fix(Core/Creature): Improve chase movement (#17557)

* Update TargetedMovementGenerator.cpp

* Adding Ovahlord as co-author

TIL: you can assign multiple authors to a commit 😛
Co-Authored-By: Ovahlord <18347559+ovahlord@users.noreply.github.com>

* Remove unused variable

* Undo some changes

---------

Co-authored-by: Ovahlord <18347559+ovahlord@users.noreply.github.com>

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

@@ -32,14 +32,31 @@ static bool IsMutualChase(Unit* owner, Unit* target)
     return target->GetVictim() == owner;
 }
 
+inline float GetChaseRange(Unit const* owner, Unit const* target)
+{
+    float hitboxSum = owner->GetCombatReach() + target->GetCombatReach();
+
+    float hoverDelta = owner->GetHoverHeight() - target->GetHoverHeight();
+    if (hoverDelta != 0.0f)
+        return std::sqrt(std::max(hitboxSum * hitboxSum - hoverDelta * hoverDelta, 0.0f));
+
+    return hitboxSum;
+}
+
 template<class T>
 bool ChaseMovementGenerator<T>::PositionOkay(T* owner, Unit* target, Optional<float> maxDistance, Optional<ChaseAngle> angle)
 {
     float const distSq = owner->GetExactDistSq(target);
+
+    // Distance between owner(chaser) and target is greater than the allowed distance.
     if (maxDistance && distSq > G3D::square(*maxDistance))
         return false;
+
+    // owner's relative angle to its target is not within boundaries
     if (angle && !angle->IsAngleOkay(target->GetRelativeAngle(owner)))
         return false;
+
+    // owner cannot see its target
     if (!owner->IsWithinLOSInMap(target))
         return false;
     return true;
@@ -62,10 +79,7 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
         owner->StopMoving();
         _lastTargetPosition.reset();
         if (Creature* cOwner2 = owner->ToCreature())
-        {
             cOwner2->SetCannotReachTarget();
-        }
-
         return true;
     }
 
@@ -78,85 +92,53 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
     Unit* target = i_target.getTarget();
 
     bool const mutualChase = IsMutualChase(owner, target);
-    float const hitboxSum = owner->GetCombatReach() + target->GetCombatReach();
+    float const chaseRange = GetChaseRange(owner, target);
-    float const minTarget = (_range ? _range->MinTolerance : 0.0f) + hitboxSum;
+    float const minTarget = (_range ? _range->MinTolerance : 0.0f) + chaseRange;
-    float const maxRange = _range ? _range->MaxRange + hitboxSum : owner->GetMeleeRange(target); // melee range already includes hitboxes
+    float const maxRange = _range ? _range->MaxRange + chaseRange : owner->GetMeleeRange(target); // melee range already includes hitboxes
-    float const maxTarget = _range ? _range->MaxTolerance + hitboxSum : CONTACT_DISTANCE + hitboxSum;
+    float const maxTarget = _range ? _range->MaxTolerance + chaseRange : CONTACT_DISTANCE + chaseRange;
+
     Optional<ChaseAngle> angle = mutualChase ? Optional<ChaseAngle>() : _angle;
 
+    // periodically check if we're already in the expected range...
     i_recheckDistance.Update(time_diff);
     if (i_recheckDistance.Passed())
     {
-        i_recheckDistance.Reset(100);
+        i_recheckDistance.Reset(400); // Sniffed value
 
         if (i_recalculateTravel && PositionOkay(owner, target, _movingTowards ? maxTarget : Optional<float>(), angle))
         {
-            if (Creature* cOwner2 = owner->ToCreature())
+            if (owner->HasUnitState(UNIT_STATE_CHASE_MOVE) && !target->isMoving() && !mutualChase)
             {
-                cOwner2->SetCannotReachTarget();
-            }
-
                 i_recalculateTravel = false;
                 i_path = nullptr;
-
+                if (Creature* cOwner2 = owner->ToCreature())
+                    cOwner2->SetCannotReachTarget();
                 owner->StopMoving();
                 owner->SetInFront(target);
                 MovementInform(owner);
                 return true;
             }
         }
+    }
 
+    // if we're done moving, we want to clean up
     if (owner->HasUnitState(UNIT_STATE_CHASE_MOVE) && owner->movespline->Finalized())
     {
+        i_recalculateTravel = false;
+        i_path = nullptr;
+        if (Creature* cOwner2 = owner->ToCreature())
+            cOwner2->SetCannotReachTarget();
         owner->ClearUnitState(UNIT_STATE_CHASE_MOVE);
         owner->SetInFront(target);
         MovementInform(owner);
+    }
 
