Tutorial: Coding Fog Last edited 17 years ago2007-02-28 05:00:00 UTC

Add Fog to your Mod

by darkphoenix_68

(The mod originally posted by Highlander formed the basis of my work, but as originally posted it contained several errors that prevented it from working. The TWHL Admins kindly agreed to allow me to revise his tutorial. Needless to say, without his original tutorial as a starting point, I would never have gotten this code to work as it now does. Additional credit (as originally extended by Highlander) goes to Confused, Sysop, and Cause of Death.)

• Requires Half-Life SDK 2.3, a little coding experience, and your favourite Mod compiler!
• Assumes you know how to compile DLL files and create/revise a Mod.

If you want to add fog to one or more maps in your Half-Life mod, this tutorial will show you how to do it.

Fog

This fog is a visual effect, controlled by a point entity (an env_fog) which you can insert into your level. It can be toggled on or off as required. It can be any colour you choose, and its apparent density is controlled by setting the start and end distances over which the effect is applied.

Sadly, the code also has its limitations:

• It only works under the OpenGL video driver; neither Software nor Direct3D are currently supported. (I did look briefly into adding Direct3D support, but since I don't actually use it -- and since it never worked under the initial implementation either -- I decided to leave it as an exercise for the reader! )
• Being point-based rather than brush-based, you would need some careful level design if you wanted both foggy and fog-free areas. Its switchability helps here -- for single-player levels, anyway! (I suspect brush-based fog could be developed by looking into the water-handling code; that's another exercise for another time!)
• The way the code handles sky leaves a little to be desired, with the skybox occasionally flickering into partial view through the fog as you turn. Again, careful level design could resolve this issue! Other than this flicker, the sky will be fully masked by your fog colour!

So, if you want to go ahead and add support for this client-based point-entity fog to your mod, read on.

General Comments

The following tutorial is quite code-intensive, and unfortunately the bbCode used here on TWHL does not preserve indentation, so it may look a little messy. However, it does work (I've tested it extensively) and it will work whether it is indented or not. Obviously, for your own sanity, you may wish to reindent as appropriate! The other artifact of the site itself of which you should be aware is that some lines of code wrap when they reach the edge of the page; it should be obvious, but watch out for it anyway!

I have scattered additional

[green]// explanatory comments[/green]

throughout the code. These form part of the tutorial, but are (obviously) not necessary to the compiler; however, I hope they will assist in explaining what is going on. (Or, I guess, make it quite clear that I do not know what is going on...)

Existing code (shown for reference and/or context) is in

[font=blue][i]blue italics[/i][/font]

. In many cases I have given approximate line numbers; these are only approximate, because my files contain other code changes not relevant to this tutorial... If the line number does not help you locate the piece of code I am changing, your Find... tool is your friend!

Files to be edited are shown in

[red][b]red[/b][/red]

.

Server-side: The ClientFog Class

First we need to create support for the env_fog entity. This is done server-side (in the

dlls

directory, and the associated Project/Workspace.)

Open the

[red][b]dlls/effects.cpp[/b][/red]

file in your favourite editor and add the following code at the end of the file:

//=======================
// ClientFog
//=======================
extern int gmsgSetFog;

