2. Triggerable Linedef Types

2.1 Triggers

A linedef trigger is always activated in one of three ways - pushing on the first sidedef of the linedef, walking over the linedef, or shooting the linedef with an impact weapon (fists, chainsaw, pistol, shotgun, double barreled, or chaingun).

Linedefs activated by pushing on them come in two varieties. A manual linedef affects the sector on the second sidedef of the line pushed. A switched linedef affects all sectors that have the same tag field as the linedef that was pushed.

Nearly all switched, walkover, and gun linedefs operate on the sectors with the same tag as that in the tag field of the linedef.

Some linedefs are never activated per se, but simply create or control an effect through their existence and properties, usually affecting the sectors sharing the linedef's tags. There are also a few special case like line-line teleporters and exit linedefs that do not affect sectors.

Some linedefs are only triggerable once, others are triggerable as many times as you like.

Triggering types are denoted by the letters P, S, W, and G for manual(push), switched, walkover, and gun resectively. Their retriggerability is denoted by a 1 or R following the letter. So the triggering types for linedefs are: P1 PR S1 SR W1 WR G1 GR

Other documents on Doom editing, and many Doom editors, follow the same or a similar convention. The main variation that you may see is D1 and DR instead of P1 and PR (D for "Door", because this is the most common use of such lines - the Boom editing reference also incorrectly used these abbreviations in several places, when they meant P1, PR).

Often linedef actions depend on values in neighboring sectors. A neighboring sector is one that shares a linedef in common, just sharing a vertex is not sufficient.

In DOOM only one action on a sector could occur at a time. PrBoom supports one floor action, one ceiling action, and one lighting action simultaneously.

2.2 Doors

A door is a sector, usually placed between two rooms, whose ceiling raises to open, and lowers to close. A door is fully closed when its ceiling height is equal to its floor height. A door is fully open when its ceiling height is 4 less than the lowest neighbor ceiling adjacent to it.

A door may be set to an intermediate state initially, or thru the action of a linedef trigger that affects ceilings or floors. In general the door is passable to a monster or a thing when its ceiling is at least the monster or thing's height above the floor.

If a door has a ceiling height ABOVE the fully open height, then an open door action moves the ceiling to the fully open height instantly. If a door has a ceiling height BELOW the fully closed height (that is the ceiling of the door sector is lower than the floor of the door sector) a close door action moves the ceiling to the fully closed height instantly.

There are 4 styles of door mechanism:

Open, Wait, Then Close

On activation, door opens fully, waits a specified period, then closes fully.

Open and Stay Open

On activation, door opens fully and remains there.

Close and Stay Closed

On activation, door closes fully, and remains there.

Close, Wait, Then Open

On activation, door closes fully, waits a specified period, then opens fully.

In the tables below, we denote these four mechanisms by odc, o, c, cdo respectively.

A door can be triggered by pushing on it, walking over or pressing a linedef trigger tagged to it, or shooting a linedef tagged to it. These are called manual, walkover, switched, or gun doors resp.

Each door trigger can also have a number of other properties:

• It can be locked. This means that the door trigger will only operate if the player is in possession of the right key(s). Regular and extended door triggers only care if the player has a key of the right color, they do not care which. Door triggers can distinguish between skull and card keys, and can also require any key, or all keys in order to activate.
• Speed: slow, normal, fast or turbo. Each step of the scale represents a doubling of speed.
• For door triggers with a wait, the amount of time can vary.
• It may or may not be activatable by monsters.

Calculating Generalised Door Types

There are two generalised linedef types for doors.

Line types between 0x3c00 and 0x4000 are simple doors. Within this range, the exact value determines the properties of the door; these are the fields:

Line types between 0x3800 and 0x3c00 are locked doors. Within this range, the exact value determines the properties of the door; these are the fields:

Note that only the open door types are available for locked doors, and that monsters can never open them.

rc = red card, bc = blue card, ys = yellow skull etc. "any" and "all" mean that any key or all the keys, respectively, are needed to unlock. If the "sk=ck" field is set to 1, then the distinction between skull and card keys is dropped; it is effectively assumed that if you have one key, you have all keys of that colour.

