desktop: remove the view-state

There was the "application state", which decided what to show
in the "quadrants" and the "view state" which decided which
quadrant to show. These interacted in a hard-to-grasp way.

The "view state" is used to show the map or dive list in
full screen.

I simply couldn't get these two orthogonal states to interact
properly. Moreover the thing was buggy: If a quadrant was hidden,
the user could still show it, by dragging from the side of the
window, at least under KDE.

To solve these woes, merge the two states into a single
application state. If the widget of a quadrant is set to null,
don't show it. So the four "view states" are now "application
states" where three of the four quadrants are not shown.

This also changes the memory management of the widgets:
widgets that are not shown are now removed from the QSplitter
objects. This makes it possible that the same widget is
shown in *different* quadrants.

While writing this, I stumbled upon a Qt bug, which is known
since 2014:
https://forum.qt.io/topic/43176/qsplitter-sizes-return-0

When restoring the quadrant sizes there was a test whether
the quadrant size is 0. If that was the case, a default size
was set. This seems not to work if the widgets were recently
added. Since this test now always fails, make the quadrants
non-collapsible and thus guarantee that 0 is never saved as
a size.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

4 files changed, 92 insertions, 167 deletions

diff --git a/core/applicationstate.h b/core/applicationstate.h
index 5bae09aa4..c3a8f360d 100644
--- a/core/applicationstate.h
+++ b/core/applicationstate.h
@@ -13,6 +13,10 @@ enum class ApplicationState {
 	EditDiveSite,
 	FilterDive,
 	Statistics,
+	MapMaximized,
+	ProfileMaximized,
+	ListMaximized,
+	InfoMaximized,
 	Count
 };
 
diff --git a/desktop-widgets/mainwindow.cpp b/desktop-widgets/mainwindow.cpp
index 99040aecf..77055b9c1 100644
--- a/desktop-widgets/mainwindow.cpp
+++ b/desktop-widgets/mainwindow.cpp
@@ -125,7 +125,6 @@ MainWindow::MainWindow() : QMainWindow(),
 #ifndef NO_USERMANUAL
 	helpView(0),
 #endif
-	state(VIEWALL),
 	findMovedImagesDialog(nullptr)
 {
 	Q_ASSERT_X(m_Instance == NULL, "MainWindow", "MainWindow recreated!");
@@ -136,6 +135,9 @@ MainWindow::MainWindow() : QMainWindow(),
 	// Define the States of the Application Here, Currently the states are situations where the different
 	// widgets will change on the mainwindow.
 
+	topSplitter = new QSplitter(Qt::Horizontal);
+	bottomSplitter = new QSplitter(Qt::Horizontal);
+
 	// for the "default" mode
 	mainTab.reset(new MainTab);
 	diveList = new DiveListView(this);
@@ -171,7 +173,7 @@ MainWindow::MainWindow() : QMainWindow(),
 	profLayout->addWidget(graphics);
 	profileContainer->setLayout(profLayout);
 
-	diveSiteEdit = new LocationInformationWidget(this);
+	diveSiteEdit.reset(new LocationInformationWidget);
 
