Linedef
From DoomWiki.org
Doom level format |
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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:
- 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).
Which side is the front or back of a linedef is determined by which vertex is the first vertex. For example, if you were to draw many linedefs with different second vertexes, but the same first vertex, those linedefs would face "clockwise". The front is always 90 degrees to the right / clockwise from the ray you would draw starting from the first point to the second point. To make a linedef face the opposite way, you would flip the vertices.
Contents
Linedef structure[edit]
Doom level format[edit]
Each linedef is 14 bytes long.
Offset | Size in bytes | C99 type [doom 1] | Description |
---|---|---|---|
0 | 2 | int16_t | Start Vertex |
2 | 2 | int16_t | End Vertex |
4 | 2 | int16_t | Flags |
6 | 2 | int16_t | Special Type |
8 | 2 | int16_t | Sector Tag |
10 | 2 | int16_t | Front Sidedef [doom 2] |
12 | 2 | int16_t | Back Sidedef [doom 2] |
- ↑ The original source code uses type short. Most source ports and modern utilities change the interpretation of vertex and sidedef indices in this structure to be unsigned. This extends the limits on vertices and sidedefs from 32768 to 65535 items. Editors such as Doom Builder also often treat tag numbers and linedef special type as unsigned as well.
- ↑ 2.0 2.1 The special value -1 (hexadecimal 0xFFFF) is used to indicate no sidedef, in one-sided lines.
Doom 64 level format[edit]
The Doom 64 linedef is the same as the Doom format except for the Flags which are twice the size compared to Doom. Therefore each linedef is 16 bytes long.
Offset | Size in bytes | C99 type | Description |
---|---|---|---|
0 | 2 | int16_t | Start Vertex |
2 | 2 | int16_t | End Vertex |
4 | 4 | int32_t | Flags |
8 | 2 | int16_t | Special Type |
10 | 2 | int16_t | Sector Tag |
12 | 2 | int16_t | Front Sidedef |
14 | 2 | int16_t | Back Sidedef |
Hexen level format[edit]
Each linedef is 16 bytes long.
Offset | Size in bytes | C99 type [hexen 1] | Description |
---|---|---|---|
0 | 2 | int16_t | Start Vertex |
2 | 2 | int16_t | End Vertex |
4 | 2 | int16_t | Flags |
6 | 1 | uint8_t | Special Type |
7 | 1 | uint8_t | Argument 1 |
8 | 1 | uint8_t | Argument 2 |
9 | 1 | uint8_t | Argument 3 |
10 | 1 | uint8_t | Argument 4 |
11 | 1 | uint8_t | Argument 5 |
12 | 2 | int16_t | Front Sidedef [hexen 2] |
14 | 2 | int16_t | Back Sidedef [hexen 2] |
- ↑ The original source code uses types short and byte (an alias for unsigned char). Most source ports and modern utilities change the interpretation of vertex and sidedef indices in this structure to be unsigned. This extends the limits on vertices and sidedefs from 32768 to 65535 items.
- ↑ 2.0 2.1 The special value -1 (hexadecimal 0xFFFF) is used to indicate no sidedef, in one-sided lines.
Linedef flags[edit]
Linedefs contain a two-byte (16 bit) field reserved for various flags. Flags are as follows:
Doom level format[edit]
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 |
Strife level format[edit]
Strife made several additions to Doom's linedef flags:
Bit | Hex | Description |
---|---|---|
9 | 0x0200 | Jumpable railing |
10 | 0x0400 | Blocks floating monsters only |
11 | 0x0800 | 25% foreground / 75% background translucency |
12 | 0x1000 | 75% foreground / 25% background translucency |
Boom level format[edit]
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[edit]
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) |
See also[edit]
Sources[edit]
- Unofficial Doom Specs
- Boom source code: boomref.txt
- Doom 64 Tech Bible at Doomworld/idgames