Add SP changes to HL2MP gravity gun + clientside +USE prediction

Author: Blixibon

src/game/client/c_baseentity.h

@@ -1047,6 +1047,11 @@ class C_BaseEntity : public IClientEntity
 	// are relative to the attachment on this entity.
 	void SetParent( C_BaseEntity *pParentEntity, int iParentAttachment=0 );
 
+#ifdef MAPBASE_MP
+	// Some entities should predict +USE interaction
+	virtual void			Use( CBaseEntity *pActivator, CBaseEntity *pCaller, USE_TYPE useType, float value ) {}
+#endif
+
 	bool					PhysicsRunThink( thinkmethods_t thinkMethod = THINK_FIRE_ALL_FUNCTIONS );
 	bool					PhysicsRunSpecificThink( int nContextIndex, BASEPTR thinkFunc );
 

src/game/client/c_baseplayer.cpp

@@ -2448,6 +2448,13 @@ void C_BasePlayer::PostThink( void )
 		{
 			SetCollisionBounds( VEC_HULL_MIN, VEC_HULL_MAX );
 		}
+
+#ifdef MAPBASE_MP
+		if ( m_hUseEntity != NULL )
+		{
+			m_hUseEntity->Use( this, this, USE_SET, 2 );
+		}
+#endif
 
 		if ( !CommentaryModeShouldSwallowInput( this ) )
 		{

src/game/server/hl2/func_tank.cpp

@@ -1111,6 +1111,23 @@ void CFuncTank::UpdateOnRemove( void )
 	BaseClass::UpdateOnRemove();
 }
 
+#ifdef MAPBASE_MP
+void CFuncTank::AddEffects( int nEffects )
+{ 
+	if ( nEffects & EF_NODRAW && gpGlobals->maxClients > 1 )
+	{
+		// The client needs to know that we are the +USE entity for prediction, but EF_NODRAW prevents that.
+		// Swallow nodraw and turn invisible in a way that transmits to the client.
+		nEffects &= ~(EF_NODRAW);
+
+		nEffects |= EF_NOSHADOW;
+		SetRenderMode( kRenderNone );
+	}
+
+	BaseClass::AddEffects( nEffects );
+}
+#endif
+
 
 //-----------------------------------------------------------------------------
 // Barrel position

src/game/server/hl2/func_tank.h

@@ -91,6 +91,10 @@ class CFuncTank : public CBaseEntity
 	bool	KeyValue( const char *szKeyName, const char *szValue );
 	void	UpdateOnRemove();
 
+#ifdef MAPBASE_MP
+	void	AddEffects( int nEffects );
+#endif
+
 	void	SetYawRate( float flYawRate ) { m_yawRate = flYawRate; }
 	void	SetPitchRate( float flPitchRate ) { m_pitchRate = flPitchRate; }