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{{LanguageBar|Generalities On Entities}}
[[Category:Programming]]
== Introduction ==
 
{{note|This article assumes that the reader has at least basic experience in C++}}
{{note|This article assumes that the reader has at least basic experience in C++}}


== Introduction ==
This article is mainly about entities in the Source engine and will try to explain everything about entities.
This article is mainly about entities in the Source engine and will try to explain everything about entities.


Every object, even the world, is an entity in the Source engine. All entities are derived from CBaseEntity.
Every object, even the world, is an entity in the Source engine. All entities are derived from CBaseEntity.


== Naming Conventions ==
== Naming conventions ==
In the Source engine, all class names begin with a capital <code>C</code>. Furthermore, on the client, the names begin with <code>C_</code> to differentiate them from their server counterparts.
 
Within the Source SDK, server classes begin with a capital C (<code>C</code>), while client classes begin with a capital C followed by an underscore (<code>C_</code>) - this helps differentiate between the two code bases.


For example:
For example:
Line 17: Line 16:
  Client: C_MyEntity
  Client: C_MyEntity


More information about these naming convention can be found at [[Wikipedia:Hungarian Notation|Hungarian Notation]]. Following this will save time later because classes and its variables will be easier to read.
The style of naming convention followed through the SDK code base is known as [[Wikipedia:Hungarian notation|Hungarian notation]]. Beginners are recommended to maintain the same style as used throughout the code base to save confusion.


== Which base class? ==
== Base classes ==
Every entity is based on <code>CBaseEntity</code>, however there are many derived classes. Here's a short list with the most famous ones:
Every entity is based on <code>CBaseEntity</code>, however there are many derived classes. The following is a list of the more common derived classes.


=== CBaseAnimating ===
=== [[CBaseAnimating]] ===
Every model that has a model uses CBaseAnimating. Classes derived from CBaseAnimating can set a model and animate.
Every entity that has a model uses CBaseAnimating. Classes derived from CBaseAnimating can set a model and animate.
{{note|Entities without models are not networked. A workaround is <code>AddEFlags( EFL_FORCE_CHECK_TRANSMIT );</code>}}
{{note|Entities without models are not networked by default. A workaround is <code>AddEFlags( EFL_FORCE_CHECK_TRANSMIT );</code>}}
{{note|To use animated models be sure to initialize the playback rate using SetPlaybackRate(1.0f); and call StudioFrameAdvance(); in the think function.}}


=== CBaseTrigger ===
=== [[CBaseTrigger]] ===
This entity is only used by mappers. Mappers need [[trigger|triggers]] for their maps.
[[trigger|Triggers]] are brush based entities that are generally placed during the map creation process.


=== CBasePlayer ===
=== [[CBasePlayer]] ===
This entity is the player itself. Every player-entity in the game is CBasePlayer or is derived from this entity.
This entity is the player itself. Every player-entity in the game is CBasePlayer or is derived from this entity.


=== CGameRules ===
=== [[CGameRules]] ===
This entity regulates the rules of the current game. It's mainly the gameplay.
This entity regulates the rules of the current game. It's mainly the gameplay.


=== CBaseCombatCharacter ===
=== [[CBaseCombatCharacter]] ===
Every NPC & player are derived from this class.
Every NPC & player are derived from this class.


== Think Functions ==
== Think functions ==
Think functions could be defined as Functions that dictate the behavior of an entity. They quite literally THINK for the function, and make it change states, and so on.
{{main|Think()}}
===Server side===
Think functions are a group of functions comprising the main way to have an entity act without input.  
====SetThink() and SetNextThink()====
An entity's Think() is run once after it spawns, and can be told when to call itself again using SetNextThink(). Using SetThink() can change between several Think() functions, and GetLastThink() returns the time of the last think function. See [[Think()]] for detailed description.
This assumes you know what a function pointer is. If you don't, go refresh your memory and come back when you have.
In setting up your entity, you will want for it to change, maybe change animations, or do something to players, or other entities... There's a host of things an entity can do, and I leave that up to you.
You can have many think functions, but here's another one of those hard-learned tips: '''THINK FUNCTIONS DO NOT EXIST ON THE CLIENT SIDE'''. At least not in the same manner that they do on the server.
Ok, let's get an example so you'll understand it more clearly:
I want to have an entity that does two things: When there is no player around, it will play it's idle animation, and do nothing more. When a player comes into range of it, it will start to emit puffs of smoke. So I will make two think functions: IdleThink and SmokeThink. These should return void and have no argument list like so:


void IdleThink(void);
== Macros ==
void SmokeThink(void);
Badly set up macros will give error messages, crash the game and cause erratic behavior. The following is a list of the more common macro definitions and some of the issues that surround them.


