Immediate MovementGenerator idea (for facing splines)

motionmaster_immediate_movement.diff

diff --git a/src/server/game/Movement/MotionMaster.cpp b/src/server/game/Movement/MotionMaster.cpp
index 1c7b362176..1a60e0f91c 100644
--- a/src/server/game/Movement/MotionMaster.cpp
+++ b/src/server/game/Movement/MotionMaster.cpp
@@ -336,6 +336,9 @@ void MotionMaster::Add(MovementGenerator* movement, MovementSlot slot/* = MOTION
         return;
     }
 
+    if (movement->HasFlag(MOVEMENTGENERATOR_FLAG_IMMEDIATE) && movement->HasFlag(MOVEMENTGENERATOR_FLAG_INITIALIZATION_PENDING))
+        movement->Initialize(_owner);
+
     if (HasFlag(MOTIONMASTER_FLAG_DELAYED))
     {
         DelayedActionDefine action = [this, movement, slot]()
@@ -1186,6 +1189,69 @@ void MotionMaster::MoveFormation(Unit* leader, float range, float angle, uint32
     }
 }
 
+class ImmediateMovementGenerator : public MovementGenerator
+{
+public:
+    explicit ImmediateMovementGenerator(std::function<void(Movement::MoveSplineInit& init)>&& initializer, uint32 id) : _splineInit(std::move(initializer)), _pointId(id)
+    {
+        Mode = MOTION_MODE_DEFAULT;
+        Priority = MOTION_PRIORITY_NORMAL;
+        Flags = MOVEMENTGENERATOR_FLAG_INITIALIZATION_PENDING | MOVEMENTGENERATOR_FLAG_IMMEDIATE;
+        BaseUnitState = 0;
+    }
+
+    void Initialize(Unit* owner) override
+    {
+        RemoveFlag(MOVEMENTGENERATOR_FLAG_INITIALIZATION_PENDING);
+        AddFlag(MOVEMENTGENERATOR_FLAG_INITIALIZED);
+
+        Movement::MoveSplineInit init(owner);
+        _splineInit(init);
+        owner->UpdateSplineMovement(init.Launch()); // immediately consume the entire spline
+    }
+
+    void Reset(Unit*) override { }
+    bool Update(Unit*, uint32) override { return true; }
+    void Deactivate(Unit*) override { }
+    void Finalize(Unit* owner, bool, bool) override
+    {
+        SetScriptResult(MovementStopReason::Finished);
+
+        if (Creature* creature = owner->ToCreature())
+            if (creature->AI())
+                creature->AI()->MovementInform(EFFECT_MOTION_TYPE, _pointId);
+    }
+
+    MovementGeneratorType GetMovementGeneratorType() const override { return EFFECT_MOTION_TYPE; }
+
+private:
+    std::function<void(Movement::MoveSplineInit& init)> _splineInit;
+    uint32 _pointId;
+};
+
+void MotionMaster::MoveFace(MovementFacingTarget const& facing, uint32 id)
+{
+    std::function<void(Movement::MoveSplineInit& init)> splineInit = [& /*safe, invoked imediately*/](Movement::MoveSplineInit& init)
+    {
+        bool transport = _owner->GetTransport() != nullptr;
+
+        if (!_owner->movespline->Finalized() && _owner->movespline->onTransport == transport)
+            init.MoveTo(_owner->movespline->ComputePosition(), false);
+        else if (!transport)
+            init.MoveTo(PositionToVector3(_owner->GetPosition()), false);
+        else
+            init.MoveTo(PositionToVector3(_owner->m_movementInfo.transport.pos), false);
+
+        if (transport)
+            init.DisableTransportPathTransformations(); // It makes no sense to target global orientation
+
+        std::visit(Movement::MoveSplineInitFacingVisitor(init), facing);
+    };
+
+    // new MovementGenerator object is created to ensure proper lifecycle of the previous generator, deactivating/reactivating it
+    Add(new ImmediateMovementGenerator(std::move(splineInit), id));
+}
+
 void MotionMaster::LaunchMoveSpline(std::function<void(Movement::MoveSplineInit& init)>&& initializer, uint32 id/*= 0*/, MovementGeneratorPriority priority/* = MOTION_PRIORITY_NORMAL*/, MovementGeneratorType type/*= EFFECT_MOTION_TYPE*/)
 {
     if (IsInvalidMovementGeneratorType(type))
@@ -1339,8 +1405,17 @@ void MotionMaster::DirectAdd(MovementGenerator* movement, MovementSlot slot/* =
             else
                 _defaultGenerator->Deactivate(_owner);
 
-            _generators.emplace(movement);
-            AddBaseUnitState(movement);
+            if (!movement->HasFlag(MOVEMENTGENERATOR_FLAG_IMMEDIATE))
+            {
+                _generators.emplace(movement);
+                AddBaseUnitState(movement);
+            }
+            else
+            {
+                movement->Finalize(_owner, true, true);
+                delete movement;
+            }
+
             break;
         default:
             break;
diff --git a/src/server/game/Movement/MovementGenerator.h b/src/server/game/Movement/MovementGenerator.h
index e677d65bb3..51cc7eb648 100755
--- a/src/server/game/Movement/MovementGenerator.h
+++ b/src/server/game/Movement/MovementGenerator.h
@@ -42,6 +42,7 @@ enum MovementGeneratorFlags : uint16
     MOVEMENTGENERATOR_FLAG_INFORM_ENABLED         = 0x080,
     MOVEMENTGENERATOR_FLAG_FINALIZED              = 0x100,
     MOVEMENTGENERATOR_FLAG_PERSIST_ON_DEATH       = 0x200,
+    MOVEMENTGENERATOR_FLAG_IMMEDIATE              = 0x400,
 
     MOVEMENTGENERATOR_FLAG_TRANSITORY = MOVEMENTGENERATOR_FLAG_SPEED_UPDATE_PENDING | MOVEMENTGENERATOR_FLAG_INTERRUPTED
 };