 	registerApplicationState(ApplicationState::Default, { { mainTab.get(), FLAG_NONE }, { profileContainer, FLAG_NONE },
 							      { diveList, FLAG_NONE },      { mapWidget, FLAG_NONE } });
@@ -181,12 +183,21 @@ MainWindow::MainWindow() : QMainWindow(),
 							       { &plannerWidgets->plannerSettingsWidget, FLAG_NONE }, { &plannerWidgets->plannerDetails, FLAG_NONE } });
 	registerApplicationState(ApplicationState::EditPlannedDive, { { &plannerWidgets->plannerWidget, FLAG_NONE }, { profileContainer, FLAG_NONE },
 								      { diveList, FLAG_NONE },          { mapWidget, FLAG_NONE } });
-	registerApplicationState(ApplicationState::EditDiveSite, { { diveSiteEdit, FLAG_NONE }, { profileContainer, FLAG_DISABLED },
+	registerApplicationState(ApplicationState::EditDiveSite, { { diveSiteEdit.get(), FLAG_NONE }, { profileContainer, FLAG_DISABLED },
 								   { diveList, FLAG_DISABLED }, { mapWidget, FLAG_NONE } });
 	registerApplicationState(ApplicationState::FilterDive, { { mainTab.get(), FLAG_NONE }, { profileContainer, FLAG_NONE },
 								 { diveList, FLAG_NONE },      { &filterWidget, FLAG_NONE } });
 	registerApplicationState(ApplicationState::Statistics, { { statistics, FLAG_NONE }, { profileContainer, FLAG_NONE },
 								 { diveList, FLAG_DISABLED },   { &filterWidget, FLAG_NONE } });
+	registerApplicationState(ApplicationState::MapMaximized, { { nullptr, FLAG_NONE }, { nullptr, FLAG_NONE },
+								   { nullptr, FLAG_NONE }, { mapWidget, FLAG_NONE } });
+	registerApplicationState(ApplicationState::ProfileMaximized, { { nullptr, FLAG_NONE }, { profileContainer, FLAG_NONE },
+								       { nullptr, FLAG_NONE }, { nullptr, FLAG_NONE } });
+	registerApplicationState(ApplicationState::ListMaximized, { { nullptr, FLAG_NONE },  { nullptr, FLAG_NONE },
+								    { diveList, FLAG_NONE }, { nullptr, FLAG_NONE } });
+	registerApplicationState(ApplicationState::InfoMaximized, { { mainTab.get(), FLAG_NONE }, { nullptr, FLAG_NONE },
+								    { nullptr, FLAG_NONE },       { nullptr, FLAG_NONE } });
+	restoreSplitterSizes();
 	setApplicationState(ApplicationState::Default);
 
 	setWindowIcon(QIcon(":subsurface-icon"));
@@ -367,8 +378,6 @@ void MainWindow::enableDisableOtherDCsActions()
 void MainWindow::setDefaultState()
 {
 	setApplicationState(ApplicationState::Default);
-	if (mainTab->isEditing())
-		ui.bottomLeft->currentWidget()->setEnabled(false);
 }
 
 MainWindow *MainWindow::instance()
@@ -826,52 +835,49 @@ void MainWindow::on_actionYearlyStatistics_triggered()
 	d.exec();
 }
 
-void MainWindow::toggleCollapsible(bool toggle)
-{
-	ui.mainSplitter->setCollapsible(0, toggle);
-	ui.mainSplitter->setCollapsible(1, toggle);
-	ui.topSplitter->setCollapsible(0, toggle);
-	ui.topSplitter->setCollapsible(1, toggle);
-	ui.bottomSplitter->setCollapsible(0, toggle);
-	ui.bottomSplitter->setCollapsible(1, toggle);
-}
-
 void MainWindow::on_actionViewList_triggered()
 {
-	toggleCollapsible(true);
-	beginChangeState(LIST_MAXIMIZED);
-	ui.mainSplitter->setSizes({ COLLAPSED, EXPANDED });
-	showFilterIfEnabled();
+	setApplicationState(ApplicationState::ListMaximized);
 }
 
 void MainWindow::on_actionViewProfile_triggered()
 {
-	toggleCollapsible(true);
-	beginChangeState(PROFILE_MAXIMIZED);
-	ui.topSplitter->setSizes({ COLLAPSED, EXPANDED });
-	ui.mainSplitter->setSizes({ EXPANDED, COLLAPSED });
+	setApplicationState(ApplicationState::ProfileMaximized);
 }
 
 void MainWindow::on_actionViewInfo_triggered()
 {
-	toggleCollapsible(true);
-	beginChangeState(INFO_MAXIMIZED);
-	ui.topSplitter->setSizes({ EXPANDED, COLLAPSED });
-	ui.mainSplitter->setSizes({ EXPANDED, COLLAPSED });
+	setApplicationState(ApplicationState::InfoMaximized);
 }
 
 void MainWindow::on_actionViewMap_triggered()
 {
-	toggleCollapsible(true);
-	beginChangeState(MAP_MAXIMIZED);
-	ui.mainSplitter->setSizes({ COLLAPSED, EXPANDED });
-	ui.bottomSplitter->setSizes({ COLLAPSED, EXPANDED });
+	setApplicationState(ApplicationState::MapMaximized);
 }
 
