Weapons Programming - High-Level Overview Last edited 2 months ago2020-07-20 20:15:14 UTC

Half-Life Programming

One of the most common changes people want for their mod is to add new weapons to it, or make changes to existing weapons. This article attempts to be a high-level overview of the weapons system in the Half-Life SDK. This guide assumes that you have experience programming in C++, and a programming environment and your custom mod already set up.

This article specifically provides you with a guided tour around the Half-Life code base, with a focus on showing all the different areas that you will need to consider when modifying existing weapons or adding new ones.

The weapon class hierarchy

We'll start by looking at one weapon, to see what the class hierarchy looks like:
CCrowbar
└ CBasePlayerWeapon
  └ CBasePlayerItem
    └ CBaseAnimating
      └ CBaseDelay
        └ CBaseEntity
That's quite a few classes! Implementing your weapon will mostly involve overriding methods in several of these classes. Listing all the methods in each of these classes will take a long time (there's a lot), so we'll focus on those overridden by the weapons in the HL SDK only.
Note: in the tables below, the Implemented by sections list weapons that implement custom versions of the methods. If the method isn't implemented, the default implementation is used instead. CBasePlayerWeapon has some default implementations of methods in its parent class, and so on.

CBaseEntity

This is the base class for all entities. There are a lot of virtual methods on this class, but only a few need to be considered when working with weapons.
MethodDetails
PrecacheThis is used to preload sounds, models, and graphics required for the weapon. Implemented by: all weapons
SpawnThis is called when the map loads and will initialise everything required for the entity to function correctly in-game. For weapons, this typically means loading the weapon's model and anything else it needs. Implemented by: all weapons
SetObjectCollisionBoxThis is used to update the bounding box of the model, for pickup purposes. Aside from the tripmine, all weapons use the default bounding box. Implemented by: tripmine
Save & RestoreSave and Restore are key methods for all entities, and this is no different for weapons. If a weapon has custom fields that need to be persisted across saves, then both of these methods should be implemented. Notably, this is only implemented on the server DLL, not the client (using #ifndef CLIENT_DLL directives). Implemented by: shotgun, rpg, gauss, egon, satchel

CBasePlayerItem

This is the base class for "items" that the player has in their inventory that can be selected using the HUD and used by the player. However, in the final release of Half-Life, this only applies to weapons. Because of this, only CBasePlayerWeapon directly derives from this class. This class does, however, contain a lot of functionality relevant to weapons.
MethodDetails
AddToPlayerThis method is called when the weapon is added to the player, and the player doesn't already have the weapon in their inventory. Most weapons override this method in order to send a custom message to the client, so it can be displayed on the HUD. Implemented by: all weapons except for weapons that are their own ammo (crowbar, snarks, grenades and tripmines)
AddDuplicateThis method is called when the weapon is picked up by the player, but they already have the weapon in their inventory. Since this typically just adds extra ammo, it rarely needs to be changed. The satchel has special code to ensure that the number of thrown unexploded satchels are accounted for before allowing the additional ammo to be picked up. Implemented by: satchel
CanDeployThis method tests if a weapon can be selected using the HUD. The default implementation will return FALSE if the player has no ammo for the weapon. Satchels have a custom implementation so the player can select the detonator if there are unexploded satchels in the level. Implemented by: satchel
CanHolsterThis method tests if a weapon can be switched out by selecting a different weapon. In most cases, this is always TRUE. However, the RPG and grenade have custom code in order to prevent weapon changing while a rocket is in flight, or a grenade is primed. Implemented by: RPG, grenade
DeployThis function is called when the weapon should be "taken out" and equipped by the player. Implemented by: all weapons
GetItemInfoThis function is called to fetch information about the weapon such as name, ammo type, maximum clip sizes, and other properties. The data is sent to the client. All weapons should implement this method. Implemented by: all weapons
HolsterThis function is called when the weapon should be "put away", in order for a different one to be equipped. Implemented by: all weapons that have a custom "put away" animation
iItemSlotThis method returns the "slot" in the HUD that the weapon fits into. In the default HUD, the valid slot numbers are from 1 to 5. Implemented by: all weapons
SecondaryAmmoIndexThis method should be implemented if the secondary fire uses a different ammo type than the primary ammo type. In Half-Life, only the MP5 fits this category. Implemented by: MP5

