The following stealth changes are implemented.

- Combat no longer removes stealth, only damage does
 - Creatures will pursue a stealthed unit they cannot see if they're already in combat with them
 - When a player is ~~3 yards~~ 8% + 1.5 yards away from the usual stealth detection distance, the creature will perform the "alerted" effect.
 - When sitting/sleeping creatures are distracted or alerted, they will stand up
 - Idle movement creatures will return to their original (spawn) orientation after distract/alert
 - When entering combat with a distracted/alerted creature, distract state is removed
 - NPC no longer have a limit to stealth visibility (granted by stealth modifier spells/buffs)
 - If alert visibility is greater than aggro range, no alert sent

src/server/game/Entities/Object/Object.cpp

@@ -1539,7 +1539,7 @@ float WorldObject::GetSightRange(const WorldObject* target) const
     return 0.0f;
 }
 
-bool WorldObject::CanSeeOrDetect(WorldObject const* obj, bool ignoreStealth, bool distanceCheck) const
+bool WorldObject::CanSeeOrDetect(WorldObject const* obj, bool ignoreStealth, bool distanceCheck, bool checkAlert) const
 {
     if (this == obj)
         return true;
@@ -1611,7 +1611,7 @@ bool WorldObject::CanSeeOrDetect(WorldObject const* obj, bool ignoreStealth, boo
     if (obj->IsInvisibleDueToDespawn())
         return false;
 
-    if (!CanDetect(obj, ignoreStealth))
+    if (!CanDetect(obj, ignoreStealth, checkAlert))
         return false;
 
     return true;
@@ -1622,7 +1622,7 @@ bool WorldObject::CanNeverSee(WorldObject const* obj) const
     return GetMap() != obj->GetMap() || !InSamePhase(obj);
 }
 
-bool WorldObject::CanDetect(WorldObject const* obj, bool ignoreStealth) const
+bool WorldObject::CanDetect(WorldObject const* obj, bool ignoreStealth, bool checkAlert) const
 {
     const WorldObject* seer = this;
 
@@ -1637,7 +1637,7 @@ bool WorldObject::CanDetect(WorldObject const* obj, bool ignoreStealth) const
     if (!ignoreStealth && !seer->CanDetectInvisibilityOf(obj))
         return false;
 
-    if (!ignoreStealth && !seer->CanDetectStealthOf(obj))
+    if (!ignoreStealth && !seer->CanDetectStealthOf(obj, checkAlert))
         return false;
 
     return true;
@@ -1674,7 +1674,7 @@ bool WorldObject::CanDetectInvisibilityOf(WorldObject const* obj) const
     return true;
 }
 
-bool WorldObject::CanDetectStealthOf(WorldObject const* obj) const
+bool WorldObject::CanDetectStealthOf(WorldObject const* obj, bool checkAlert) const
 {
     // Combat reach is the minimal distance (both in front and behind),
     //   and it is also used in the range calculation.
@@ -1724,9 +1724,19 @@ bool WorldObject::CanDetectStealthOf(WorldObject const* obj) const
         // Calculate max distance
         float visibilityRange = float(detectionValue) * 0.3f + combatReach;
 
-        if (visibilityRange > MAX_PLAYER_STEALTH_DETECT_RANGE)
+        // If this unit is an NPC then player detect range doesn't apply
+        if (unit && unit->GetTypeId() == TYPEID_PLAYER && visibilityRange > MAX_PLAYER_STEALTH_DETECT_RANGE)
             visibilityRange = MAX_PLAYER_STEALTH_DETECT_RANGE;
 
+        // When checking for alert state, look 8% further, and then 1.5 yards more than that.
+        if (checkAlert)
+            visibilityRange += (visibilityRange * 0.08f) + 1.5f;
+
+        // If checking for alert, and creature's visibility range is greater than aggro distance, No alert
+        Unit const* tunit = obj->ToUnit();
+        if (checkAlert && unit && unit->ToCreature() && visibilityRange >= unit->ToCreature()->GetAttackDistance(tunit) + unit->ToCreature()->m_CombatDistance)
+            return false;
+
         if (distance > visibilityRange)
             return false;
     }