File indexing completed on 2024-05-12 04:43:04

 /***************************************************************************
  *   Copyright (C) 2018 by Emmanuel Lepage Vallee                          *
  *   Author : Emmanuel Lepage Vallee <emmanuel.lepage@kde.org>             *
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
  *   it under the terms of the GNU General Public License as published by  *
  *   the Free Software Foundation; either version 3 of the License, or     *
  *   (at your option) any later version.                                   *
  *                                                                         *
  *   This program is distributed in the hope that it will be useful,       *
  *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
  *   GNU General Public License for more details.                          *
  *                                                                         *
  *   You should have received a copy of the GNU General Public License     *
  *   along with this program.  If not, see <http://www.gnu.org/licenses/>. *
  **************************************************************************/
 #ifndef KQUICKITEMVIEWS_CONTINUITY_P_H
 #define KQUICKITEMVIEWS_CONTINUITY_P_H
 
 namespace StateTracker {
 
 class Index;
 
 /**
  * This bare-bone state tracker helps to track the continuity between the
  * ELEMENTS WITH THE SAME PARENT.
  *
  * The use case for this is to prevent the O(N) operation of the list of
  * elements to check if there is missing holes in them. This could be done with
  * simple artmetic on the row of the last child, first child and the number of
  * children, but this would not handle the corner cases where there multiple
  * "holes". It would also not allow to know where the hole(s) are without
  * looping.
  *
  * This may seem overkill to waste memory tracking this, but there is 2 reasons
  * why it isn't such a bad idea:
  *
  *  * Some ViewportStategies need to know this in every frame (fps) of a scroll
  *    operation with tight frame duration deadlines.
  *  * If the viewport loads a full list model, the "N" of "O(N)" can be very
  *    large.
  *
  * @todo This should, once fully implemented, go hand in hand with
  *  StateTracker::Proximity to avoid useless rowCount other overhead in
  *  StateTracker::Content and make methods such as `isActive` reliable.
  *
  * @todo Slicing a StateTracker::Continuity is currently rather expensive. This
  *  can be brought down to "O(N*log(N))" by using double pointers to create
  *  "pages" of a size representative of the total number of elements. However
  *  this will take more memory and has an overhead in itself. It wont be done
  *  unless it is proven to be significantly faster for real-world models.
  */
 class Continuity final
 {
     friend class Index; // Factory, call private API
 
 public:
     Index *first() const;
     Index *last () const;
 
     int size() const;
 
 private:
     explicit Continuity(Index *first);
 
     StateTracker::Index *m_pFirst {nullptr};
     StateTracker::Index *m_pLast  {nullptr};
 
     static void split(StateTracker::Index *at);
     static void merge(StateTracker::Index *one, StateTracker::Index *two);
     static void remove(Index *i);
     static void setContinuity(Index *i, Continuity *c);
     static Continuity *select(StateTracker::Index *i);
 };
 
 }
 
 #endif