Misc

Any door function except Close and Stay Closed, when closing and encountering a monster or player's head will bounce harmlessly off that head and return to fully open. A Close and Stay Closed will rest on the head until it leaves the door sector.

Since a push door (P1/PR) has no use for its tag (since it always affects only the sector on its second sidedef), BOOM and MBF have used its tag for another purpose. In PrBoom, when a push door is opened or closed, any sectors tagged to the pushed linedef will have their lighting adjusted as the door moves. When the door is fully open, they will be set to maximum neighbor lighting; when fully closed, to minimum neighbor lighting. When partly open, their light level should be set in between. The idea is that as a door opens, such tagged sectors should change light level smoothly.

Note that this behavior is in common with MBF, but is different from BOOM and possibly other ports supporting BOOM's linedef extensions. There is a compatibility flag in MBF and PrBoom which emulated BOOM's behavior. It is not possible to set this flag from a PWAD in PrBoom.

2.3 Floors

This section covers line types which cause simple floor movements - the floor moves from its old height to a new height, either instantaneously, or moving at a steady speed. There are various properties which a floor movement has:

• The most complex aspect of moving floors in Doom is setting the target floor height. All of Doom's floor trigger types specify floor heights relative either to the sector's current height, or relative to its neighbours.
• Each floor linedef type has a direction.
• A speed. Ignored in the case of instantaneous jumps as described later.
• It can specify that a texture change should also occur, and can also change the sector type (for example, to change whether a sector is acid).
• It can be crushing; solid objects which would prevent it rising are instead crushed.

If a floor moving toward its destination height encounters an obstacle, it waits until the obstacle is removed (unless the obstacle is crushable and the floor is crushing).

Floor Targets

There are various ways of choosing the target floor level. These are listed below; first, some generalities.

Two sectors are considered neighbours if they share a linedef (i.e. the linedef has two sidedefs, one in each sector).

Some target types don't depend on the direction. In these cases, if the direction is "wrong", i.e. the new floor level is in the opposite direction to that specified, then the floor moves instantaneously to the target level. In this case, the normal speed of the trigger is ignored, and I think no crushing is performed and no obstacles are considered. I should check.

Most of the target types either implicitely or explicitely depend on their direction, so the direction is never "wrong", and they always move at the specified speed (not instantaneously).

After each target type, I give a short mneumonic for it in brackets, which is used in the tables later.

Lowest Neighbor Floor (LnF)

This means that the floor moves to the height of the lowest neighboring floor including the floor itself.

Next Neighbor Floor (NnF)

This means that the floor moves up to the height of the lowest adjacent floor greater in height than the current, or down to the height of the highest adjacent floor less in height than the current, as determined by the floor's direction.

Lowest Neighbor Ceiling (LnC)

This means that the floor height changes to the height of the lowest ceiling possessed by any neighboring sector, including that floor's ceiling.

8 Under Lowest Neighbor Ceiling (8uLnC)

This means that the floor height changes to 8 less than the height of the lowest ceiling possessed by any neighboring sector, including that floor's ceiling.

Highest Neighbor Floor (HnF)

This means that the floor height changes to the height of the highest neighboring floor, excluding the floor itself. If no neighbor floor exists, the floor moves down to -32000.

8 Above Highest Neighbor Floor (8aHnF)

This means that the floor height changes to 8 above the height of the highest neighboring floor, excluding the floor itself. If no neighbor floor exists, the floor moves down to -31992.

Ceiling

The floor moves up until its at ceiling height, instantly if floor direction is down.

24 Units (24)

The floor moves 24 units in the floor action's direction.

32 Units (32)

The floor moves 32 units in the floor action's direction.

512 Units (512)

The floor moves 512 units in the floor action's direction.

Shortest Lower Texture (SLT)

The floor moves the height of the shortest lower texture on the boundary of the sector, in the floor direction. In the case that there is no surrounding texture the motion is to -32000 or +32000 depending on direction.

None

Some pure texture type changes are provided for changing the floor texture and/or sector type without moving the floor.

Texture/Sector changing

A floor action can be a texture change type, in which case after the action the floor texture of the affected floor, and possibly the sector type of the affected floor, are changed, to those of a model sector. The sector type may be zeroed instead of copied from the model, or not changed at all. These change types are referred to below as Tx (texture only), Tx0 (type zeroed), and TxTy (texture and type changed).

