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| {{langsp}} | | {{APH|Lag Compensation}} |
| : ''You may be looking for [[Latency Compensating Methods in Client/Server In-game Protocol Design and Optimization|Yahn Bernier's 2001 paper on game engine networking]].''
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| [[File:Lag compensation.jpg|thumb|Historic client hitboxes (red) versus rewound server hitboxes (blue).]]
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| '''Lag compensation''' is the notion of the server using a player's latency to rewind time when processing a [[usercmd]], in order to see what the player saw when the command was sent. In combination with [[prediction]], lag compensation can help to combat network latency to the point of almost eliminating it from the perspective of an attacker. For a more detailed explanation, see the [[Source Multiplayer Networking#Lag compensation|Source Multiplayer Networking]] article.
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| By default only players are rewound, and one second of location/animation history is kept.
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| {{note|{{ent|CBasePlayer}} does not use lag compensation; it must be implemented by a derived class. Valve's networked player classes do this already.}}
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| {{tip|Since {{l4d2}}, ''all'' entities can be lag compensated using the <code>LagCompensate</code> {{not in FGD}} keyvalue. Use this sparingly!}}
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| == Configuration ==
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| {{IO|cl_lagcompensation|param=bool|Allows clients to tell the server that they don't want their own commands lag compensated. This is ''not'' a cheat.}}
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| {{IO|cl_lagcomp_errorcheck|param=int|Deprecated? In theory displays error information for the given player index, in practice is not referenced anywhere.}}
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| {{IO|sv_lagcompensationforcerestore|param=bool|Cheat. Disabling this causes the game to check if each entity can still occupy its rewind position in the current, un-rewound world. If it can't, it is rewound to the last valid position instead of the desired one. {{todo|Why would anyone want that to happen?}}}}
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| {{IO|sv_showlagcompensation|param=bool|Cheat. Displays rewound [[hitbox]]es whenever a player is lag compensated. This fills the role of the old <code>sv_showhitboxes</code> command, only without the confusion caused by the hitboxes also being shown when compensation is not in effect.}}
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| Developer server builds (those compiled with <code>ALLOW_DEVELOPMENT_CVARS</code>), or by using server plugins such as [https://www.sourcemod.net/ SourceMod] have some extra commands:
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| {{IO|sv_unlag|param=bool|Enable/disable lag compensation entirely.}}
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| {{IO|sv_maxunlag|param=float|Number of seconds to store player positions for. Default (and maximum) is 1.}}
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| == Invocation ==
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| Simply wrap whatever code you want lag compensated within two calls to the <code>lagcompensation</code> object:
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| <source lang=cpp>
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| #ifdef GAME_DLL
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| #include "..\server\ilagcompensationmanager.h"
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| void CMyPlayer::FireBullets ( const FireBulletsInfo_t &info )
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| {
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| // Source 2007
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| lagcompensation->StartLagCompensation( this, this->GetCurrentCommand() );
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| // Alien Swarm and later (See also sub-section below)
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| lagcompensation->StartLagCompensation( this, LAG_COMPENSATE_HITBOXES );
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| BaseClass::FireBullets(info);
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| lagcompensation->FinishLagCompensation( this );
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| }
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| #endif
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| </source>
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| Time will be wound back on the call to <code>StartLagCompensation()</code>, and wound forward again on the call to <code>FinishLagCompensation()</code>.
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| == Lag Compensation Type ==
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| Starting with Alien Swarm, you can optimise lag compensation with these settings:
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| ; <code>LAG_COMPENSATE_BOUNDS</code>
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| : Rewind entities' locations only, skipping animations.
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| ; <code>LAG_COMPENSATE_HITBOXES</code>
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| : Rewind both locations and [[hitbox]]es. This is the standard setting.
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| ; <code>LAG_COMPENSATE_HITBOXES_ALONG_RAY</code>
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| : Rewind hitboxes if an entity is hit by a ray defined by the "weaponPos" <code>StartLagCompensation()</code> overload. Otherwise rewind bounds only.
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| These setting chosen applies to ''all'' entities affected by the rewind.
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| == Implementation ==
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| {{todo|Supporting lag compensation on new entities.}}
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| == See also ==
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| * [[Source Multiplayer Networking#Lag compensation]]
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| * [[NPC Lag Compensation]]
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| * [[Prediction]]
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| * [[Interpolation]]
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| [[Category:Networking]]
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Note:Archived rest of page history of page Lag Compensation
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