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2015-07-28T21:27:41Z

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{{DoomWiki}}'''Linedefs''' are what make up the 'shape' (for lack of a better word) of a map. Every linedef is between two [[vertex|vertices]] and contains one or two [[sidedef]]s (which contain [[wall texture]] data). There are two major purposes of linedefs. The first is to divide the map into [[sector]]s, 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 <tt>idclip</tt> [[Doom cheat codes|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).

==Linedef structure==
{{Doom level format}}

Each linedef is 14 bytes long.

===Doom level format===

{| {{prettytable}}

! Offset !! Size (bytes) !! Description
|-
| align="center" | 0 || align="center" | 2 || Start Vertex
|-
| align="center" | 2 || align="center" | 2 || End Vertex
|-
| align="center" | 4 || align="center" | 2 || Flags
|-
| align="center" | 6 || align="center" | 2 || Special Type
|-
| align="center" | 8 || align="center" | 2 || Sector Tag
|-
| align="center" | 10 || align="center" | 2 || Right Sidedef {{ref|1}}
|-
| align="center" | 12 || align="center" | 2 || Left Sidedef {{ref|1}}
|}

{{note|1}} The special value '-1' is used to indicate no sidedef, in one-sided lines.

===Hexen level format ===
{| {{prettytable}}

! Offset !! Size (bytes) !! Description
|-
| align="center" | 0 || align="center" | 2 || Start Vertex
|-
| align="center" | 2 || align="center" | 2 || End Vertex
|-
| align="center" | 4 || align="center" | 2 || Flags
|-
| align="center" | 6 || align="center" | 1 || [[Hexen action specials|Special Type]]
|-
| align="center" | 7 || align="center" | 1 || Argument 1
|-
| align="center" | 8 || align="center" | 1 || Argument 2
|-
| align="center" | 9 || align="center" | 1 || Argument 3
|-
| align="center" | 10 || align="center" | 1 || Argument 4
|-
| align="center" | 11 || align="center" | 1 || Argument 5
|-
| align="center" | 12 || align="center" | 2 || Right Sidedef
|-
| align="center" | 14 || align="center" | 2 || Left Sidedef
|}

==Linedef flags==

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

===Doom level format===
{| {{prettytable}}

!Bit
!Hex
!Description

|-
|0
|0x0001
|blocks [[player]]s and [[monster]]s

|-
|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:
{| {{prettytable}}

!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:
{| {{prettytable}}

!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)

|-
|}

[[Category:Doom_engine]]
[[Category:WAD lumps]]
[[Category:Lists]]

Linedef - Revision history

Corbin: Created page with "{{DoomWiki}}'''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 sided..."