Fix monster_tentacle not interpolating

ValveSoftware/halflife#3228

dlls/cbase.cpp

@@ -617,6 +617,7 @@ CBaseEntity* CBaseEntity::GetNextTarget()
 TYPEDESCRIPTION CBaseEntity::m_SaveData[] =
 	{
 		DEFINE_FIELD(CBaseEntity, m_pGoalEnt, FIELD_CLASSPTR),
+		DEFINE_FIELD(CBaseEntity, m_EFlags, FIELD_CHARACTER),
 
 		DEFINE_FIELD(CBaseEntity, m_pfnThink, FIELD_FUNCTION), // UNDONE: Build table of these!!!
 		DEFINE_FIELD(CBaseEntity, m_pfnTouch, FIELD_FUNCTION),

dlls/cbase.h

@@ -152,6 +152,11 @@ class CBaseEntity
 	CBaseEntity* m_pGoalEnt; // path corner we are heading towards
 	CBaseEntity* m_pLink;	 // used for temporary link-list operations.
 
+	/**
+	*	@brief Entity flags sent to the client in ::AddToFullPack
+	*/
+	byte m_EFlags = 0;
+
 	virtual ~CBaseEntity() {}
 
 	// initialization functions

dlls/client.cpp

@@ -1086,6 +1086,8 @@ int AddToFullPack(struct entity_state_s* state, int e, edict_t* ent, edict_t* ho
 {
 	int i;
 
+	auto entity = reinterpret_cast<CBaseEntity*>(GET_PRIVATE(ent));
+
 	// don't send if flagged for NODRAW and it's not the host getting the message
 	if ((ent->v.effects & EF_NODRAW) != 0 &&
 		(ent != host))
@@ -1201,6 +1203,8 @@ int AddToFullPack(struct entity_state_s* state, int e, edict_t* ent, edict_t* ho
 		state->eflags &= ~EFLAG_SLERP;
 	}
 
+	state->eflags |= entity->m_EFlags;
+
 	state->scale = ent->v.scale;
 	state->solid = ent->v.solid;
 	state->colormap = ent->v.colormap;

dlls/tentacle.cpp

@@ -257,6 +257,9 @@ void CTentacle::Spawn()
 	pev->health = 75;
 	pev->sequence = 0;
 
+	//Always interpolate tentacles since they don't actually move.
+	m_EFlags |= EFLAG_SLERP;
+
 	SET_MODEL(ENT(pev), "models/tentacle2.mdl");
 	UTIL_SetSize(pev, Vector(-32, -32, 0), Vector(32, 32, 64));