There are two ways of choosing the model sector:

• The trigger model (Trg) - the sector on the 1st side of the trigger line is used.
• The numeric model (Num) - the lowest numbered linedef in the sector whose other side is at the destination height of this movement is found, and the sector on that other side is used as the model.

To clarify, these are the steps used by the numeric model:

• Find all floors adjacent to the tagged floor at destination height
• Find the lowest numbered linedef separating those floors from that tagged
• The sector on the other side of that linedef is the model

Calculating Generalized Floor Types

Line types between 0x6000 and 0x8000 are floor types. Within this range, the exact value determines the properties of the floor trigger; these are the fields:

When change is nochg, model is 1 when monsters can activate the line, otherwise monsters cannot activate it. When change is not nochg, the model field determined the method of determining the model sector.

2.4 Ceilings

This section covers line types which cause simple ceiling movements - the floor moves from its old height to a new height, either instantaneously, or moving at a steady speed. There are various properties which a ceiling movement has:

• The most complex aspect of moving ceilings in Doom is setting the target floor height. All of Doom's ceiling trigger types specify heights relative either to the sector's current ceiling height, or relative to its neighbours.
• Each type has a direction.
• A speed. Ignored in the case of instantaneous jumps.
• It can specify that a texture change should also occur, and can also change the sector type (for example, to change whether a sector is acid).
• It can be crushing; solid objects which would prevent it rising are instead crushed.

If a floor moving toward its destination height encounters an obstacle, it waits until the obstacle is removed (unless the obstacle is crushable and the floor is crushing).

Ceiling Targets

There are various ways of choosing the target ceiling height. These are listed below; first, some generalities, the same as for floors.

Two sectors are considered neighbours if they share a linedef (i.e. the linedef has two sidedefs, one in each sector).

Some target types don't depend on the direction. In these cases, if the direction is "wrong", i.e. the new ceiling level is in the opposite direction to that specified, then the ceiling moves instantaneously to the target level. In this case, the normal speed of the trigger is ignored, and I think no crushing is performed and no obstacles are considered. I should check.

Most of the target types either implicitely or explicitely depend on their direction, so the direction is never "wrong", and they always move at the specified speed (not instantaneously).

After each target type, I give a short mneumonic for it in brackets, which is used in the tables later.

Next Neighbor Ceiling (NnC)

This means that the ceiling moves up to the height of the lowest adjacent ceiling greater in height than the current, or to the height of the highest adjacent ceiling less in height than the current, as determined by the ceiling's direction. If no such ceiling exists, the ceiling does not move.

Lowest Neighbor Ceiling (LnC)

This means that the ceiling height changes to the height of the lowest ceiling possessed by any neighboring sector, NOT including itself. If no adjacent ceiling exists the ceiling moves to 32000 units.

Highest Neighbor Floor (HnF)

This means that the ceiling height changes to the height of the highest neighboring floor, excluding the ceiling's floor itself. If no neighbor floor exists, the ceiling moves down to -32000 or the ceiling's floor, whichever is higher.

Floor

The ceiling moves down until its at floor height.

8 Above Floor (8aF)

This means that the ceiling height changes to 8 above the height of the ceiling's floor.

24 Units (24)

The ceiling moves 24 units in the ceiling action's direction.

32 Units (32)

The ceiling moves 32 units in the ceiling action's direction.

Shortest Upper Texture (SUT)

The ceiling moves the height of the shortest upper texture on the boundary of the sector, in the ceiling direction. In the case that there is no surrounding texture the motion is to -32000 or +32000 depending on direction.

Texture/Sector changing

A ceiling action can be a texture change type, in which case after the action the ceiling texture of the affected ceiling, and possibly the sector type of the affected sector, are changed to those of a model sector. The sector type may be zeroed instead of copied from the model, or not changed at all. These change types are referred to below as Tx (texture only), Tx0 (type set to 0), and TxTy (texture and type copied from model).

There are two ways of choosing the model sector:

• The trigger model (Trg) - the sector on the 1st side of the trigger line is used.
• The numeric model (Num) - the lowest numbered linedef in the sector whose other side has ceiling at the destination height of this movement is found, and the sector on that other side is used as the model.