CBasePlayerWeapon

This is the base class that all weapons inherit. Your custom weapon will almost certainly inherit directly from this class as well.
MethodDetails
IsUseableThis method determines if the weapon can be fired. By default, this will be FALSE if there is no ammo in the clip. Satchels have a custom implementation as the detonator can be fired even when the player has no satchel ammo. The hornet gun also has a custom implementation, as it recharges its own ammo automatically. Implemented by: satchel, hornet gun
PrimaryAttackThis method is called when the player presses the primary fire button (usually mouse1). Implemented by: all weapons
ReloadThis method is called when the player presses the reload button (usually R). Implemented by: weapons with a clip that can be reloaded - including the hornet gun, even though it "reloads" automatically
SecondaryAttackThis method is called when the player presses the secondary fire button (usually mouse2). Implemented by: all weapons with a secondary fire
ShouldWeaponIdleThis method should return TRUE if WeaponIdle should be called even if the weapon is being fired or reloaded. This is typically not what you want, however if you need to perform a particular operation every frame, it might be useful. The RPG uses this method to ensure the laser spot is continuously updated. Implemented by: RPG
WeaponIdleThis method is called after every frame, if the weapon is not firing or reloading. Typically, this is used to play idle animations for the weapons. Implemented by: weapons with an idle animation

Other weapon references

Aside from the main classes for weapons, weapons are referenced in several other areas of the code, as well as game resources. To fully set up a custom weapon, all of these must be considered in your changes.

Code: Weapon ID

If you open weapons.h, you'll find this block of code defining an ID for each weapon:
#define WEAPON_NONE          0
#define WEAPON_CROWBAR       1
#define WEAPON_GLOCK         2
#define WEAPON_PYTHON        3
#define WEAPON_MP5           4
#define WEAPON_CHAINGUN      5
#define WEAPON_CROSSBOW      6
#define WEAPON_SHOTGUN       7
#define WEAPON_RPG           8
#define WEAPON_GAUSS         9
#define WEAPON_EGON         10
#define WEAPON_HORNETGUN    11
#define WEAPON_HANDGRENADE  12
#define WEAPON_TRIPMINE     13
#define WEAPON_SATCHEL      14
#define WEAPON_SNARK        15
When adding a new weapon, simply add a new ID to this list of constants, incrementing the value. For example, the next new weapon would have an ID of 16. These constants are used in your weapon's code, in the Spawn method to set m_iId, and the GetItemInfo method to set the p->iId value. Refer to an existing weapon's implementation to see these in use - for example, the glock:
void CGlock::Spawn( )
{
    // code
    m_iId = WEAPON_GLOCK;
    // more code
}

int CGlock::GetItemInfo(ItemInfo *p)
{
    // code
    p->iId = m_iId = WEAPON_GLOCK;
    // more code
}

Code: Client side changes

Most of the "real work" with a weapon is done on the server - bullets are fired, ammo counts are changed, and damage is done. However, the client side also needs to do some work in order for a weapon to function correctly - typically, this is playing the "shoot" sound, applying bullet decals, ejecting empty shells, and similar audio-visual effects that the server doesn't particularly need to care about. Here's a quick rundown of what client code needs to be changed when programming with weapons.

If you search the rest of the code base for the ID constants (for example, WEAPON_GLOCK), you'll find only one other reference. It's in hl_weapons.cpp, in a method named HUD_WeaponsPostThink:
case WEAPON_GLOCK:
    pWeapon = &g_Glock;
    break;
This method is only run when client prediction is enabled (which it is, by default). You should add a new case for your weapon, just follow the same standard. Note that you'll also need to declare the equivalent of g_Glock for your weapon, as well as the HUD_PrepEntity call. All this code is in the hl_weapons.cpp file in the client project.