 void MainWindow::on_actionViewAll_triggered()
 {
-	toggleCollapsible(false);
-	beginChangeState(VIEWALL);
+	setApplicationState(ApplicationState::Default);
+}
+
+void MainWindow::saveSplitterSizes()
+{
+	// Only save splitters if all four quadrants are shown
+	if (ui.mainSplitter->count() < 2 || topSplitter->count() < 2 || bottomSplitter->count() < 2)
+		return;
+
+	QSettings settings;
+	settings.beginGroup("MainWindow");
+	settings.setValue("mainSplitter", ui.mainSplitter->saveState());
+	settings.setValue("topSplitter", topSplitter->saveState());
+	settings.setValue("bottomSplitter", bottomSplitter->saveState());
+}
+
+void MainWindow::restoreSplitterSizes()
+{
+	// Only restore splitters if all four quadrants are shown
+	if (ui.mainSplitter->count() < 2 || topSplitter->count() < 2 || bottomSplitter->count() < 2)
+		return;
 
 	const int appH = qApp->desktop()->size().height();
 	const int appW = qApp->desktop()->size().width();
@@ -884,65 +890,14 @@ void MainWindow::on_actionViewAll_triggered()
 	settings.beginGroup("MainWindow");
 	if (settings.value("mainSplitter").isValid()) {
 		ui.mainSplitter->restoreState(settings.value("mainSplitter").toByteArray());
-		ui.topSplitter->restoreState(settings.value("topSplitter").toByteArray());
-		ui.bottomSplitter->restoreState(settings.value("bottomSplitter").toByteArray());
-		if (ui.mainSplitter->sizes().first() == 0 || ui.mainSplitter->sizes().last() == 0)
-			ui.mainSplitter->setSizes(mainSizes);
-		if (ui.topSplitter->sizes().first() == 0 || ui.topSplitter->sizes().last() == 0)
-			ui.topSplitter->setSizes(infoProfileSizes);
-		if (ui.bottomSplitter->sizes().first() == 0 || ui.bottomSplitter->sizes().last() == 0)
-			ui.bottomSplitter->setSizes(listGlobeSizes);
 
+		topSplitter->restoreState(settings.value("topSplitter").toByteArray());
+		bottomSplitter->restoreState(settings.value("bottomSplitter").toByteArray());
 	} else {
 		ui.mainSplitter->setSizes(mainSizes);
-		ui.topSplitter->setSizes(infoProfileSizes);
-		ui.bottomSplitter->setSizes(listGlobeSizes);
-	}
-	ui.mainSplitter->setCollapsible(0, false);
-	ui.mainSplitter->setCollapsible(1, false);
-	ui.topSplitter->setCollapsible(0, false);
-	ui.topSplitter->setCollapsible(1, false);
-	ui.bottomSplitter->setCollapsible(0,false);
-	ui.bottomSplitter->setCollapsible(1,false);
-}
-
-void MainWindow::enterState(CurrentState newState)
-{
-	state = newState;
-	switch (state) {
-	case VIEWALL:
-		on_actionViewAll_triggered();
-		break;
-	case MAP_MAXIMIZED:
-		on_actionViewMap_triggered();
-		break;
-	case INFO_MAXIMIZED:
-		on_actionViewInfo_triggered();
-		break;
-	case LIST_MAXIMIZED:
-		on_actionViewList_triggered();
-		break;
-	case PROFILE_MAXIMIZED:
-		on_actionViewProfile_triggered();
-		break;
-	}
-}
-
-void MainWindow::beginChangeState(CurrentState s)
-{
-	if (state == VIEWALL && state != s) {
-		saveSplitterSizes();
+		topSplitter->setSizes(infoProfileSizes);
+		bottomSplitter->setSizes(listGlobeSizes);
 	}
-	state = s;
-}
-
-void MainWindow::saveSplitterSizes()
-{
-	QSettings settings;
-	settings.beginGroup("MainWindow");
-	settings.setValue("mainSplitter", ui.mainSplitter->saveState());
-	settings.setValue("topSplitter", ui.topSplitter->saveState());
-	settings.setValue("bottomSplitter", ui.bottomSplitter->saveState());
 }
 
 void MainWindow::on_actionPreviousDC_triggered()
@@ -1138,7 +1093,7 @@ void MainWindow::initialUiSetup()
 		restoreState(settings.value("windowState", 0).toByteArray());
 	}
 
-	enterState((CurrentState)settings.value("lastState", 0).toInt());
+	setApplicationState((ApplicationState)settings.value("lastAppState", 0).toInt());
 	settings.endGroup();
 	show();
 }
@@ -1163,9 +1118,8 @@ void MainWindow::writeSettings()
 	settings.setValue("geometry", saveGeometry());
 	settings.setValue("windowState", saveState());
 	settings.setValue("maximized", isMaximized());
-	settings.setValue("lastState", (int)state);
-	if (state == VIEWALL)
-		saveSplitterSizes();
+	settings.setValue("lastState", (int)getAppState());
+	saveSplitterSizes();
 	settings.endGroup();
 }
 