When the entity spawns, I will do this:
=== [[LINK_ENTITY_TO_CLASS]]() ===
This is one of the main macros. An entity cannot be created without this macro being used to define the entity's classname (as returned from <code>GetClassname()</code> on the server). However, on the client, an entity will not return its classname unless there is a matching data description (<code>DATADESC</code>).


SetThink( &CMyEntity::IdleThink );
=== [[PRECACHE_REGISTER]]() ===
SetNextThink( gpGlobals->curtime + 0.5 );
This is used to tell the engine that it needs to precache the entity when it loads. This is provided with the name of the entity (the same name as passed to [[LINK_ENTITY_TO_CLASS]]() ).


What this does is set this entity to run the IdleThink functions in 0.5 seconds.
=== [[DECLARE_CLASS]]() ===
Now in IdleThink, we will look for a player near us (Use a SphereQuery for example), if we find one, we will do:
This should be placed in the public section of an entity's Class definition. This provides access to the BaseClass Macro.


SetThink( &CMyEntity::SmokeThink );
=== DECLARE_[[DATADESC]](), BEGIN_[[DATADESC]](), END_[[DATADESC]](), and DEFINE_XXX() ===
SetNextThink(gpGlobals->curtime + 0.01);


If you tell SetNextThink that the next think time is '''almost''' now (when setting it to the current time, it may not always work) the function will get ran the next server frame. If we do not find a player near us, it is important that we still call SetNextThink:
The Data Description macros provide for a number of different features;
SetNextThink(gpGlobals->curtime);
* Specifying Think and Touch functions
* Providing Inputs and Outputs for mappers
* Providing external variable inputs (such as setting a model or the health of an item)


Otherwise, things will get messed up after that. I am not sure of the exact effect but I do believe that your entity will '''stop thinking''' if you do not set a new NextThink time.
Further information is available on the [[Data Descriptions]] page.


Right, this is all server side. Do not forget to use the [[DEFINE_THINKFUNC]] macro for all your think functions (we'll come back to that later as well).
=== Networking entities ===


===Client Side===
See the [[:Category:Programming#Networking|Networking]] section for more information on networking entities, as that is outside the scope of this article.
As I said before, the client does not have the same System for entities to think. These Client Thinks are handled in <code>client_thinklist.cpp</code>. You cannot define multiple think functions here, as SetThink will not work properly on this side. Instead, you must use the following:


====ClientThink() and SetNextClientThink()====
[[Category:Programming]]
These are the equivalent of the server system, except you only have one function at your disposal here (which sucks a bit for organization, but oh well). This will get called based on the SetNextClientThink() time you set in Spawn, and in subsequent calls to ClientThink(). You can use two special time settings here: [[CLIENT_THINK_ALWAYS]] and [[CLIENT_THINK_NEVER]].
 
====Simulate()====
Here's the commentary in c_baseentity.cpp: ''"Once-per-frame stuff should go in Simulate()."'' That really sums it up. I personally use Simulate() mainly for Particle effects, or graphical effects of any sorts. Beware of what you run in Simulate(), as said before, this gets run EVERY FRAME, meaning you should avoid creating 50 new particles every Frame ;)
 
That's about it I believe. Think functions are an essential part of any entity and you should learn to use them well.
 
== Macros ==
I want to dedicate an entire chapter to these Macros, because they are what causes problems with entities at least 60% of the time. Badly set up macros will give you errors messages, crash your game, give you erratic behavior, and so forth. I'm going to try to sum up most of them and a few more tips as best as I can:
 
===[[LINK_ENTITY_TO_CLASS]]()===
This is your main macro. You do not have an entity until you call this macro. This macro will NAME your entity for the game. Anytime you call GetClassname() on an entity, this is the name that will be returned on the server side. There is a subtlety however, which is that, on the client side, the entity name will not be the one you give to [[LINK_ENTITY_TO_CLASS]] unless you  make a DATADESC. Instead, it returns (client-side) something like "class C_MyEntity".
 
===[[PRECACHE_REGISTER]]()===
This is used to tell the engine that it needs to precache your entity when it loads. You pass it the name of your entity (the same you passed to [[LINK_ENTITY_TO_CLASS]]() ).
 
===[[DECLARE_CLASS]]()===
You need to put this in your Class definition, in a public section. This gives you access to the BaseClass Macro, which is very handy. I believe it also helps to set up some networking stuff.
 