[green]// This is the flag defined by the env_fog entity[/green]
[/pre][pre]#define SF_FOG_STARTOFF		0x0001
LINK_ENTITY_TO_CLASS( env_fog, CClientFog );
[/pre][pre]
[green]/*
// While a CClientFog constructor is not actually necessary for
// this code, you might find use for one down the track,
// in which case it may look like this:
CClientFog *CClientFog::FogCreate( void )
{
	CClientFog *pFog = GetClassPtr( (CClientFog *)NULL );
	pFog->pev->classname = MAKE_STRING("env_fog");
	pFog->Spawn();
	return pFog;
}
/*[/green]
[/pre][pre]
[green]// Spawns our env_fog entity and sets the m_active flag.[/green]
void CClientFog :: Spawn ( void )
{
	pev->solid			= SOLID_NOT;
	pev->movetype		= MOVETYPE_NONE;
    pev->effects		= 0;
	if ( pev->spawnflags & SF_FOG_STARTOFF )
		m_active = 0;
	else
	{
		SetThink( FogThink );
		pev->nextthink = gpGlobals->time + 0.01;
		m_active = 1;
	}
}
[/pre][pre]
[green]// Reads salient values from the env_fog entity[/green]
void CClientFog :: KeyValue( KeyValueData *pkvd )
{
    if (FStrEq(pkvd->szKeyName, "startdist"))
    {
        m_iStartDist = atoi(pkvd->szValue);
        pkvd->fHandled = TRUE;
    }
    else if (FStrEq(pkvd->szKeyName, "enddist"))
    {
        m_iEndDist = atoi(pkvd->szValue);
        pkvd->fHandled = TRUE;
    }
    else
        CBaseEntity::KeyValue( pkvd );
}
[/pre][pre]
[green]// Essentially turns our fog effect on/off by sending a message to the client.
// Anything which changes m_active should force a FogThink.[/green]
void CClientFog :: FogThink ( void )
{
	if ( m_active )
	{
        MESSAGE_BEGIN( MSG_ALL, gmsgSetFog, NULL );
        WRITE_SHORT ( pev->rendercolor.x );
        WRITE_SHORT ( pev->rendercolor.y );
        WRITE_SHORT ( pev->rendercolor.z );
        WRITE_SHORT ( m_iStartDist );
        WRITE_SHORT ( m_iEndDist );
        MESSAGE_END();
    }
	else
	{
        MESSAGE_BEGIN( MSG_ALL, gmsgSetFog, NULL );
        WRITE_SHORT ( 0 );
        WRITE_SHORT ( 0 );
        WRITE_SHORT ( 0 );
        WRITE_SHORT ( 0 );
        WRITE_SHORT ( 0 );
        MESSAGE_END();
	}
}
[/pre][pre]
[green]// Called when the entity is triggered.[/green]
void CClientFog::Use( CBaseEntity *pActivator, CBaseEntity *pCaller, USE_TYPE useType, float value )
{
	if ( ShouldToggle( useType, m_active ) )
		m_active = !m_active;
	SetThink( FogThink );
	pev->nextthink = gpGlobals->time + 0.01;
}
[/pre][pre]
[green]// These macros set up the save/restore code for the CClientFog object[/green]
TYPEDESCRIPTION CClientFog::m_SaveData[] =
{
    DEFINE_FIELD( CClientFog, m_active, FIELD_BOOLEAN ),
    DEFINE_FIELD( CClientFog, m_iStartDist, FIELD_INTEGER ),
    DEFINE_FIELD( CClientFog, m_iEndDist,FIELD_INTEGER ),
};

IMPLEMENT_SAVERESTORE(CClientFog,CBaseEntity);

The declarations for the above code need to be added to

effects.h

(you'll note some of the classes defined in

effects.cpp

have their declarations in the .cpp file, but we need to make our fog visible to other files!) Place the following code at the bottom of the

[red][b]dlls/effects.h[/b][/red]

file, just above the final

[font=blue][i]#endif[/i][/font]

line:

//=======================
// ClientFog
//=======================
class CClientFog : public CBaseEntity
{
    public:
[green]/*
// As stated above, this constructor is not needed; add if required!
        static CClientFog *FogCreate( void );
*/[/green]
        void Spawn( void );
        void KeyValue( KeyValueData *pkvd );
        void EXPORT FogThink( void );
        void Use( CBaseEntity *pActivator, CBaseEntity *pCaller, USE_TYPE useType, float value );
        int m_iStartDist;
        int m_iEndDist;
        bool m_active;
        virtual int Save( CSave &save );
        virtual int Restore( CRestore &restore );
        static TYPEDESCRIPTION m_SaveData[];
};

This gives us the code we need to initialise our fog to the values set in the env_fog entity. However there are still a couple of minor problems to tackle...

Server-side: Fog Status Messages

Whenever a new player joins the server, it needs to send a fog status message to the client. There are three possible situations in which the client needs to be updated, and we need to cover them all:

• A new level is loaded;
• A new player joins a running multi-player server;
• A player respawns after dying.

Our first problem is that we cannot directly detect a change of map. Let's change that by hooking into code which is called at every level change.