@@ -1593,54 +1547,41 @@ void MainWindow::on_paste_triggered()
 void MainWindow::on_actionFilterTags_triggered()
 {
 	setApplicationState(getAppState() == ApplicationState::FilterDive ? ApplicationState::Default : ApplicationState::FilterDive);
-	if (state == LIST_MAXIMIZED)
-		showFilterIfEnabled();
 }
 
 void MainWindow::on_actionStats_triggered()
 {
 	setApplicationState(getAppState() == ApplicationState::Statistics ? ApplicationState::Default : ApplicationState::Statistics);
-	toggleCollapsible(true);
-	ui.topSplitter->setSizes({ EXPANDED, COLLAPSED });
-	ui.mainSplitter->setSizes({ EXPANDED, EXPANDED });
-	ui.bottomSplitter->setSizes({ EXPANDED, EXPANDED });
 }
 
-void MainWindow::showFilterIfEnabled()
+void MainWindow::registerApplicationState(ApplicationState state, Quadrants q)
 {
-	if (getAppState() == ApplicationState::FilterDive) {
-		const int appW = qApp->desktop()->size().width();
-		QList<int> profileFilterSizes = { round_int(appW * 0.7), round_int(appW * 0.3) };
-		ui.bottomSplitter->setSizes(profileFilterSizes);
-	} else {
-		ui.bottomSplitter->setSizes({ EXPANDED, COLLAPSED });
-	}
+	applicationState[(int)state] = q;
 }
 
-void MainWindow::addWidgets(const Quadrant &q, QStackedWidget *stack)
+void MainWindow::setQuadrantWidget(const Quadrant &q, QSplitter *splitter)
 {
-	if (q.widget && stack->indexOf(q.widget) == -1)
-		stack->addWidget(q.widget);
+	if (q.widget) {
+		splitter->addWidget(q.widget);
+		splitter->setCollapsible(splitter->count() - 1, false);
+		q.widget->setEnabled(!(q.flags & FLAG_DISABLED));
+	}
 }
 
-void MainWindow::registerApplicationState(ApplicationState state, Quadrants q)
+static void clearSplitter(QSplitter *splitter, QWidget *parent)
 {
-	applicationState[(int)state] = q;
-	addWidgets(q.topLeft, ui.topLeft);
-	addWidgets(q.topRight, ui.topRight);
-	addWidgets(q.bottomLeft, ui.bottomLeft);
-	addWidgets(q.bottomRight, ui.bottomRight);
+	// Qt's ownership model is absolutely hare-brained.
+	// To remove a widget from a splitter, you reparent it, which
+	// informs the splitter via a signal. Wow.
+	while (splitter->count() > 0)
+		splitter->widget(0)->setParent(parent);
 }
 
-void MainWindow::setQuadrant(const Quadrant &q, QStackedWidget *stack)
+void MainWindow::clearSplitters()
 {
-	if (q.widget) {
-		stack->setCurrentWidget(q.widget);
-		stack->show();
-		q.widget->setEnabled(!(q.flags & FLAG_DISABLED));
-	} else {
-		stack->hide();
-	}
+	clearSplitter(topSplitter, this);
+	clearSplitter(bottomSplitter, this);
+	clearSplitter(ui.mainSplitter, this);
 }
 
 void MainWindow::setApplicationState(ApplicationState state)
@@ -1648,18 +1589,26 @@ void MainWindow::setApplicationState(ApplicationState state)
 	if (getAppState() == state)
 		return;
 
+	saveSplitterSizes();
+
 	setAppState(state);
 
