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{{wrongtitle|title=phys_lengthconstraint}}
{{tabs|main=source|source=1|source2=1|phys_lengthconstraint}}
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{{CD|CPhysLength|file1=physconstraint.cpp|CPhysConstraint}}
{{this is a|point entity|name=phys_lengthconstraint}} It is a [[:Category:Constraints|constraint]] that restricts the maximum (and optionally minimum) distance two objects are allowed to be from each other. It is most often used to simulate [[move_rope|rope]], though it does not support the "stiffening" of rope attachment points that can be observed in reality; an object can rotate a full 360° in fact, clipping right through any rope that may be attached.


==Entity Description==
{{Important|The constraint is calculated not from the origin/mass centre of the attached entities, but from the entity's own origin and the location of its Hammer [[Hammer_View_Menu#Show_Helpers|helper]] (attachpoint). Be sure to place them appropriately or the game will crash!}}


A [[constraint]] between two physically simulated objects, specifying the distance they should keep from each other. By default the link behaves like an invisible [[move_rope|rope]], and allows the objects to draw closer together, but it can be made rigid with its second [[spawnflag]].
The constraint can be made rigid with its [[#Flags|second spawnflag]]. It then behaves much like a [[phys_ballsocket]], except that the objects can freely rotate around their ''own'' centres.


{{tip|This is the entity used to keep ropes under a certain length.}}
{{Official vmf example|sdk_phys_lengthconstraint.vmf}}


===Usage===
{{tip|To suspend a standard wooden crate and allow the player to break its constraint by pulling, use a force limit of 1350.}}


Lengthconstraint accepts two target entities:
== Keyvalues ==
{{KV Targetname}}
{{KV|Additional Length|intn=addlength|float|Elasticity of the constraint. It is allowed to stretch this many units over or under its maximum and minimum length. The constraint will try to spring back to its preferred length.}}
{{KV|Minimum Length|intn=minlength|float|Minimum distance between origin and attachpoint. Irrelevant if the constraint is rigid. Default is 0.}}
{{KV|Attached object 2 point|intn=attachpoint|vecline|The second end of the constraint (the other is the origin). The second attached entity will be [[phys_constraint|rigidly constrained]] to this location, and the first to the origin.}}
{{KV TwoObjectPhysics}}


*'''Entity 1 (<code>attach1</code>) is anchored to the [[origin]] of the lengthconstraint itself
== Flags ==
*'''Entity 2 (<code>attach2</code>) is anchored to the [[helper]]''' (<code>Attached object 2 point</code>)
{{Fl TwoObjectPhysics|Keep Rigid}}


If one of the attach [[keyvalue]]s is not specified, its respective end (i.e. the origin or the helper) will anchor to the [[world]] and never move.
== Inputs ==
{{I TwoObjectPhysics}}


{{warning|There is not currently any way to control the amount of movement at attachment points. This results in an unrealistic wobble when a constraint is stretched without breaking.}}
== Outputs ==
{{O TwoObjectPhysics}}


===Breaking===
[[Category:Constraints|L]]
 
The lengthconstraint can be made to break through [[I/O]] or with a combination of the '''<code>AddLength</code>''', '''<code>ForceLimit</code>''' and/or '''<code>TorqueLimit</code>''' keyvalues:
 
*'''<code>AddLength</code>''' allows the constraint to go a certain number of units over or under its normal length before any forces are applied.
*'''<code>ForceLimit</code>''' defines how much weight (in US pounds) can be put on a lengthconstraint before it breaks. 0 = infinite.
**As well as the weight of whatever is attached to it, the further a lengthconstraint is stretched beyond its initial length (plus or minus the value in <code>AddLength</code>), the more that gets applied.
**To hang a standard crate and allow the player to break its constraint by pulling, use a value of 1350.
*'''<code>[[wikipedia:torque|Torque]]Limit</code>''' defines the 'weight' of twist that the lengthconstraint can have applied before breaking  (in US pounds). 0 = infinite
**Confusingly, torque is '''NOT''' calculated along the axis of the constraint, only perpendicularly! You can spin a lengthconstraint as much as you like; it will not break.
 
{{tip|Always specify a breaking sound. The crunchier the better!}}
 
===See Also===
*[[move_rope]]
*[[Constraint]]
*SDK file: sourcesdk_content\hl2\mapsrc\sdk_phys_lengthconstraint.vmf
 
