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Linedef

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Linedefs are what make up the 'shape' (for lack of a better word) of a map. Every linedef is between two vertices and contains one or two sidedefs (which contain wall texture data). There are two major purposes of linedefs. The first is to divide the map into sectors, and the second is to trigger action specials.

Any area of a map directly behind a one-sided linedef is void space (which cannot be occupied except by using the idclip cheat code). A two-sided linedef is needed (to separate the two sectors) any time there is a change in (1) the height or texture of the floor or ceiling, (2) the light level, or (3) the sector tag or type.

There are three ways to trigger an action:

  1. walkover
  2. "use" (or "push") (with the space bar, by default)
  3. shoot (with an impact weapon)

Which of these applies depends on the linedef type number, which also specifies what particular action will occur.

The specified action usually will take place in the sector or sectors that have the same tag number as the linedef. Exceptions to this include local doors (which act on the sector on the other side of the line), special effects that apply to the linedef itself, and the exit-level actions.

Most actions can be specified as either once-only or repeating (by using different linedef types).

Linedef structureEdit

Doom level format

Extensions:

Each linedef is 14 bytes long.

Doom
Offset Size (bytes) Description
0 2 Start Vertex
2 2 End Vertex
4 2 Flags
6 2 Special Type
8 2 Sector Tag
10 2 Right Sidedef 1
12 2 Left Sidedef 1

1. ^  The special value '-1' is used to indicate no sidedef, in one-sided lines.

Hexen / ZDoom
Offset Size (bytes) Description
0 2 Start Vertex
2 2 End Vertex
4 2 Flags
6 1 Special Type
7 1 Argument 1
8 1 Argument 2
9 1 Argument 3
10 1 Argument 4
11 1 Argument 5
12 2 Right Sidedef
14 2 Left Sidedef


Linedef flagsEdit

Linedefs contain a two-byte (16 bit) field reserved for various flags. Flags are as follows:

Bit
Hex
Description
ZDoom/Hexen ONLY
0
0x0001
blocks players and monsters

1
0x0002
blocks monsters

2
0x0004
two sided

3
0x0008
upper texture is unpegged

4
0x0010
lower texture is unpegged

5
0x0020
secret (shows as one-sided on

automap), and monsters cannot open if it is a door (type 1)


6
0x0040
blocks sound

7
0x0080
never shows on automap

8
0x0100
always shows on automap

9
0x0200
can be activated more than once
X
10-12
0x0400
activated when used by player
X
10-12
0x0800
activated when crossed by monster
X
10-12
0x0C00
activated when hit by projectile
X
10-12
0x1000
activated when bumped player
X
10-12
0x1400
activated when crossed by projectile
X
10-12
0x1800
activated when used by player (with

pass through)

X
13
0x2000
line can be activated by players and

monsters

X
14
0x4000

X
15
0x8000
blocks everything (includes

gunshots & missiles)

X

See also Edit

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