To clarify, these are the steps used by the numeric model:

• Find all ceilings adjacent to the tagged ceiling at destination height
• Find the lowest numbered linedef separating those ceilings from that tagged
• The sector on the other side of that linedef is the model

Calculating Generalized Ceiling Types

Line types between 0x4000 and 0x6000 are floor types. Within this range, the exact value determines the properties of the floor trigger; these are the fields:

When change is nochg, model is 1 when monsters can activate the line, otherwise monsters cannot activate it. When change is not nochg, the model field determined the method of determining the model sector.

2.5 Platforms (Lifts)

A platform is basically a floor action involving two heights. The simple raise platform actions, for example, differ from the corresponding floor actions in that if they encounter an obstacle, they reverse direction and return to their former height.

The most often used kind of platform is a lift which travels from its current height to the target height, then waits a specified time and returns to it former height.

Platform Targets

Lowest Neighbor Floor

This means that the platforms "low" height is the height of the lowest surrounding floor, including the platform itself. The "high" height is the original height of the floor.

Next Lowest Neighbor Floor

This means that the platforms "low" height is the height of the highest surrounding floor lower than the floor itself. If no lower floor exists, no motion occurs as the "low" and "high" heights are then both equal to the floors current height.

Lowest Neighbor Ceiling

This means that the platforms "low" height is the height of the lowest surrounding ceiling unless this is higher than the floor itself. If no adjacent ceiling exists, or is higher than the floor no motion occurs as the "low" and "high" heights are then both equal to the floors current height.

Lowest and Highest Floor

This target sets the "low" height to the lowest neighboring floor, including the floor itself, and the "high" height to the highest neighboring floor, including the floor itself. When this target is used the floor moves perpetually between the two heights. Once triggered this type of linedef runs permanently, even if the motion is temporarily suspended with a Stop type. No other floor action can be commanded on the sector after this type is begun.

Ceiling

This target sets the "high" height to the ceiling of the sector and the "low" height to the floor height of the sector and is only used in the instant toggle type that switches the floor between the ceiling and its original height on each activation. This is also the ONLY instant platform type. There are just two extended line numbers which provide this type, 211 (SR - repeatable switch) and 212 (WR - repeatable walk trigger).

Raise Next Floor

This means that the "high" height is the lowest surrounding floor higher than the platform. If no higher adjacent floor exists no motion will occur.

Raise 24 Units

The "low" height is the original floor height, the "high" height is 24 more.

Raise 32 Units

The "low" height is the original floor height, the "high" height is 32 more.

Properties of Platforms

• A speed
• The delay between stages of the platform's movement (e.g. the wait at the bottom of a lift's motion before it rises again, or the delay at each end of a perpetually moving floor's motion).
• A texture change. See the discussion on floor texture changers earlier, eith the exception that the model sector is always the sector on the first sidedef of the trigger (the trigger model as described earlier).

Calculating Generalized Platform Types

Line types between 0x3400 and 0x3800 are platform types. Within this range, the exact value determines the properties of the crusher trigger; these are the fields:

Other Platform line types

There are 4 line types provided which stop currently moving platforms:

There are just a small number of testure change platform types available, as regular and extended line types. They are all slow, not triggerable by monsters, with 0 delay. They are:

2.6 Crushers

A crusher ceiling is a linedef type that causes the ceiling to cycle between its starting height and 8 above the floor, damaging monsters and players that happen to be in between. Barrels explode when crushed.

A crusher has a speed: slow, normal, fast, or turbo. The slower the speed, the more damage the crusher does when crushing, simply thru being applied longer. When a slow or normal crusher is moving down and encounters something to crush, it slows down even more, by a factor of 8. This persists until it reaches bottom of stroke and starts up again. Fast and turbo crushers do not slow down.

A crusher can be silent. The regular silent crusher makes platform stop and start noises at top and bottom of stroke. The generalized silent crusher is completely quiet.

Calculating Generalized Crusher Types

Line types between 0x2f80 and 0x3000 are crusher types. Within this range, the exact value determines the properties of the crusher trigger; these are the fields:

Stopping crushers

Once a crusher ceiling is started it remains running for the remainder of the level even if temporarily suspended with a stop type. No other ceiling action can be used in that sector thereafter.

