 or 4 bytes long, depending on the object type.

    0    byte    x-coordinate of map cell (0 to 63)
    1    byte    y-coordinate of map cell (0 to 63)
    2    byte    Object type

If the object type is $62, then the object is a secret door.  In the map, a
secret door appears as an empty space, and there is an extra byte in the
object table entry containing the wall type:

    3    byte    Wall type of secret door (object type $62 only)

2.5 BSP tree
------------

2.5.1 About the BSP tree

A Binary Space Partitioning or BSP tree is used to divide the map space up
into portions in such a way that the rendering engine can efficiently
determine which parts are visible.

The BSP tree consists of two types of nodes, terminal and non-terminal.
Each node corresponds to some rectangular portion of the map.  A
non-terminal node is further subdivided into two child nodes.  A terminal
node is not subdivided any further and has no children; it is a "leaf" of
the tree.

A terminal node consists of a collection of segments.  A segment represents
part of a wall - a boundary between an empty and a filled-in region of the
map.

The coordinate system used to describe segments has twice the resolution of
the map cell coordinate system used in the object table.  Furthermore,
instead of referring to cells, segment coordinates refer to the dividing
lines between cells.  So, whereas cell coordinates range from 0 to 63,
segment coordinates range from 0 to 128.  Even segment coordinates
correspond to the lines running between map cells; odd segment coordinates
refer to lines which pass through the middle of map cells.  (The reason for
this will become clear later.)

Each segment is described by three coordinates.  For segments running
east-west these are its position in the y direction and the x-coordinates
of its two endpoints.  For segments running north-south, the roles of x and
y are reversed.

Each segment also faces in a particular direction.  An east-west segment
can face either north or south, and a north-south segment can face either
east or west.  The direction a segment faces determines from which side it
will be visible; the rendering engine doesn't bother drawing segments which
are facing away from you.

A terminal node of the tree contains a collection of segments such that no
segment can obscure part of any other segment from any viewing position.

2.5.2 Format of the BSP tree

The BSP tree consists of a sequence of 6-byte entries, numbered from 0.
The root node of the tree begins at entry 0.

Each non-terminal node takes up one entry structured as follows:

    0    byte    Split coordinate

                        For an east-west split, this is the y-coordinate
                        of the splitting line; for north-south, the
                        x-coordinate.

    1    byte    Flags    Bit 7 of this byte is 0, indicating a non-terminal
                        node. Bit 0 indicates the direction along which
                        the space covered by this node is split to create
                        the subspaces of its child nodes. 0 means the
                        splitting line runs east-west, 1 north-south.

    2    word*    First child

                        Entry number of the first child node. The subspace
                        covered by this child is the one with coordinates
                        *greater* than that of the splitting line.

    4    word*    Second child

                        Entry number of the other child node.

The coordinates of the region covered by each node are not explicitly
stored in the node; rather, they are implicit in the coordinates of the
splitting lines at each step, and the fact that the root node covers the
whole of the map.

Each terminal node takes up one entry for each segment as follows:

    0    byte    Segment position

                        For an east-west (or north-south) segment, this is
                        the positition of the segment in the y (or x)
                        direction.

    1    byte    Flags    Bit 7 of this byte is 1, indicating a terminal
                        node. Bit 6 is set to 1 if this is the last segment
                        belonging to this node; 0 if more are to follow.
                        Bits 1 and 0 indicate the orientation of the
                        segment:

                            00    North-south, facing east
                            01    East-west, facing south
                            10    North-south, facing west
                            11    East-west, facing north

    2    byte    Start coordinate
    3    byte    End coordinate

                        For east-west (or north-south) segments, these
                        are the x (or y) coordinates of the segment's
                        endpoints.

    4    byte    Map row/column

                        For east-west segments, this is the map cell
                        coordinate (0 to 63) of the map row containing
                        the wall block immediately behind the segment.
                        For north-south segments, it is the column
                        number plus 64.
                        (For segments associated with doors, this byte
                        has a different interpretation - see below.)

    5    byte    Room number

                        This is the room number of the room into which
                        the segment faces.

2.6 Doors
---------

A door is represented by an entry in both the map and the object table, the
object having the same code as the map entry with bit 7 set to 0.  Bit 0 of
the door code indicates the direction of the door: 0 for a doorway leading
east-west, 1 for north-south.

