修复MoveBy动作的问题

core/Action/MoveBy.cpp

@@ -14,7 +14,7 @@ void e2d::MoveBy::_init()
 
 	if (_target)
 	{
-		_startPos = _target->getPos();
+		_prevPos = _startPos = _target->getPos();
 	}
 }
 
@@ -24,7 +24,14 @@ void e2d::MoveBy::_update()
 
 	if (_target)
 	{
-		_target->setPos(_startPos + _deltaPos * _delta);
+		Point currentPos = _target->getPos();
+		Vector diff = currentPos - _prevPos;
+		_startPos = _startPos + diff;
+
+		Point newPos = _startPos + (_deltaPos * _delta);
+		_target->setPos(newPos);
+
+		_prevPos = newPos;
 	}
 }
 

core/e2daction.h

@@ -144,6 +144,7 @@ protected:
 
 protected:
 	Point	_startPos;
+	Point	_prevPos;
 	Vector	_deltaPos;
 };