Core/Movement: Replace old TargetedMovementGenerator into ChaseMovementGenerator and FollowMovementGenerator, full rewrite for both.

- Chase to angle is now functional. Pets use this to chase behind the target. Closes #19925.
- Chase to arbitrary range interval works. Not used anywhere, but you can technically make hunter-like mobs.
- Pets now follow the hunter cleanly and without stutter stepping. Also fix some other things. Closes #8924.

2 files changed, 40 insertions, 32 deletions

diff --git a/src/server/game/Entities/Unit/Unit.cpp b/src/server/game/Entities/Unit/Unit.cpp
index 0b31a125cd8..b5d04826d85 100644
--- a/src/server/game/Entities/Unit/Unit.cpp
+++ b/src/server/game/Entities/Unit/Unit.cpp
@@ -17,6 +17,7 @@
  */
 
 #include "Unit.h"
+#include "AbstractFollower.h"
 #include "Battlefield.h"
 #include "BattlefieldMgr.h"
 #include "Battleground.h"
@@ -538,14 +539,14 @@ bool Unit::IsWithinCombatRange(Unit const* obj, float dist2compare) const
     return distsq < maxdist * maxdist;
 }
 
-bool Unit::IsWithinMeleeRange(Unit const* obj) const
+bool Unit::IsWithinMeleeRangeAt(Position const& pos, Unit const* obj) const
 {
     if (!obj || !IsInMap(obj) || !InSamePhase(obj))
         return false;
 
-    float dx = GetPositionX() - obj->GetPositionX();
-    float dy = GetPositionY() - obj->GetPositionY();
-    float dz = GetPositionZ() - obj->GetPositionZ();
+    float dx = pos.GetPositionX() - obj->GetPositionX();
+    float dy = pos.GetPositionY() - obj->GetPositionY();
+    float dz = pos.GetPositionZ() - obj->GetPositionZ();
     float distsq = dx*dx + dy*dy + dz*dz;
 
     float maxdist = GetMeleeRange(obj);
@@ -8509,25 +8510,7 @@ void Unit::UpdateSpeed(UnitMoveType mtype)
         {
             // Set creature speed rate
             if (GetTypeId() == TYPEID_UNIT)
-            {
-                Unit* pOwner = GetCharmerOrOwner();
-                if ((IsPet() || IsGuardian()) && !IsInCombat() && pOwner) // Must check for owner or crash on "Tame Beast"
-                {
-                    // For every yard over 5, increase speed by 0.01
-                    //  to help prevent pet from lagging behind and despawning
-                    float dist = GetDistance(pOwner);
-                    float base_rate = 1.00f; // base speed is 100% of owner speed
-
-                    if (dist < 5)
-                        dist = 5;
-
-                    float mult = base_rate + ((dist - 5) * 0.01f);
-
-                    speed *= pOwner->GetSpeedRate(mtype) * mult; // pets derive speed from owner when not in combat
-                }
-                else
-                    speed *= ToCreature()->GetCreatureTemplate()->speed_run;    // at this point, MOVE_WALK is never reached
-            }
+                speed *= ToCreature()->GetCreatureTemplate()->speed_run;    // at this point, MOVE_WALK is never reached
 
             // Normalize speed by 191 aura SPELL_AURA_USE_NORMAL_MOVEMENT_SPEED if need
             /// @todo possible affect only on MOVE_RUN
@@ -8551,11 +8534,27 @@ void Unit::UpdateSpeed(UnitMoveType mtype)
             break;
     }
 
-    // for creature case, we check explicit if mob searched for assistance
-    if (GetTypeId() == TYPEID_UNIT)
+    if (Creature* creature = ToCreature())
     {
-        if (ToCreature()->HasSearchedAssistance())
+        // for creature case, we check explicit if mob searched for assistance
+        if (creature->HasSearchedAssistance())
             speed *= 0.66f;                                 // best guessed value, so this will be 33% reduction. Based off initial speed, mob can then "run", "walk fast" or "walk".
+
+        if (creature->HasUnitTypeMask(UNIT_MASK_MINION) && !creature->IsInCombat())
+        {
+            MovementGenerator* top = creature->GetMotionMaster()->top();
+            if (top && top->GetMovementGeneratorType() == FOLLOW_MOTION_TYPE)
+            {
+                Unit* followed = ASSERT_NOTNULL(dynamic_cast<AbstractFollower*>(top))->GetTarget();
+                if (followed && followed->GetGUID() == GetOwnerGUID() && !followed->IsInCombat())
+                {
+                    float ownerSpeed = followed->GetSpeedRate(mtype);
+                    if (speed < ownerSpeed || creature->IsWithinDist3d(followed, 10.0f))
+                        speed = ownerSpeed;
+                    speed *= std::min(std::max(1.0f, 0.75f + (GetDistance(followed) - PET_FOLLOW_DIST) * 0.05f), 1.3f);
+                }
+            }
+        }
     }
 