+	clearSplitters();
 	const Quadrants &quadrants = applicationState[(int)state];
-	setQuadrant(quadrants.topLeft, ui.topLeft);
-	setQuadrant(quadrants.topRight, ui.topRight);
-	setQuadrant(quadrants.bottomLeft, ui.bottomLeft);
-	setQuadrant(quadrants.bottomRight, ui.bottomRight);
-
-	// The statistics view does its own thing with respect to visibility
-	// of quadrants. So in case we leave that state, change to the
-	// original visibility of the quadrants.
-	enterState(this->state);
+	setQuadrantWidget(quadrants.topLeft, topSplitter);
+	setQuadrantWidget(quadrants.topRight, topSplitter);
+	setQuadrantWidget(quadrants.bottomLeft, bottomSplitter);
+	setQuadrantWidget(quadrants.bottomRight, bottomSplitter);
+	if (topSplitter->count() >= 1) {
+		ui.mainSplitter->addWidget(topSplitter);
+		ui.mainSplitter->setCollapsible(ui.mainSplitter->count() - 1, false);
+	}
+	if (bottomSplitter->count() >= 1) {
+		ui.mainSplitter->addWidget(bottomSplitter);
+		ui.mainSplitter->setCollapsible(ui.mainSplitter->count() - 1, false);
+	}
+
+	restoreSplitterSizes();
 }
 
 void MainWindow::showProgressBar()
diff --git a/desktop-widgets/mainwindow.h b/desktop-widgets/mainwindow.h
index 6734eb7bd..ef29e86bb 100644
--- a/desktop-widgets/mainwindow.h
+++ b/desktop-widgets/mainwindow.h
@@ -41,19 +41,6 @@ class LocationInformationWidget;
 class MainWindow : public QMainWindow {
 	Q_OBJECT
 public:
-	enum {
-		COLLAPSED,
-		EXPANDED
-	};
-
-	enum CurrentState {
-		VIEWALL,
-		MAP_MAXIMIZED,
-		INFO_MAXIMIZED,
-		PROFILE_MAXIMIZED,
-		LIST_MAXIMIZED
-	};
-
 	MainWindow();
 	~MainWindow();
 	static MainWindow *instance();
@@ -165,6 +152,8 @@ slots:
 private:
 	Ui::MainWindow ui;
 	FilterWidget filterWidget;
+	QSplitter *topSplitter;
+	QSplitter *bottomSplitter;
 	QAction *actionNextDive;
 	QAction *actionPreviousDive;
 	QAction *undoAction;
@@ -172,7 +161,6 @@ private:
 #ifndef NO_USERMANUAL
 	UserManual *helpView;
 #endif
-	CurrentState state;
 	QString filter_open();
 	QString filter_import();
 	QString filter_import_dive_sites();
@@ -188,15 +176,13 @@ private:
 	void writeSettings();
 	int file_save();
 	int file_save_as();
-	void beginChangeState(CurrentState s);
 	void saveSplitterSizes();
-	void toggleCollapsible(bool toggle);
-	void showFilterIfEnabled();
+	void restoreSplitterSizes();
 	void updateLastUsedDir(const QString &s);
-	void enterState(CurrentState);
+	void clearSplitters();
 	bool filesAsArguments;
 	UpdateManager *updateManager;
-	LocationInformationWidget *diveSiteEdit;
+	std::unique_ptr<LocationInformationWidget> diveSiteEdit;
 
 	bool plannerStateClean();
 	void configureToolbar();
@@ -226,8 +212,8 @@ private:
 	};
 
 	Quadrants applicationState[(size_t)ApplicationState::Count];
-	static void setQuadrant(const Quadrant &, QStackedWidget *);
-	static void addWidgets(const Quadrant &, QStackedWidget *);
+	static void addWidgets(const Quadrant &);
+	void setQuadrantWidget(const Quadrant &q, QSplitter *splitter);
 	void registerApplicationState(ApplicationState state, Quadrants q);
 
 	QMenu *connections;
diff --git a/desktop-widgets/mainwindow.ui b/desktop-widgets/mainwindow.ui
index b7d4b0bf8..7916d5aad 100644
--- a/desktop-widgets/mainwindow.ui
+++ b/desktop-widgets/mainwindow.ui
@@ -32,20 +32,6 @@
       <property name="orientation">
        <enum>Qt::Vertical</enum>
       </property>
-      <widget class="QSplitter" name="topSplitter">
-       <property name="orientation">
-        <enum>Qt::Horizontal</enum>
-       </property>
-       <widget class="QStackedWidget" name="topLeft"/>
-       <widget class="QStackedWidget" name="topRight"/>
-      </widget>
-      <widget class="QSplitter" name="bottomSplitter">
-       <property name="orientation">
-        <enum>Qt::Horizontal</enum>
-       </property>
-       <widget class="QStackedWidget" name="bottomLeft"/>
-       <widget class="QStackedWidget" name="bottomRight"/>
-      </widget>
      </widget>
     </item>
     <item>