If you look at the code for existing weapons, you'll find lines that look like these:
// In the Precache method
m_usFirePython = PRECACHE_EVENT( 1, "events/python.sc" );

// In the PrimaryAttack (or similar) method
PLAYBACK_EVENT_FULL( flags, m_pPlayer->edict(), m_usFirePython, 0.0, (float *)&g_vecZero, (float *)&g_vecZero, vecDir.x, vecDir.y, 0, 0, 0, 0 );
You might like to investigate the events/python.sc file to see what's inside it. Don't bother! It's meaningless. The contents of the file is unimportant - and in the case of the stock HL weapons, they're all identical. Only the name of the file has any meaning. The contents of the file were probably intended to be some sort of scripting system for the engine, but it was never implemented. So just create an empty .sc file, or copy one of the existing ones, and give it a good name.

If you search for python.sc in the code, you'll only find it in two places. The first is in the weapon code, in the PRECACHE_EVENT call. The other is in hl_events.cpp, in a method called Game_HookEvents. If you look at the comments for Game_HookEvents, you can see a helpful explanation from a Valve programmer about why the contents of the .sc file isn't used.

Anyway, simply declare your event method in the extern "C" block at the top of this file, and then a gEngfuncs.pfnHookEvent call for your weapon/event inside Game_HookEvents. Next, grab one of those event function names, such as EV_FirePython, and do another search to see what you find.

Aside from the hl_events.cpp file you've just changed, the only other place these functions are found is the ev_hldm.cpp file. There's another extern "C" block to put the function definition in, and then the function implementations later on in the file. Your best bet is to copy an existing method and tweak it to suit your weapon.

Code: Weights (for auto-switching)

Back in weapons.h, you'll find another block of defines:
#define CROWBAR_WEIGHT      0
#define GLOCK_WEIGHT       10
#define PYTHON_WEIGHT      15
#define MP5_WEIGHT         15
#define SHOTGUN_WEIGHT     15
#define CROSSBOW_WEIGHT    10
#define RPG_WEIGHT         20
#define GAUSS_WEIGHT       20
#define EGON_WEIGHT        20
#define HORNETGUN_WEIGHT   10
#define HANDGRENADE_WEIGHT  5
#define SNARK_WEIGHT        5
#define SATCHEL_WEIGHT    -10
#define TRIPMINE_WEIGHT   -10
These constants are only typically used in the weapon's implementation, so they're somewhat optional and could instead be hard-coded into each weapon. It's convenient to keep them all in the same place, though, so it's best to add a new weight for your weapon as well.

Essentially, the weight defines if a weapon that has been picked up is "better" than the weapon that is currently equipped. If the weight is higher, the new weapon will be automatically equipped. Otherwise, it will be added to the player's inventory and they will have to switch to it themselves. The weight value is assigned to p->iWeight in the GetItemInfo method.

Code: Ammo constants

Still in weapons.h, after the weights you'll find 4 blocks of defines for ammo limits:
#define _9MM_MAX_CARRY       250
//
#define GLOCK_MAX_CLIP        17
//
#define GLOCK_DEFAULT_GIVE    17
//
#define AMMO_GLOCKCLIP_GIVE  GLOCK_MAX_CLIP
If you're adding a new ammo type, you should define a new MAX_CARRY constant. If you're adding a new ammo box type, you should define a new AMMO_GIVE constant. For new weapons, define both MAX_CLIP and DEFAULT_GIVE constants:

Code: Weapon precaching

In weapons.cpp, you'll find a function called W_Precache. This method will, as you might expect, precache the weapons when a level is loaded. Simply add lines for each new weapon (and ammo box) entity you add to your mod. For example, for the glock:
UTIL_PrecacheOtherWeapon( "weapon_9mmhandgun" );
UTIL_PrecacheOther( "ammo_9mmclip" );
Note that the value given to both UTIL_PrecacheOtherWeapon and UTIL_PrecacheOther is a class name. This is the class name as defined in the LINK_ENTITY_TO_CLASS line in your weapon code. If your weapon has multiple class names (e.g. the glock is both weapon_glock and weapon_9mmhandgun) it does not have to be precached twice. All these methods do is create an entity of that classname, call the Precache() method on it, and remove the entity.