===DECLARE_[[DATADESC]](), BEGIN_[[DATADESC]](), END_[[DATADESC]](), and DEFINE_XXX()===
This set of macros is used for two main things:
First, you need it if you're going to have think functions.
Second, I believe it takes care of saving any variable that is defined in the set for Single Player Games, and restoring their values when you load a saved game.
I refer you to the Valve tutorial [http://developer.valvesoftware.com/wiki/Data_Descriptions Data Descriptions] for more info.
 
===Networking Entities=== I was going to explain a little bit about networking entities and networked variables and such, but there are already a lot of nice tutorials by Valve that explain it all in detail. See the [[:Category:Programming#Networking|network section]] section in this wiki's [[:Category:Programming|programming category]].
 
== Conclusion ==
I have only brushed the surface here. I have been working with this SDK for over 8 months now, and I learn something new about it every time I open it. It is complex, it is vast, and you will not learn all about it by just reading tutorials. The best way to do it has always been for me to JUST DO IT. You take an idea, something you want to add to your MOD. You look around source with a few keywords to see what's already been done. You search on a few forums and see if it's already been discussed. You look at tutorial sites and see if anything relates to it. Once you have a good idea on how you're gonna do it, well you just dive in the deep end and start coding it!
 
I hope you've learned something from this tutorial. Once again, if I mislead you in anyway, it is not intentional. This is all of what I have learned through months of trial and error and I hope it speeds up your progress in learning more about this SDK.
 
Good Luck.
Imperio59

Latest revision as of 16:01, 18 July 2025

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Introduction

Note.pngNote:This article assumes that the reader has at least basic experience in C++

This article is mainly about entities in the Source engine and will try to explain everything about entities.

Every object, even the world, is an entity in the Source engine. All entities are derived from CBaseEntity.

Naming conventions

Within the Source SDK, server classes begin with a capital C (C), while client classes begin with a capital C followed by an underscore (C_) - this helps differentiate between the two code bases.

For example: 

Server: CMyEntity
Client: C_MyEntity

The style of naming convention followed through the SDK code base is known as Hungarian notation. Beginners are recommended to maintain the same style as used throughout the code base to save confusion.

Base classes

Every entity is based on CBaseEntity, however there are many derived classes. The following is a list of the more common derived classes.

CBaseAnimating

Every entity that has a model uses CBaseAnimating. Classes derived from CBaseAnimating can set a model and animate.

Note.pngNote:Entities without models are not networked by default. A workaround is AddEFlags( EFL_FORCE_CHECK_TRANSMIT );
Note.pngNote:To use animated models be sure to initialize the playback rate using SetPlaybackRate(1.0f); and call StudioFrameAdvance(); in the think function.

CBaseTrigger

Triggers are brush based entities that are generally placed during the map creation process.

CBasePlayer

This entity is the player itself. Every player-entity in the game is CBasePlayer or is derived from this entity.

CGameRules

This entity regulates the rules of the current game. It's mainly the gameplay.

CBaseCombatCharacter

Every NPC & player are derived from this class.

Think functions

Main article:  Think()

Think functions are a group of functions comprising the main way to have an entity act without input. An entity's Think() is run once after it spawns, and can be told when to call itself again using SetNextThink(). Using SetThink() can change between several Think() functions, and GetLastThink() returns the time of the last think function. See Think() for detailed description.

Macros

Badly set up macros will give error messages, crash the game and cause erratic behavior. The following is a list of the more common macro definitions and some of the issues that surround them.

LINK_ENTITY_TO_CLASS()

This is one of the main macros. An entity cannot be created without this macro being used to define the entity's classname (as returned from GetClassname() on the server). However, on the client, an entity will not return its classname unless there is a matching data description (DATADESC).

PRECACHE_REGISTER()

This is used to tell the engine that it needs to precache the entity when it loads. This is provided with the name of the entity (the same name as passed to LINK_ENTITY_TO_CLASS() ).

DECLARE_CLASS()

This should be placed in the public section of an entity's Class definition. This provides access to the BaseClass Macro.

DECLARE_DATADESC(), BEGIN_DATADESC(), END_DATADESC(), and DEFINE_XXX()

The Data Description macros provide for a number of different features;

  • Specifying Think and Touch functions
  • Providing Inputs and Outputs for mappers
  • Providing external variable inputs (such as setting a model or the health of an item)

Further information is available on the Data Descriptions page.

Networking entities

See the Networking section for more information on networking entities, as that is outside the scope of this article.

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