Linedef
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:
- walkover
- "use" (or "push") (with the space bar, by default)
- 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).
Contents
Linedef structure
Doom level format |
---|
Extensions: |
Each linedef is 14 bytes long.
Doom level format
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 Template:Ref |
12 | 2 | Left Sidedef Template:Ref |
Template:Note The special value '-1' is used to indicate no sidedef, in one-sided lines.
Hexen level format
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 flags
Linedefs contain a two-byte (16 bit) field reserved for various flags. Flags are as follows:
Doom level format
Bit | Hex | Description |
---|---|---|
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 |
Boom level format
Boom added one flag to Doom's linedef flags:
Bit | Hex | Description |
---|---|---|
9 | 0x0200 | The "use" action can activate other linedefs in the back (in Doom the "use" action only activates the closest linedef in the line of sight). Usually called "PassThru". |
Hexen level format
All Doom flags and also the following:
Bit | Hex | Description |
---|---|---|
9 | 0x0200 | can be activated more than once |
10-12 | 0x0400 | activated when used by player |
10-12 | 0x0800 | activated when crossed by monster |
10-12 | 0x0C00 | activated when hit by projectile |
10-12 | 0x1000 | activated when player bumps into it |
10-12 | 0x1400 | activated when crossed by projectile |
10-12 | 0x1800 | activated when used by player (with
pass through) |
13 | 0x2000 | line can be activated by players and
monsters |
14 | 0x4000 | |
15 | 0x8000 | blocks everything (includes
gunshots & missiles) |