Code: New ammo types

It's easiest to use the existing ammo types for your new weapons, but usually you'll probably want to add new types. This requires making a sequence of changes across multiple files. This will be covered in depth in the Custom Ammo Types article, but a quick summary would be:

Code: Ammo boxes

If you want to add a new ammo box, it's actually very simple. Just copy and paste an existing ammo box, and change the model, pickup sound, ammo types or numbers, and link it to a new class name. For full details, see the Zoomable Weapons article, which has a section on adding custom ammo types.

Code: Skill settings

Skill settings let your weapon do more (or less) damage based on the selected difficulty. If your weapon uses standard bullets, then your skill values should come from the ammo's skill values. But other weapons have their own custom skill values.

Skill cvars are defined game.cpp:
// Shotgun buckshot
cvar_t    sk_plr_buckshot1 = {"sk_plr_buckshot1","0"};
cvar_t    sk_plr_buckshot2 = {"sk_plr_buckshot2","0"};
cvar_t    sk_plr_buckshot3 = {"sk_plr_buckshot3","0"};
And they are registered in game.cpp, in the GameDLLInit method:
// Shotgun buckshot
CVAR_REGISTER ( &sk_plr_buckshot1 );// {"sk_plr_buckshot1","0"};
CVAR_REGISTER ( &sk_plr_buckshot2 );// {"sk_plr_buckshot2","0"};
CVAR_REGISTER ( &sk_plr_buckshot3 );// {"sk_plr_buckshot3","0"};
A variable for the value is present in the skilldata_t struct, in skill.h:
float plrDmgBuckshot;
Which is set in gamerules.cpp, in the RefreshSkillData method:
// Shotgun buckshot
gSkillData.plrDmgBuckshot = GetSkillCvar( "sk_plr_buckshot");
The GetSkillCvar method will select the value for 1, 2, or 3, based on whether the user has selected easy, medium, or hard (in that order) when they started the game.

These cvars have a default value of 0, so that needs to be changed. When the game starts, the skill.cfg file is loaded and the cvar values are read from them. The actual values for the skill cvars should be added to this file.
// Shotgun buckshot
sk_plr_buckshot1    "5"
sk_plr_buckshot2    "5"
sk_plr_buckshot3    "5"
For multiplayer games, the value is hard-coded so every player does the same amount of damage with every weapon. This is set in multiplay_gamerules.cpp, again in the RefreshSkillData method:
// Shotgun buckshot
gSkillData.plrDmgBuckshot = 20;
Finally, this value is referenced in the weapons code when dealing damage. For example, for the shotgun, the FireBulletsPlayer function is called, which has the following code:
case BULLET_PLAYER_BUCKSHOT:
    pEntity->TraceAttack(pevAttacker, gSkillData.plrDmgBuckshot, vecDir, &tr, DMG_BULLET);
    break;

Code: Impulse 101

Something that isn't always immediately obvious is that you want your weapon to be added when you run the impulse101 command in the console. Adding this is fairly straight forward if you know where to look - in player.cpp, find the CheatImpulseCommands function. towards the top of that function, you'll see a bunch of GiveNamedItem calls under the case 101: statement. Simply add another GiveNamedItem call with your weapon's classname, and you're good to go.

Code: func_breakable

Another option that might be forgotten about is allowing the weapon (and your new ammo, if applicable) to be placed inside a func_breakable entity. You can find the relevant code in func_break.cpp, near the top of the file. Add your desired classnames to the CBreakable::pSpawnObjects array, and you're done. Be sure to make the relevant changes to the FGD as well!

