Core/Unit: Fix movement hiccups in water (#24020)

* Core/Unit: Allow to define Units which can enter water but cannot swim

Allow to define Units which can enter water but cannot swim, i.e. crabs walking at the bottom of a sea.

* Add UNIT_FLAG_SWIMMING to creatures when entering combat

* Fix charmed creatures not entering water

* Always allow Creatures controlled by players to enter water

* Add swimming flag when possessing a unit and remove it properly at the end, even if the creature engaged combat before and after.
When adding/removing UNIT_FLAG_SWIMMING manually calling Creature::RefreshSwimmingFlag(true) might be required.

(cherry picked from commit fc1a0d936888395f114028af3337e7d674e0a43c)

src/server/game/Entities/Creature/Creature.cpp

@@ -305,7 +305,7 @@ Creature::Creature(bool isWorldObject): Unit(isWorldObject), MapObject(), m_grou
     m_defaultMovementType(IDLE_MOTION_TYPE), m_spawnId(UI64LIT(0)), m_equipmentId(0), m_originalEquipmentId(0), m_AlreadyCallAssistance(false), m_AlreadySearchedAssistance(false), m_cannotReachTarget(false), m_cannotReachTimer(0),
     m_meleeDamageSchoolMask(SPELL_SCHOOL_MASK_NORMAL), m_originalEntry(0), m_homePosition(), m_transportHomePosition(), m_creatureInfo(nullptr), m_creatureData(nullptr), _waypointPathId(0), _currentWaypointNodeInfo(0, 0),
     m_formation(nullptr), m_triggerJustAppeared(true), m_respawnCompatibilityMode(false), _lastDamagedTime(0),
-    _regenerateHealth(true), _regenerateHealthLock(false)
+    _regenerateHealth(true), _regenerateHealthLock(false), _isMissingSwimmingFlagOutOfCombat(false)
 {
     m_regenTimer = CREATURE_REGEN_INTERVAL;
 
@@ -2829,7 +2829,7 @@ void Creature::UpdateMovementFlags()
     if (!isInAir)
         RemoveUnitMovementFlag(MOVEMENTFLAG_FALLING);
 
-    SetSwim(GetMovementTemplate().IsSwimAllowed() && IsInWater());
+    SetSwim(CanSwim() && IsInWater());
 }
 
 CreatureMovementData const& Creature::GetMovementTemplate() const
@@ -2840,6 +2840,36 @@ CreatureMovementData const& Creature::GetMovementTemplate() const
     return GetCreatureTemplate()->Movement;
 }
 
+bool Creature::CanSwim() const
+{
+    if (Unit::CanSwim())
+        return true;
+
+    if (IsPet())
+        return true;
+
+    return false;
+}
+
+bool Creature::CanEnterWater() const
+{
+    if (CanSwim())
+        return true;
+
+    return GetMovementTemplate().IsSwimAllowed();
+}
+
+void Creature::RefreshSwimmingFlag(bool recheck)
+{
+    if (!_isMissingSwimmingFlagOutOfCombat || recheck)
+        _isMissingSwimmingFlagOutOfCombat = !HasUnitFlag(UNIT_FLAG_CAN_SWIM);
+
+    // Check if the creature has UNIT_FLAG_SWIMMING and add it if it's missing
+    // Creatures must be able to chase a target in water if they can enter water
+    if (_isMissingSwimmingFlagOutOfCombat && CanEnterWater())
+        AddUnitFlag(UNIT_FLAG_CAN_SWIM);
+}
+
 void Creature::AllLootRemovedFromCorpse()
 {
     if (loot.loot_type != LOOT_SKINNING && !IsPet() && GetCreatureTemplate()->SkinLootId && hasLootRecipient())
@@ -3418,6 +3448,8 @@ void Creature::AtEngage(Unit* target)
     if (!(GetCreatureTemplate()->type_flags & CREATURE_TYPE_FLAG_MOUNTED_COMBAT_ALLOWED))
         Dismount();
 
+    RefreshSwimmingFlag();
+
     if (IsPet() || IsGuardian()) // update pets' speed for catchup OOC speed
     {
         UpdateSpeed(MOVE_RUN);

src/server/game/Entities/Creature/Creature.h

@@ -111,7 +111,8 @@ class TC_GAME_API Creature : public Unit, public GridObject<Creature>, public Ma
 
         CreatureMovementData const& GetMovementTemplate() const;
         bool CanWalk() const { return GetMovementTemplate().IsGroundAllowed(); }
-        bool CanSwim() const override { return GetMovementTemplate().IsSwimAllowed() || IsPet(); }
+        bool CanSwim() const override;
+        bool CanEnterWater() const override;
         bool CanFly()  const override { return GetMovementTemplate().IsFlightAllowed() || IsFlying(); }
         bool CanHover() const { return GetMovementTemplate().Ground == CreatureGroundMovementType::Hover || IsHovering(); }
 