==Keyvalues==
* {{kv targetname}}
* '''attachpoint'''
:<[[vecline]]> Attached object 2 point - The position of the helper
* '''attach1'''
:<target_destination> Entity 1 - Entity that is anchored to the helper
* '''attach2'''
:<target_destination> Entity 2 - Entity that is anchored to the origin
* '''constraintsystem'''
:<target_destination> Constraint System Manager - The name of a [[phys_constraintsystem]] that this constraint should be a part of. All constraints on a set of entities should be placed in the same system, or they will fight each other during simulation.
* '''forcelimit'''
:<float> Force Limit to Break (lbs) - The amount of force an impact must apply to the constraint to break it. A way of calculating this is to set it to the mass of an object that would break this constraint if it were resting on the constrainted objects.
* '''torquelimit'''
:<float> Torque Limit to Break (lbs * distance)? - The amount of torque required to break the constraint. A way of calculating this is to multiply any reference mass by the resting distance (from the center of mass of the object) needed to break the constraint.
* '''breaksound'''
:Play Sound on Break - A sound played when the constraint is broken.
* '''addlength'''
:<float> Additional Length - Add (or subtract) this amount to the rest length of the rope.
* '''minlength'''
:<float> Minimum Length - If the constraint is not rigid, this is the minimum length it can be.
 
==Flags==
*1
: No Collision until break (default on)
*2
: Keep Rigid (default off)
 
==Inputs==
*{{i targetname}}
*'''Break'''
:Force the constraint to break
*'''TurnOn'''
:Enable the constraint.  Do this when the objects don't exist when the constraint spawns - or when you have deactivated the constraint.  Broken constraints can NOT be turned on.  They have been deleted.
*'''TurnOff'''
:Disable this constraint.
 
==Outputs==
* {{o targetname}}
*'''OnBreak'''
: Fired when this constraint breaks.

Latest revision as of 06:34, 29 April 2025

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C++ Class hierarchy
CPhysLength
↳CPhysConstraint
↳CLogicalEntity
↳CServerOnlyEntity
↳CBaseEntity
C++ physconstraint.cpp

phys_lengthconstraint is a point entity available in all Source Source games. It is a constraint that restricts the maximum (and optionally minimum) distance two objects are allowed to be from each other. It is most often used to simulate rope, though it does not support the "stiffening" of rope attachment points that can be observed in reality; an object can rotate a full 360° in fact, clipping right through any rope that may be attached.

Icon-Important.pngImportant:The constraint is calculated not from the origin/mass centre of the attached entities, but from the entity's own origin and the location of its Hammer helper (attachpoint). Be sure to place them appropriately or the game will crash!

The constraint can be made rigid with its second spawnflag. It then behaves much like a phys_ballsocket, except that the objects can freely rotate around their own centres.

PlacementTip.pngExample:See steamapps/common/sourcesdk_content/hl2/mapsrc/sdk_phys_lengthconstraint.vmf for example use (comes with Source SDK installation [confirm])
Tip.pngTip:To suspend a standard wooden crate and allow the player to break its constraint by pulling, use a force limit of 1350.

Keyvalues

Name (targetname) <string>[ Edit ]
The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g. parentname or target).
Also displayed in Hammer's 2D views and Entity Report.
See also:  Generic Keyvalues, Inputs and Outputs available to all entities

Additional Length (addlength) <float>
Elasticity of the constraint. It is allowed to stretch this many units over or under its maximum and minimum length. The constraint will try to spring back to its preferred length.
Minimum Length (minlength) <float>
Minimum distance between origin and attachpoint. Irrelevant if the constraint is rigid. Default is 0.
Attached object 2 point (attachpoint) <vector>
The second end of the constraint (the other is the origin). The second attached entity will be rigidly constrained to this location, and the first to the origin.

TwoObjectPhysics:

Entity 1 (attach1) <targetname>
Entity 2 (attach2) <targetname>
The entities to constrain. Leave one or the other field blank to constrain to the world.
Note.pngNote:Only one entity will be constrained, even if several share the given targetname.
Constraint System Manager (constraintsystem) <targetname>
A phys_constraintsystem that this constraint should be a part of. This avoids the "jiggling" caused by constraints applied to the same set of entities fighting with each other.
Force Limit to Break (forcelimit) <float>
Impact force required to break the constraint, in pounds. 0 means infinite. A way of calculating this is to set it to the weight of an object that would break the constraint if it were resting on its objects.
Torque Limit to Break (torquelimit) <float>
Torque required to break the constraint, in pounds*inches. 0 means infinite. A way of calculating this is to multiply any reference mass by the resting distance (from the center of mass of the object) needed to break the constraint.
Play Sound on Break (breaksound) <string>
A sound played when the constraint is broken.
Follow teleport distance (teleportfollowdistance) <float>
If one constrained object teleports more than this many units away, the other will teleport with it.


Flags

No Collision until break : [1]
Keep Rigid : [2]
Start inactive : [4]
Change mass to keep stable attachment to world : [8]
Do not connect entities until turned on : [16]

Inputs

TwoObjectPhysics:
Break
Force the constraint to break.
TurnOn
Enable the constraint; do this if the constrained objects don't exist when it spawns. Note that broken constraints cannot be turned back on as they have been deleted.
TurnOff
Disable the constraint.

Outputs

TwoObjectPhysics:
OnBreak
Fired when the constraint breaks.
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