     // Apply strongest slow aura mod to speed
@@ -8656,6 +8655,12 @@ void Unit::SetSpeedRate(UnitMoveType mtype, float rate)
     }
 }
 
+void Unit::RemoveAllFollowers()
+{
+    while (!m_followingMe.empty())
+        (*m_followingMe.begin())->SetTarget(nullptr);
+}
+
 bool Unit::IsGhouled() const
 {
     return HasAura(SPELL_DK_RAISE_ALLY);
@@ -9437,6 +9442,8 @@ void Unit::RemoveFromWorld()
 
         RemoveAreaAurasDueToLeaveWorld();
 
+        RemoveAllFollowers();
+
         if (IsCharmed())
             RemoveCharmedBy(nullptr);
 
diff --git a/src/server/game/Entities/Unit/Unit.h b/src/server/game/Entities/Unit/Unit.h
index f01c476292a..1a910ba48b3 100644
--- a/src/server/game/Entities/Unit/Unit.h
+++ b/src/server/game/Entities/Unit/Unit.h
@@ -20,8 +20,6 @@
 #define __UNIT_H
 
 #include "Object.h"
-#include "FollowerReference.h"
-#include "FollowerRefManager.h"
 #include "CombatManager.h"
 #include "OptionalFwd.h"
 #include "SpellAuraDefines.h"
@@ -61,6 +59,7 @@ enum InventorySlot
     NULL_SLOT                  = 255
 };
 
+struct AbstractFollower;
 struct FactionTemplateEntry;
 struct LiquidData;
 struct LiquidTypeEntry;
@@ -789,7 +788,8 @@ class TC_GAME_API Unit : public WorldObject
         virtual void SetCanDualWield(bool value) { m_canDualWield = value; }
         float GetCombatReach() const override { return m_floatValues[UNIT_FIELD_COMBATREACH]; }
         bool IsWithinCombatRange(Unit const* obj, float dist2compare) const;
-        bool IsWithinMeleeRange(Unit const* obj) const;
+        bool IsWithinMeleeRange(Unit const* obj) const { return IsWithinMeleeRangeAt(GetPosition(), obj); }
+        bool IsWithinMeleeRangeAt(Position const& pos, Unit const* obj) const;
         float GetMeleeRange(Unit const* target) const;
         virtual SpellSchoolMask GetMeleeDamageSchoolMask(WeaponAttackType attackType = BASE_ATTACK, uint8 damageIndex = 0) const = 0;
         uint32 m_extraAttacks;
@@ -1526,8 +1526,9 @@ class TC_GAME_API Unit : public WorldObject
 
         float CalculateSpellpowerCoefficientLevelPenalty(SpellInfo const* spellInfo) const;
 
-        void addFollower(FollowerReference* pRef) { m_FollowingRefManager.insertFirst(pRef); }
-        void removeFollower(FollowerReference* /*pRef*/) { /* nothing to do yet */ }
+        void FollowerAdded(AbstractFollower* f) { m_followingMe.insert(f); }
+        void FollowerRemoved(AbstractFollower* f) { m_followingMe.erase(f); }
+        void RemoveAllFollowers();
 
         MotionMaster* GetMotionMaster() { return i_motionMaster; }
         MotionMaster const* GetMotionMaster() const { return i_motionMaster; }
@@ -1781,7 +1782,7 @@ class TC_GAME_API Unit : public WorldObject
         friend class ThreatManager;
         ThreatManager m_threatManager;
 
-        FollowerRefManager m_FollowingRefManager;
+        std::unordered_set<AbstractFollower*> m_followingMe;
 
         Unit* m_comboTarget;
         int8 m_comboPoints;