First we shall add our variable declaration to the bottom of

[red][b]dlls/globals.cpp[/b][/red]

:

DLL_GLOBAL int          gLevelLoaded;

Now we set it at the appropriate moment; let's edit

[red][b]dlls/world.cpp[/b][/red]

:

Somewhere around line #43, you will find:

[font=blue][i]extern DLL_GLOBAL	int			gDisplayTitle;[/i][/font]

Add the following line below that:

extern DLL_GLOBAL	int			gLevelLoaded;

Now, down around line #479 you should find the

[font=blue][i]CWorld :: Precache[/i][/font]

function, to which you need to add the following line:

[val][i]void CWorld :: Precache( void )
{
	g_pLastSpawn = NULL;[/i][/val]
	gLevelLoaded = TRUE;	[green]// Handles "level loaded" case[/green]

With that out of the way, let's handle the player spawning cases. First we'll declare our variable in

[red][b]dlls/player.h[/b][/red]

(somewhere around line #90):

[val][i]class CBasePlayer : public CBaseMonster
{
public:[/i][/val]
    BOOL                m_bRespawned; [green]// True when fog update msg needs to be sent[/green]

Now we can modify our player code to pull all of this together. Be brave; there are many small changes scattered through this next file. Open

[red][b]dlls/player.cpp[/b][/red]

-- and here we go!

First we need to find the following line (at around line #45):

[font=blue][i]extern DLL_GLOBAL int		g_iSkillLevel, gDisplayTitle;[/i][/font]

and change it to look like this:

extern DLL_GLOBAL int		g_iSkillLevel, gDisplayTitle, gLevelLoaded;

A little further down you will find a whole list of

[font=blue][i]int[/i][/font]

initialisation lines; look for:

[font=blue][i]int gmsgTeamNames = 0;[/i][/font]

and add the following on the next line:

int gmsgSetFog = 0;

Just below that you will find

[font=blue][i]LinkUserMessages[/i][/font]

function; add

gmsgSetFog

somewhere near the top, like so:

[val][i]void LinkUserMessages( void )
{
	// Already taken care of?
	if ( gmsgSelAmmo )
	{
		return;
	}[/i][/val]
	[green]// This basically registers "SetFog" as a known message to be sent to the server[/green]
	gmsgSetFog = REG_USER_MSG("SetFog", -1 );
[font=blue][i]	gmsgSelAmmo = REG_USER_MSG("SelAmmo", sizeof(SelAmmo));[/i][/font]

Now you want to jump down to the

[font=blue][i]CBasePlayer::PlayerDeathThink[/i][/font]

function; this will be somewhere around line #1150 to #1200. Right at the bottom of the function, just before the

[font=blue][i]respawn[/i][/font]

call, you want to add the following:

[font=blue][i]	//ALERT(at_console, "Respawn
");[/i][/font]
    m_bRespawned = TRUE;	[green]// Handles "player respawned" case[/green]
[font=blue][i]	respawn(pev, !(m_afPhysicsFlags & PFLAG_OBSERVER) );// don't copy a corpse if we're in deathcam.[/i][/font]

Down around line #2700 to #2800 is

[font=blue][i]CBasePlayer::Spawn[/i][/font]

; add the following line right near the bottom of the function:

[font=blue][i]	m_flNextChatTime = gpGlobals->time;[/i][/font]
	m_bRespawned = TRUE;	[green]// Handles "new player" case[/green]
[font=blue][i]	g_pGameRules->PlayerSpawn( this );[/i][/font]

We're almost done. Now that we have detected all of the cases for which we need to send our fog status message, all we need to do is actually process that information. The best place to do that is in the

[font=blue][i]CBasePlayer::UpdateClientData[/i][/font]

function, down around line #3800. You can probably insert the following snippet of code at any convenient point in this function; I slotted mine between the

[font=blue][i]if ( m_iFOV != m_iClientFOV )[/i][/font]

and the

[font=blue][i]if (gDisplayTitle)[/i][/font]

:

[val][i]
	if ( m_iFOV != m_iClientFOV )
	{
	:
	:
	}
[/i][/val]
    if ( m_bRespawned || gLevelLoaded )
    {
        CBaseEntity *pEntity = NULL;
        pEntity = UTIL_FindEntityByClassname( pEntity, "env_fog" );
        if ( pEntity )
        {
            CClientFog *pFog = (CClientFog *)pEntity;
			[green]// CClientFog::FogThink handles the actual message sending, so let's force a think[/green]
			pFog->pev->nextthink = gpGlobals->time + 0.01;
        }
		m_bRespawned = gLevelLoaded = FALSE;
    }
[val][i]
	// HACKHACK -- send the message to display the game title
	if (gDisplayTitle)
	{
	:
	:
	}
[/i][/val]

That's it for the server-side code. Before we leave the

dlls

directory, we can probably compile the server dll -- or leave it till we're fully finished; whatever works best for you!

Client-side: Incoming Messages

At this point, the server has initialised the fog, detected everything it needs to detect, and sent a fog status message hurtling through the void (sorry, bad pun!) towards the client(s). Now we just need to convince the client to catch them! To do that, we'll leave the safety of

dlls

and move over to the

cl_dlls

directory (and associated Project/Workspace!)

First we'll ask the HUD to catch the incoming message. Open

[red][b]cl_dlls/hud.cpp[/b][/red]

and look for

[font=blue][i]__MsgFunc_GameMode[/i][/font]

at around line #130. Add the following:

[val][i]int __MsgFunc_GameMode(const char *pszName, int iSize, void *pbuf )
{
	return gHUD.MsgFunc_GameMode( pszName, iSize, pbuf );
}
[/i][/val]
int __MsgFunc_SetFog(const char *pszName, int iSize, void *pbuf )
{
    return gHUD.MsgFunc_SetFog( pszName, iSize, pbuf );
}

Further down, around line #300, you will find a whole list of

[font=blue][i]HOOK_MESSAGE[/i][/font]

macros in no particular order. Add:

HOOK_MESSAGE( SetFog );

to the list. (I added it between

[font=blue][i]HOOK_MESSAGE(TeamInfo);[/i][/font]

and

[font=blue][i]HOOK_MESSAGE(Spectator);[/i][/font]

, but I don't suppose its placement is critical. It might almost be nice if the list was sorted alphabetically, but that's up to you -- and more to the point, it may break everything, so let's leave that for another time! )

To follow through on our changes to the

.cpp

file, open the

[red][b]cl_dlls/hud.h[/b][/red]

file; look for

[font=blue][i]	int  _cdecl MsgFunc_Concuss( const char *pszName, int iSize, void *pbuf );[/i][/font]

somewhere near line #640, and after it add:

int  _cdecl MsgFunc_SetFog(const char *pszName, int iSize, void *pbuf );

Now that we've caught the message from the server, let's process it. To do this we need

[red][b]cl_dlls/hud_msg.cpp[/b][/red]

. Before we do anything else, let's declare the variables we're going to use. After the initial

[font=blue][i]#include[/i][/font]

s and

[font=blue][i]#define[/i][/font]

s, add the following:

float g_fFogColor[3];
float g_fStartDist;
float g_fEndDist;

A couple of lines down from there, we shall reset our fog distance values when we reset the HUD:

[val][i]int CHud :: MsgFunc_ResetHUD(const char *pszName, int iSize, void *pbuf )
{
	ASSERT( iSize == 0 );[/val][/i]
	g_fStartDist = 0.0;
g_fEndDist = 0.0;

Right at the bottom of the file, we'll add our

SetFog

function which actually interprets the received message:

int CHud :: MsgFunc_SetFog( const char *pszName, int iSize, void *pbuf )
{
    BEGIN_READ( pbuf, iSize );
    g_fFogColor[0] = (float)READ_SHORT(); // R
    g_fFogColor[1] = (float)READ_SHORT(); // G
    g_fFogColor[2] = (float)READ_SHORT(); // B
    g_fStartDist = (float)READ_SHORT();
    g_fEndDist = (float)READ_SHORT();
    return 1;
}

Where The Magic Happens

We're on the home straight now. We've done everything except actually display the fog. (Well, almost everything, but I'll get to that!) The file we want to edit now is

tri.cpp

. This is the file which confused me the most when I was originally trying the get the code to work -- but it was only once I started looking further afield that I solved the puzzle. Anyway, without further ado, let's open