Associated with a door are four special segments, one each side of the door
facing inwards, and one along each face of the door itself (the sliding
part).  The latter two are positioned in the middle of the map cell
containing the door.

The side segments have byte 4 of the segment entry set to $80.  The sliding
segments have this byte set to $80 plus the door number: each door on a
level has a unique number from 1 upwards.

2.7 Lifts
---------

The lift control panel and the side panels with hand railings are
represented in the map by the same code ($8F).  If you are looking at the
east or west face of the block, it appears as a lift control panel; if you
are looking at the north or south face, it appears as a hand railing.

However, the lift control panel also has an object with a code of $64 at
the same location.  It is the presence of this object which causes the
block to behave like a lift when you operate it.  If this object is not
present, the control panel is just another piece of wall.  Conversely,
placing a $64 object on top of some other type of wall will make it behave
like a lift.  This could allow for some very unfair levels...

2.8 Hidden passages
-------------------

The secret blocks which move back when you push on them involve special
arrangements in the map, object table and BSP tree.  In the map, the
location of the secret block is an empty space, and the area to which it
leads is part of the same room as the area it leads from.

An object with code $62 is placed at this location: this is the object you
operate when you push on the block.  The object table entry for this object
has an extra byte appended, containing the wall code which would otherwise
have been placed in the map at that location.

The secret block has two segments associated with it.  One of them is
positioned on the outside of the block in its initial position, facing
towards the player as he stands in front of the block ready to push it.
The other segment is positioned on the other side of the block, but facing
in the same direction - in other words, it is in the place the first
segment would end up after the block had been pushed one map cell.  Byte 4
of both these segments refer to the block's initial location.

It is also necessary to place an ordinary block of the same type two cells
away in the direction of motion, i.e.  in the place where the secret block
will end up after it has been pushed.  If this is not done, not only will
the block vanish after opening, but for some strange reason it may not
display properly in its initial position.

2.9 Map codes
-------------

Here is a list of the codes which may be placed in the map for various
types of walls and doors.

2.9.1 Wall codes

$81    Grey stone
$82    Grey stone with archway and eagle emblem
$83    Grey stone with swastika wall hanging
$84    Grey stone with Hitler portrait
$85    Wood panelling
$86    Wood panelling with eagle emblem
$87    Wood panelling with Hitler portrait
$88    Wood panelling with purple cross
$89    Blue stone
$8A    Blue stone with cell door
$8B    Red brick
$8C    Red brick with eagle emblem
$8F    Lift side wall or control panel
$91    Metal plate
$9A    Yellow stone with blood stain
$9B    Yellow stone blocks
$9D Concrete(?) blocks

2.9.2 Door codes

$DA    Plain east-west
$DB    Plain north-south
$DD    Gold key north-south    (Note: there is no gold key east-west door!)
$DE    Silver key east-west
$DF    Silver key north-south
$E0    Lift door east-west
$E1    Lift door north-south

2.10 Object codes
-----------------

Here is a list of codes which may be placed in the object table.

2.10.1 Player starting positions

$13    Facing north
$14    Facing east
$15    Facing south
$16    Facing west

2.10.2 Ornaments

$17    Puddle
$18    Oil drum
$19    Table
$1A    Standard lamp
$1B    Chandelier
$1E    Tree
$1F Flag pole
$20    Pot plant
$21    Urn
$22    Bones
$23    Ceiling light
$24    Bowl
$25    Suit of armour
$26    Hanging cage
$36    Water tub
$37  Dog crap

2.10.3 Useful items

$1C    Dog food
$27    Gold key
$28    Silver key
$29 Backpack
$2A    Ammunition box
$2B    Food
$2C First aid kit
$2D    Ammunition clip
$2E    Machine gun
$2F    Gatling gun
$34    Extra life
$35  BigDickey

2.10.4 Treasures

$30    Jewelled cross
$31    Goblet
$32    Treasure chest
$33    Crown
$34  Crap

2.10.5 Enemies

$6C    Brown uniform
$6E    Blue uniform
$6F    Dog
$71    Boss
$7E    Brown uniform, waiting to ambush