@@ -369,6 +370,12 @@ class TC_GAME_API Creature : public Unit, public GridObject<Creature>, public Ma
         void AtEngage(Unit* target) override;
         void AtDisengage() override;
 
+        bool HasSwimmingFlagOutOfCombat() const
+        {
+            return !_isMissingSwimmingFlagOutOfCombat;
+        }
+        void RefreshSwimmingFlag(bool recheck = false);
+
         std::string GetDebugInfo() const override;
 
     protected:
@@ -452,6 +459,8 @@ class TC_GAME_API Creature : public Unit, public GridObject<Creature>, public Ma
         // Regenerate health
         bool _regenerateHealth; // Set on creation
         bool _regenerateHealthLock; // Dynamically set
+
+        bool _isMissingSwimmingFlagOutOfCombat;
 };
 
 class TC_GAME_API AssistDelayEvent : public BasicEvent

src/server/game/Entities/Player/Player.h

@@ -2623,6 +2623,7 @@ class TC_GAME_API Player : public Unit, public GridObject<Player>
         void SendMovementSetCollisionHeight(float height, WorldPackets::Movement::UpdateCollisionHeightReason reason);
 
         bool CanFly() const override { return m_movementInfo.HasMovementFlag(MOVEMENTFLAG_CAN_FLY); }
+        bool CanEnterWater() const override { return true; }
 
         std::string GetMapAreaAndZoneString() const;
         std::string GetCoordsMapAreaAndZoneString() const;

src/server/game/Entities/Unit/Unit.cpp

@@ -3006,7 +3006,7 @@ bool Unit::isInBackInMap(Unit const* target, float distance, float arc) const
 bool Unit::isInAccessiblePlaceFor(Creature const* c) const
 {
     if (IsInWater())
-        return c->CanSwim();
+        return c->CanEnterWater();
     else
         return c->CanWalk() || c->CanFly();
 }
@@ -11150,6 +11150,9 @@ bool Unit::SetCharmedBy(Unit* charmer, CharmType type, AuraApplication const* au
 
     AddUnitState(UNIT_STATE_CHARMED);
 
+    if (Creature* creature = ToCreature())
+        creature->RefreshSwimmingFlag();
+
     if ((GetTypeId() != TYPEID_PLAYER) || (charmer->GetTypeId() != TYPEID_PLAYER))
     {
         // AI will schedule its own change if appropriate
@@ -12107,7 +12110,7 @@ bool Unit::CanSwim() const
         return true;
     if (HasUnitFlag2(UnitFlags2(0x1000000)))
         return false;
-    if (IsPet() && HasUnitFlag(UNIT_FLAG_PET_IN_COMBAT))
+    if (HasUnitFlag(UNIT_FLAG_PET_IN_COMBAT))
         return true;
     return HasUnitFlag(UnitFlags(UNIT_FLAG_RENAME | UNIT_FLAG_CAN_SWIM));
 }

src/server/game/Entities/Unit/Unit.h

@@ -1807,6 +1807,7 @@ class TC_GAME_API Unit : public WorldObject
         virtual bool CanFly() const = 0;
         bool IsFlying() const   { return m_movementInfo.HasMovementFlag(MOVEMENTFLAG_FLYING | MOVEMENTFLAG_DISABLE_GRAVITY); }
         bool IsFalling() const;
+        virtual bool CanEnterWater() const = 0;
         virtual bool CanSwim() const;
 
         float GetHoverOffset() const

src/server/game/Movement/MovementGenerators/HomeMovementGenerator.cpp

@@ -144,6 +144,9 @@ void HomeMovementGenerator<Creature>::DoFinalize(Creature* owner, bool active, b
 
     if (movementInform && HasFlag(MOVEMENTGENERATOR_FLAG_INFORM_ENABLED))
     {
+        if (!owner->HasSwimmingFlagOutOfCombat())
+            owner->RemoveUnitFlag(UNIT_FLAG_CAN_SWIM);
+
         owner->SetSpawnHealth();
         owner->LoadCreaturesAddon();
         if (owner->IsVehicle())

src/server/game/Movement/PathGenerator.cpp

@@ -657,7 +657,7 @@ void PathGenerator::CreateFilter()
             includeFlags |= NAV_GROUND;          // walk
 
         // creatures don't take environmental damage
-        if (creature->CanSwim())
+        if (creature->CanEnterWater())
             includeFlags |= (NAV_WATER | NAV_MAGMA_SLIME);                 // swim
     }
     else // assume Player