Add PdfNavigationStack for forward/back navigation

Works well enough to use, but needs autotests and at least one fix.

Change-Id: I2114b9fb3b5ddf7cfe2106d4a4fbc7d74852c61d
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 162 insertions, 0 deletions

diff --git a/src/pdf/quick/qquickpdfnavigationstack.cpp b/src/pdf/quick/qquickpdfnavigationstack.cpp
new file mode 100644
index 000000000..c19fae735
--- /dev/null
+++ b/src/pdf/quick/qquickpdfnavigationstack.cpp
@@ -0,0 +1,162 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtPDF module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL3$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPLv3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or later as published by the Free
+** Software Foundation and appearing in the file LICENSE.GPL included in
+** the packaging of this file. Please review the following information to
+** ensure the GNU General Public License version 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickpdfnavigationstack_p.h"
+#include <QLoggingCategory>
+
+QT_BEGIN_NAMESPACE
+
+Q_LOGGING_CATEGORY(qLcNav, "qt.pdf.navigationstack")
+
+/*!
+    \qmltype PdfNavigationStack
+    \instantiates QQuickPdfNavigationStack
+    \inqmlmodule QtQuick.Pdf
+    \ingroup pdf
+    \brief History of the pages visited within a PDF Document.
+    \since 5.15
+
+    PdfNavigationStack remembers which pages the user has visited in a PDF
+    document, and provides the ability to traverse backward and forward.
+*/
+
+QQuickPdfNavigationStack::QQuickPdfNavigationStack(QObject *parent)
+    : QObject(parent)
+{
+}
+
+/*!
+    \qmlmethod void PdfNavigationStack::forward()
+
+    Goes back to the page that was being viewed before back() was called, and
+    then emits the \l currentPageJumped() signal.
+
+    If \l currentPage was set by assignment or binding since the last time
+    \l back() was called, the forward() function does nothing, because there is
+    a branch in the timeline which causes the "future" to be lost.
+*/
+void QQuickPdfNavigationStack::forward()
+{
+    if (m_nextHistoryIndex >= m_pageHistory.count())
+        return;
+    bool backAvailableWas = backAvailable();
+    bool forwardAvailableWas = forwardAvailable();
+    m_changing = true;
+    setCurrentPage(m_pageHistory.at(++m_nextHistoryIndex));
+    m_changing = false;
+    emit currentPageJumped(m_currentPage);
+    if (backAvailableWas != backAvailable())
+        emit backAvailableChanged();
+    if (forwardAvailableWas != forwardAvailable())
+        emit forwardAvailableChanged();
+}
+
+/*!
+    \qmlmethod void PdfNavigationStack::back()
+
+    Pops the stack and causes the \l currentPage property to change to the
+    most-recently-viewed page, and then emits the \l currentPageJumped()
+    signal.
+*/
+void QQuickPdfNavigationStack::back()
+{
+    if (m_nextHistoryIndex <= 0)
+        return;
+    bool backAvailableWas = backAvailable();
+    bool forwardAvailableWas = forwardAvailable();
+    m_changing = true;
+    // TODO don't do that when going back after going forward
+    m_pageHistory.append(m_currentPage);
+    setCurrentPage(m_pageHistory.at(--m_nextHistoryIndex));
+    m_changing = false;
+    emit currentPageJumped(m_currentPage);
+    if (backAvailableWas != backAvailable())
+        emit backAvailableChanged();
+    if (forwardAvailableWas != forwardAvailable())
+        emit forwardAvailableChanged();
+}
+
+/*!
+    \qmlproperty int PdfNavigationStack::currentPage
+
+    This property holds the current page that is being viewed.
+
+    It should be set when the viewer's current page changes. Every time this
+    property is set, it pushes the current page number onto the stack, such
+    that the history of pages that have been viewed will grow.
+*/
+void QQuickPdfNavigationStack::setCurrentPage(int currentPage)
+{
+    if (m_currentPage == currentPage)
+        return;
+    bool backAvailableWas = backAvailable();
+    bool forwardAvailableWas = forwardAvailable();
+    if (!m_changing) {
+        if (m_nextHistoryIndex >= 0 && m_nextHistoryIndex < m_pageHistory.count())
+            m_pageHistory.remove(m_nextHistoryIndex, m_pageHistory.count() - m_nextHistoryIndex);
+        m_pageHistory.append(m_currentPage);
+        m_nextHistoryIndex = m_pageHistory.count();
+    }
+    m_currentPage = currentPage;
+    emit currentPageChanged();
+    if (backAvailableWas != backAvailable())
+        emit backAvailableChanged();
+    if (forwardAvailableWas != forwardAvailable())
+        emit forwardAvailableChanged();
+    qCDebug(qLcNav) << "current" << m_currentPage << "history" << m_pageHistory;
+}
+
+bool QQuickPdfNavigationStack::backAvailable() const
+{
+    return m_nextHistoryIndex > 0;
+}
+
+bool QQuickPdfNavigationStack::forwardAvailable() const
+{
+    return m_nextHistoryIndex < m_pageHistory.count();
+}
+
+/*!
+    \qmlsignal PdfNavigationStack::currentPageJumped(int page)
+
+    This signal is emitted when either forward() or back() is called, to
+    distinguish navigational jumps from cases when the \l currentPage property
+    is set by means of a binding or assignment. Contrast with the
+    \c currentPageChanged signal, which is emitted in all cases, and does not
+    include the \c page argument.
+*/
+
+QT_END_NAMESPACE