Core/Movement:

*cyclic movement will now always use catmullrom and enter_cycle flags. Fixes visual issues when spline gets sent via update_object packet
*MoveCirclePath motion master will now always make the creature fly. According to sniffs all cyclic moving creatures are flying
*remove hack from cyclic monster_move packet. The first vertex is getting deleted by the client when using enter_cycle spline flag.
*recalculate cycle path when completing first loop to get rid of the first vertex
*implement SMSG_FLIGHT_SPLINE_SYNC opcode. according to sniffs this opcode gets sent every 5 seconds to fix client / server asynch movement issues. thx to Morgoporc for the unit.cpp part

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

@@ -486,20 +486,38 @@ void Unit::MonsterMoveWithSpeed(float x, float y, float z, float speed, bool gen
     init.Launch();
 }
 
-void Unit::UpdateSplineMovement(uint32 t_diff)
+void Unit::UpdateSplineMovement(uint32 p_diff)
 {
+    uint32 const flightSplineSyncDelay = 5 * TimeConstants::IN_MILLISECONDS;
+
+    bool arrived = movespline->Finalized();
     if (movespline->Finalized())
         return;
 
-    movespline->updateState(t_diff);
-    bool arrived = movespline->Finalized();
+    movespline->updateState(p_diff);
+    arrived = movespline->Finalized();
 
     if (arrived)
         DisableSpline();
 
-    m_movesplineTimer.Update(t_diff);
+    m_movesplineTimer.Update(p_diff);
     if (m_movesplineTimer.Passed() || arrived)
         UpdateSplinePosition();
+
+    m_FlightSplineSyncTimer.Update(p_diff);
+    if (m_FlightSplineSyncTimer.Passed())
+    {
+        float percent = 1.0f;
+        float totalTime = movespline->Duration();
+        if (totalTime > 0.0f)
+            percent = (float)movespline->timePassed() / totalTime;
+
+        // Synch flight movement for cylic movement
+        if (movespline->isCyclic() && IsFlying())
+            SendFlightSplineSync(percent);
+
+        m_FlightSplineSyncTimer.Reset(flightSplineSyncDelay);
+    }
 }
 
 void Unit::UpdateSplinePosition()
@@ -8984,6 +9002,14 @@ void Unit::SetSpeedRate(UnitMoveType mtype, float rate)
     Movement::PacketSender(this, moveTypeToOpcode[mtype][0], moveTypeToOpcode[mtype][1], moveTypeToOpcode[mtype][2], &extra).Send();
 }
 
+void Unit::SendFlightSplineSync(float splineDist)
+{
+    WorldPacket data(SMSG_FLIGHT_SPLINE_SYNC, 11);
+    data << float(splineDist);
+    data.appendPackGUID(GetGUID());
+    SendMessageToSet(&data, false);
+}
+
 void Unit::setDeathState(DeathState s)
 {
     // Death state needs to be updated before RemoveAllAurasOnDeath() is called, to prevent entering combat