[red][b]cl_dlls/tri.cpp[/b][/red]

. Just after the initial

[font=blue][i]#include[/i][/font]

s and

[font=blue][i]#define[/i][/font]

s, we'll access the variables we set up previously:

extern float g_fFogColor[3];
extern float g_fStartDist;
extern float g_fEndDist;

After the

[font=blue][i]extern "C" { ... }[/i][/font]

declarations, we'll add the heart of the whole thing:

void RenderFog ( void )
{
	static float fColorBlack[3] = {0,0,0};
	if (g_fStartDist > 0.0 && g_fEndDist > 0.0)
		gEngfuncs.pTriAPI->Fog ( g_fFogColor, g_fStartDist, g_fEndDist, 1 );
	else
		gEngfuncs.pTriAPI->Fog ( fColorBlack, g_fStartDist, g_fEndDist, 0 );
}

And now for the thing that really confused me. At the bottom of the file we have

[font=blue][i]HUD_DrawNormalTriangles[/i][/font]

and

[font=blue][i]HUD_DrawTransparentTriangles[/i][/font]

. Extensive testing led me to the inescapable conclusion that each apparently does the other's job:

[font=blue][i]HUD_DrawNormalTriangles[/i][/font]

handles "transparent" faces and

[font=blue][i]HUD_DrawTransparentTriangles[/i][/font]

handles -- well, everything. Of course, all you really need to know is to change the latter function as follows:

[i][val]/*
=================
HUD_DrawTransparentTriangles
[/val]
[green]Despite the name, it appears that this actually controls
non-transparent entities and world brushes[/green][val]
=================
*/
void DLLEXPORT HUD_DrawTransparentTriangles( void )
{[/val][/i]
    RenderFog();
[val][i]#if defined( TEST_IT )
//	Draw_Triangles();
#endif
}[/i][/val]

That's it! Compile that, and if all goes according to plan you'll have working fog.

(Well, there's still that "almost" to take care of. I'll get there in a second. Just as an aside, though, while we're here: see that

[font=blue][i]#if defined( TEST_IT ) ... #endif[/i][/font]

? While playing with this file I compiled in the

[font=blue][i]Draw_Triangles()[/i][/font]

code. The whole thing (ie, Half-Life) fell over while trying to start a map, so I hastily got rid of it again. As soon as I'm done with this tutorial I shall probably clean all that code out to make the file a little neater...)

The Final Step

So what remains to be done? Adding the env_fog entity to your map, of course. If you use Valve Hammer Editor, you can add the following to whichever FGD file you are mapping with:

@PointClass base(Targetname) size(-16 -16 -16, 16 16 16) = env_fog : "Client Fog"
[
    startdist(integer) : "Start Distance" : 1
    enddist(integer) : "End Distance" : 1500
    rendercolor(color255) : "Fog Color (R G B)" : "0 0 0"
	spawnflags(Flags) =
	[
		1 : "Start Off" 	: 0
	]
]

Since VHE does no sorting of its own, it probably makes sense to add this between env_explosion and env_global -- ie, alphabetically! You will now be able to add env_fogs to your maps -- although be warned, I'm not sure what will happen if you have more than one per level. I'd imagine if you had several with different colours, you could trigger them off and on to change the colour of your fog -- but I have not tested that!

Unfortunately I am not familiar with any other editors used to make HL maps. No doubt they have a way of adding new entities, similar to the FGD file in Hammer -- but you'll need to figure that out for yourself! Sorry...

Wrap Up

What I have done is produce a small (and exceedingly ugly) test map for you to check out. I guess you could play with that to add multiple env_fog entities, or whatever else you wanted to try. In the map you will find several transparent objects ("texture"-rendered and "solid"-rendered) because that was what I was having the most difficulty with initially. You will also find a large target which, if shot, will toggle the fog on and off.

It is quite a bit of coding to get to this point, but I hope my directions have been clear enough that we all arrived here with code which compiles and, y'know, actually works! If you have any problems let me know and I'll see if I can help out.

Have fun!

if ( gInitHUD )
{
    m_fInitHUD = TRUE;
    m_bSendMessages = TRUE;
}