ChangedStateItemDelegate.h

/*
    Scan Tailor - Interactive post-processing tool for scanned pages.
    Copyright (C) 2007-2009  Joseph Artsimovich <joseph_a@mail.ru>

    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 CHANGEDSTATEITEMDELEGATE_H_
#define CHANGEDSTATEITEMDELEGATE_H_

#include <QStyle>
#include <QStyleOptionViewItem>
#include <QStyledItemDelegate>

/**
 * \brief A decoration of an existing item delegate
 *        that forces certain item states.
 */
template <typename T = QStyledItemDelegate>
class ChangedStateItemDelegate : public T {
 public:
  explicit ChangedStateItemDelegate(QObject* parent = nullptr) : T(parent), m_changedFlags(), m_changedMask() {}

  void flagsForceEnabled(QStyle::State flags) {
    m_changedFlags |= flags;
    m_changedMask |= flags;
  }

  void flagsForceDisabled(QStyle::State flags) {
    m_changedFlags &= ~flags;
    m_changedMask |= flags;
  }

  void removeChanges(QStyle::State remove) { m_changedMask &= ~remove; }

  void removeAllChanges() { m_changedMask = QStyle::State(); }

  virtual void paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const {
    const QStyle::State orig_state = option.state;

    const QStyle::State new_state = (orig_state & ~m_changedMask) | (m_changedFlags & m_changedMask);

    // Evil but necessary: the alternative solution of modifying
    // a copy doesn't work, as option doesn't really point to
    // QStyleOptionViewItem, but to one of its subclasses.
    QStyleOptionViewItem& non_const_opt = const_cast<QStyleOptionViewItem&>(option);

    non_const_opt.state = new_state;
    T::paint(painter, non_const_opt, index);
    non_const_opt.state = orig_state;
  }

 private:
  QStyle::State m_changedFlags;
  QStyle::State m_changedMask;
};


#endif  // ifndef CHANGEDSTATEITEMDELEGATE_H_