Flag

A Flag (bitmask or mask) is a boolean value that is stored within a large variable. This is advantageous because the smallest amount of memory that a program can allocate is 1 byte (or 8 bits), but a boolean only strictly needs 1 bit. If you have a lot of booleans to store, flags are eight times more efficient than the dedicated bool type.

Entities in Source commonly use the following flag types:

• Spawn flags - SF_ defined in each entity's .cpp file
• Behavior flags - FL_ flags defined in public/const.h
• Effect flags - EF_ flags defined in public/const.h
• Entity flags (aka EFlags) - EFL_ flags defined in game/shared/shareddefs.h

Brushes use the following flag types:

• Contents flags - CONTENTS_ flags defined in public/bspflags.h
• Surface flags - SURF_ flags defined in public/bspflags.h

Usage

Flags should be managed through Source's dedicated functions, never directly. There are several different types of flags and each has its own set of functions, but they all follow the same naming pattern:

• Add<*>Flags()
• Remove<*>Flags()
• Clear<*>Flags()
• Has<*>Flags() (sometimes Is<*>FlagSet())

These are the functions to call for common flag types:

	Prefix	Add	Remove	Check	Clear	Get All	Internal Field
Spawn Flags	SF_	AddSpawnFlags	RemoveSpawnFlags	HasSpawnFlags	ClearSpawnFlags	GetSpawnFlags	m_spawnflags
Behavior Flags	FL_	AddFlag	RemoveFlag	N/A	ClearFlags	GetFlags	m_fFlags
Effect Flags	EF_	AddEffects	RemoveEffects	IsEffectActive	ClearEffects	GetEffects	m_fEffects
Entity flags	EFL_	AddEFlags	RemoveEFlags	IsEFlagSet	N/A	GetEFlags	m_iEFlags

Warning:Don't modify the fields in the Internal Field column directly; always call the functions to add or remove flags, as many of the functions do additional work to notify the entity system that the entity's state has changed.

Note:Make sure you always use the right functions for the right type of flags, as the compiler won't detect if you've made a mistake. It's very easy to mix up flags starting with EFL_ and EF_, so always double check. Some of Valve's own code makes these mistakes!

To operate on several flags at once you must use the bitwise operators &, | and ^ - the same as the normal boolean operators, but with only one character.

For instance:

if ( HasSpawnFlags(SF_CITIZEN_MEDIC | SF_CITIZEN_NOT_COMMANDABLE) )
	...

Creation

Flags are typically defined as an enum like this:

enum MyFlags_t
{
    FL_MYFLAG = 1 << 0,
    FL_MYFLAG = 1 << 1,
    FL_MYFLAG = 1 << 2,
    // etc.
};

This is the same as:

enum MyFlags_t
{
    FL_MYFLAG = 1,
    FL_MYFLAG = 2,
    FL_MYFLAG = 4,
    // etc.
};

Or:

enum MyFlags_t
{
    FL_MYFLAG = 0x1,
    FL_MYFLAG = 0x2,
    FL_MYFLAG = 0x4,
    // etc.
};

Older code uses the preprocessor to define flags, although this should be avoided as it is not strongly typed:

#define FL_MYFLAG 1<<0
#define FL_MYFLAG 2
#define FL_MYFLAG 0x4
// etc.

Flags in Hammer

Flags appear in object properties in Valve Hammer Editor. Different objects will have different flags available. A flag appears as a checkbox, meaning each flag can be either on or off. You can also access flags as a keyvalue, spawnflags. That's what the flags actually are; a specific number determined by the combination of flags that are checked.

Warning:spawnflags is an signed int in-game, but an unsigned long in Hammer!