-        if (owner->IsWithinMeleeRange(this->i_target.getTarget()))
+    // if the target moved, we have to consider whether to adjust
+    if (!_lastTargetPosition || target->GetPosition() != _lastTargetPosition.value() || mutualChase != _mutualChase)
     {
-            owner->Attack(this->i_target.getTarget(), true);
+        _lastTargetPosition = target->GetPosition();
-            if (Creature* cOwner2 = owner->ToCreature())
-            {
-                cOwner2->SetCannotReachTarget();
-            }
-        }
-        else if (i_path && i_path->GetPathType() & PATHFIND_INCOMPLETE)
-        {
-            if (Creature* cOwner2 = owner->ToCreature())
-            {
-                cOwner2->SetCannotReachTarget(this->i_target.getTarget()->GetGUID());
-            }
-        }
-
-        i_recalculateTravel = false;
-        i_path = nullptr;
-    }
-
-    if (_lastTargetPosition && i_target->GetPosition() == _lastTargetPosition.value() && mutualChase == _mutualChase)
-        return true;
-
-    _lastTargetPosition = i_target->GetPosition();
-
-    if (PositionOkay(owner, target, maxRange, angle) && !owner->HasUnitState(UNIT_STATE_CHASE_MOVE))
-    {
-        if (Creature* cOwner2 = owner->ToCreature())
-        {
-            cOwner2->SetCannotReachTarget();
-        }
-
-        return true;
-    }
-
-    float tarX, tarY, tarZ;
-    target->GetPosition(tarX, tarY, tarZ);
-
-    bool withinRange = owner->IsInDist(target, maxRange);
-    bool withinLOS   = owner->IsWithinLOS(tarX, tarY, tarZ);
-    bool moveToward  = !(withinRange && withinLOS);
-
         _mutualChase = mutualChase;
-
+        if (owner->HasUnitState(UNIT_STATE_CHASE_MOVE) || !PositionOkay(owner, target, target->isMoving() ? maxTarget : maxRange, angle))
-    if (owner->HasUnitState(UNIT_STATE_CHASE_MOVE))
         {
             // can we get to the target?
             if (cOwner && !target->isInAccessiblePlaceFor(cOwner))
@@ -166,15 +148,42 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
                 i_path = nullptr;
                 return true;
             }
-    }
 
+            // figure out which way we want to move
+            float tarX, tarY, tarZ;
+            target->GetPosition(tarX, tarY, tarZ);
+            bool withinRange = owner->IsInDist(target, maxRange);
+            bool withinLOS = owner->IsWithinLOS(tarX, tarY, tarZ);
+            bool moveToward = !(withinRange && withinLOS);
+
+            // make a new path if we have to...
             if (!i_path || moveToward != _movingTowards)
                 i_path = std::make_unique<PathGenerator>(owner);
             else
                 i_path->Clear();
 
+            // Predict chase destination to keep up with chase target
+            float additionalRange = 0;
+            bool predictDestination = !mutualChase && target->isMoving();
+            if (predictDestination)
+            {
+                UnitMoveType moveType = MOVE_RUN;
+                if (target->CanFly())
+                    moveType = target->HasUnitMovementFlag(MOVEMENTFLAG_BACKWARD) ? MOVE_FLIGHT_BACK : MOVE_FLIGHT;
+                else
+                {
+                    if (target->IsWalking())
+                        moveType = MOVE_WALK;
+                    else
+                        moveType = target->HasUnitMovementFlag(MOVEMENTFLAG_BACKWARD) ? MOVE_RUN_BACK : MOVE_RUN;
+                }
+                float speed = target->GetSpeed(moveType) * 0.5f;
+                additionalRange = owner->GetExactDistSq(target) < G3D::square(speed) ? 0 : speed;
+            }
+
             float x, y, z;
             bool shortenPath;
+
             // if we want to move toward the target and there's no fixed angle...
             if (moveToward && !angle)
             {
@@ -185,15 +194,13 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
             else
             {
                 // otherwise, we fall back to nearpoint finding
-        target->GetNearPoint(owner, x, y, z, (moveToward ? maxTarget : minTarget) - hitboxSum, 0, angle ? target->ToAbsoluteAngle(angle->RelativeAngle) : target->GetAngle(owner));
+                target->GetNearPoint(owner, x, y, z, (moveToward ? maxTarget : minTarget) - chaseRange - additionalRange, 0, angle ? target->ToAbsoluteAngle(angle->RelativeAngle) : target->GetAngle(owner));
                 shortenPath = false;
             }
 
             if (owner->IsHovering())
                 owner->UpdateAllowedPositionZ(x, y, z);
 
-    i_recalculateTravel = true;
-
             bool success = i_path->CalculatePath(x, y, z, forceDest);
             if (!success || i_path->GetPathType() & PATHFIND_NOPATH)
             {
@@ -202,6 +209,7 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
                     cOwner->SetCannotReachTarget(target->GetGUID());
                 }
 
+                owner->StopMoving();
                 return true;
             }
 
@@ -219,8 +227,7 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
                 switch (cOwner->GetMovementTemplate().GetChase())
                 {
                 case CreatureChaseMovementType::CanWalk:
-                if (owner->IsWalking())
+                    walk = owner->IsWalking();
-                    walk = true;
                     break;
                 case CreatureChaseMovementType::AlwaysWalk:
                     walk = true;
@@ -231,12 +238,15 @@ bool ChaseMovementGenerator<T>::DoUpdate(T* owner, uint32 time_diff)
             }
 
             owner->AddUnitState(UNIT_STATE_CHASE_MOVE);
+            i_recalculateTravel = true;
 
             Movement::MoveSplineInit init(owner);
             init.MovebyPath(i_path->GetPath());
             init.SetFacing(target);
             init.SetWalk(walk);
             init.Launch();
+        }
+    }
 
     return true;
 }
@@ -256,8 +266,8 @@ void ChaseMovementGenerator<Creature>::DoInitialize(Creature* owner)
 {
     i_path = nullptr;
     _lastTargetPosition.reset();
+    i_recheckDistance.Reset(0);
     owner->SetWalk(false);
-    owner->StopMoving();
     owner->AddUnitState(UNIT_STATE_CHASE);
 }