Four linedefs are provided to stop a crusher in its current position. Care should be used that this doesn't lock the player out of an area of the wad if the crusher is too low to pass. A crusher can be restarted, but not changed, with any crusher linedef. The four types are:

2.7 Stair Builders

A stair builder is a linedef type that sets a sequence of sectors defined by a complex rule to an ascending or descending sequence of heights.

The rule for stair building is as follows:

1. The first step to rise or fall is the tagged sector. It rises or falls by the stair stepsize, at the stair speed, in the stair direction..
2. To find the next step (sector) affected examine each two-sided linedef with first sidedef facing into the previous step in numerical order. For each such linedef if the sector on the other side is already active, or has already risen from this stair, the linedef is skipped. If textures are not ignored then any linedef with a different floor texture on its second side is also skipped. The next step to rise is the sector on the other side of the first linedef not skipped. If none exists, stair building ceases.
3. The next step moves to the height of the previous step plus or minus the stepsize depending on the direction the stairs build, up or down. If the motion is in the same direction as the stairs build, it occurs at stair build speed, otherwise it is instant.
4. Repeat step 2 until stair building ceases.

Stair builder properties

• Can build up or down.
• A step size of 4, 8, 16, or 24.
• A build speed
• A stair can stop on encountering a different texture (the traditional behavior) or ignore different textures and continue.

As a special exception to normal rules, the generalized retriggerable stairs alternate building up and down on each activation, which is much more useful than the default behaviour would be.

Only the regular build fast, stepsize 16 stair has the property that monsters and players can be crushed by the motion, all others do not crush.

Calculating Generalized Stair Types

Line types between 0x3000 and 0x3400 are stair types. Within this range, the exact value determines the properties of the stair trigger; these are the fields:

2.8 Lighting

The lighting linedef types change the lighting in the tagged sector. All are regular or extended types, there are no generalized lighting types. All are switched or walkovers.

Lighting Targets

Lights to Minimum Neighbor

Each tagged sector is set to the minimum light level found in any adjacent sector. The tagged sectors are changed in numerical order, and this may influence the result.

Lights to Maximum Neighbor

Each tagged sector is set to the maximum light level found in any adjacent sector. The tagged sectors are changed in numerical order, and this may influence the result.

Blinking

Each tagged sector begins blinking between two light levels. The brighter level is the light level in the tagged sector. The darker level is the minimum neighbor light level, or 0 if all neighbor sectors have lighting greater than or equal to the sector's at the time of activation. The blinking is non-synchronous, beginning 1-9 gametics after activation, with a dark period of 1 sec (35 gametics) and a bright period of 1/7 sec (5 gametics).

35 Units

Each tagged sector is set to a light level of 35 units.

255 Units

Each tagged sector is set to a light level of 255 units.

Lighting Linedef Types

2.9 Elevators

An elevator is a linedef type that moves both floor and ceiling together. All elevator linedefs are extended, there are no regular or generalized elevator types. Instant elevator motion is not possible, and monsters cannot activate elevators. All elevator triggers are either switched or walkover.

Elevator Targets

Next Highest Floor

The elevator floor moves to the lowest adjacent floor higher than the elevator's floor, the ceiling staying the same height above the floor. If there is no higher floor the elevator doesn't move.

Next Lowest Floor

The elevator floor moves to the highest adjacent floor lower than the current floor, the ceiling staying the same height above the floor. If there is no lower floor the elevator doesn't move.

Current Floor

The elevator floor moves to the height of the floor on the first sidedef of the triggering line, the ceiling remaining the same height above the elevator floor.

Elevator Linedef Types

2.10 Old Line Types

This section lists the old, traditional Doom and Boom linedef types for various actions. There is no rhyme nor reason to these numbers, this is just how they are. We're stuck with them for backward compatibility purposes, and because most level editors still use them. If you want to do clever stuff with lines yourself, don't use these - the only reason to use these in levels is for doom2.exe compatibility, or because your editor provides an easy interface for choosing from them.

See the preceeding sections for descriptions of how these work. Hopefully everything is self explanatory.

Doors

Floors

Ceilings

Platforms

All these obsolete platform types do no texture change, and cannot be triggered by monsters.