Resources: Weapon models and sounds

This should be obvious, but when you're adding a new model, you'll need new models and sounds. Weapons generally have two models:
  1. A lower-detail "world" model, which is what you see when the weapon is lying on the ground, prior to pickup.
  2. A higher-detail "view" model, which is what you see when the player is holding and shooting the weapon.
Aside from the actual modelling work, there are a few interesting features of the model's QC file that are especially relevant to weapons. If you look at a decompiled weapon's QC file, you might see some sequences defined like so:
$sequence "shoot" "shoot" fps 25 { event 5001 0 "11" }
$sequence "shoot_empty" "shoot_empty" fps 25 { event 5001 0 "11" }
$sequence "reload" "reload" fps 18 { event 5004 4 "items/9mmclip2.wav" } { event 5004 23 "items/9mmclip1.wav" }
$sequence "reload_noshot" "reload_noshot" fps 18 { event 5004 4 "items/9mmclip2.wav" } { event 5004 23 "items/9mmclip1.wav" }
The thing to note here is the event syntax. It looks like this:
{ event event_id frame_number event_options }
The engine will process the event when the indicated frame number is rendered by the engine. The options are passed as a string to the client to be handled. Events 5001 and 5004 are the main ones for most weapons, but you can see all of them defined in entity.cpp, in the HUD_StudioEvent function:
switch( event->event )
{
    case 5001:
        gEngfuncs.pEfxAPI->R_MuzzleFlash( (float *)&entity->attachment[0], atoi( event->options) );
        break;
    case 5011:
        gEngfuncs.pEfxAPI->R_MuzzleFlash( (float *)&entity->attachment[1], atoi( event->options) );
        break;
    case 5021:
        gEngfuncs.pEfxAPI->R_MuzzleFlash( (float *)&entity->attachment[2], atoi( event->options) );
        break;
    case 5031:
        gEngfuncs.pEfxAPI->R_MuzzleFlash( (float *)&entity->attachment[3], atoi( event->options) );
        break;
    case 5002:
        gEngfuncs.pEfxAPI->R_SparkEffect( (float *)&entity->attachment[0], atoi( event->options), -100, 100 );
        break;
    case 5004:
        gEngfuncs.pfnPlaySoundByNameAtLocation( (char *)event->options, 1.0, (float *)&entity->attachment[0] );
        break;
    default:
        break;
}
Essentially, events 5001, 5011, 5021, and 5031 will show a muzzleflash at weapon attachments 0, 1, 2, and 3 respectively. For the most part, you'll only ever have 1 attachment on a weapon, but some NPC models have more. Event 5002 is the same for a spark effect, but only for attachment 0. Event 5004 plays a sound - but only on the client side, other players won't hear it. This is why the "shoot" sound isn't a model event - other players need to be able to hear it.

Weapon sounds are fairly straight forward - you should have sounds for shooting, reloading, and so on. There's nothing special about them aside from the standard audio encoding settings that the engine needs.

Resources: HUD sprites

Setting up HUD sprites is a bit of a pain, because they're defined in "sprite sheets" inside the hud sprites. Each weapon has a text file inside the sprites folder which matches the weapon's entity name, as defined in pszName in the weapon's GetItemInfo function.

The text file has a relatively simple format. The first line is the number of lines in the file, not counting the first line. Subsequent lines are formatted like so:
type hud_size filename x y width height
A more detailed description of each field: For example, let's look at sprites/weapon_9mmhandgun.txt:
10
weapon        320 320hud1      0    40    80    20
weapon_s      320 320hud1      0    60    80    20
ammo          320 320hud2      0    16    18    18
crosshair     320 crosshairs   24    0    24    24
autoaim       320 crosshairs   0    72    24    24
weapon        640 640hud1      0    45    170   45
weapon_s      640 640hud4      0    45    170   45
ammo          640 640hud7      0    72    24    24
crosshair     640 crosshairs   24    0    24    24
autoaim       640 crosshairs   0    72    24    24
If you were to look inside these files, you would find the relevant icons for the pistol:
User posted image
User posted image

Resources: FGD definitions

The last thing to worry about when adding any new entities to the game is to modify the FGD so you can use it in your level editor. For weapons and ammo boxes, this is pretty simple - just copy an existing one and change the names. Weapons and ammo don't typically have any special keyvalues, so they'll be one-liners.
@PointClass base(Weapon, Targetx) studio("models/w_9mmhandgun.mdl") = weapon_9mmhandgun : "9mm Handgun" []
@PointClass base(Weapon, Targetx) studio("models/w_9mmclip.mdl") = ammo_9mmclip : "9mm Pistol Ammo" []

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