toggle the menubar with single Alt key press (auto hide)

src/controllers/keyboard/keyboardeventfilter.cpp

@@ -11,6 +11,9 @@ KeyboardEventFilter::KeyboardEventFilter(ConfigObject<ConfigValueKbd>* pKbdConfi
         QObject* parent,
         const char* name)
         : QObject(parent),
+#ifndef __APPLE__
+          m_altPressedWithoutKey(false),
+#endif
           m_pKbdConfigObject(nullptr) {
     setObjectName(name);
     setKeyboardConfig(pKbdConfigObject);
@@ -42,6 +45,9 @@ bool KeyboardEventFilter::eventFilter(QObject*, QEvent* e) {
 
         QKeySequence ks = getKeySeq(ke);
         if (!ks.isEmpty()) {
+#ifndef __APPLE__
+            m_altPressedWithoutKey = false;
+#endif
             ConfigValueKbd ksv(ks);
             // Check if a shortcut is defined
             bool result = false;
@@ -68,10 +74,33 @@ bool KeyboardEventFilter::eventFilter(QObject*, QEvent* e) {
                 }
             }
             return result;
+#ifndef __APPLE__
+        } else {
+            // getKeySeq() returns empty string if the press was a modifier only
+            if ((ke->modifiers() & Qt::AltModifier) && !m_altPressedWithoutKey) {
+                // on Linux pressing Alt sends Alt+Qt::Key_Alt, so checking for
+                // Alt modifier is sufficient.
+                // Activate this in case there are issues on Windows
+                // || ke->key() == Qt::Key_Alt) {
+                m_altPressedWithoutKey = true;
+            }
+#endif
         }
     } else if (e->type() == QEvent::KeyRelease) {
         QKeyEvent* ke = (QKeyEvent*)e;
 
+#ifndef __APPLE__
+        // QAction hotkeys are consumed by the object that created them, e.g.
+        // WMainMenuBar, so we will not receive menu hotkey keypress events here.
+        // However, it may happen that we receive a RELEASE event for an Alt+key
+        // combo for which no KEYPRESS was registered.
+        // So react only to Alt-only releases.
+        if (m_altPressedWithoutKey && ke->key() == Qt::Key_Alt) {
+            emit altPressedWithoutKeys();
+        }
+        m_altPressedWithoutKey = false;
+#endif
+
 #ifdef __APPLE__
         // On Mac OSX the nativeScanCode is empty
         int keyId = ke->key();
@@ -120,28 +149,38 @@ bool KeyboardEventFilter::eventFilter(QObject*, QEvent* e) {
 
 // static
 QKeySequence KeyboardEventFilter::getKeySeq(QKeyEvent* e) {
-    if (e->key() >= 0x01000020 && e->key() <= 0x01000023) {
-        // Do not act on Modifier only, avoid returning "khmer vowel sign ie (U+17C0)"
-        return {};
+    QKeySequence k;
+
+    if ((e->key() >= Qt::Key_Shift && e->key() <= Qt::Key_Alt) ||
+            e->key() == Qt::Key_AltGr) {
+        // Do not act on Modifier only, Shift, Ctrl, Meta, Alt and AltGr
+        // avoid returning "khmer vowel sign ie (U+17C0)"
+        return k;
+    }
+
+    QString modseq;
+    // TODO(XXX) check if we may simply return QKeySequence(e->modifiers()+e->key())
+
+    if (e->modifiers() & Qt::ShiftModifier) {
+        modseq += "Shift+";
     }
 
+    if (e->modifiers() & Qt::ControlModifier) {
+        modseq += "Ctrl+";
+    }
+
+    if (e->modifiers() & Qt::AltModifier) {
+        modseq += "Alt+";
+    }
+
+    if (e->modifiers() & Qt::MetaModifier) {
+        modseq += "Meta+";
+    }
+
+    QString keyseq = QKeySequence(e->key()).toString();
+    k = QKeySequence(modseq + keyseq);
+
     if (CmdlineArgs::Instance().getDeveloper()) {
-        QString modseq;
-        QKeySequence k;
-        if (e->modifiers() & Qt::ShiftModifier) {
-            modseq += "Shift+";
-        }
-        if (e->modifiers() & Qt::ControlModifier) {
-            modseq += "Ctrl+";
-        }
-        if (e->modifiers() & Qt::AltModifier) {
-            modseq += "Alt+";
-        }
-        if (e->modifiers() & Qt::MetaModifier) {
-            modseq += "Meta+";
-        }
-        QString keyseq = QKeySequence(e->key()).toString();
-        k = QKeySequence(modseq + keyseq);
         if (e->type() == QEvent::KeyPress) {
             qDebug() << "keyboard press: " << k.toString();
         } else if (e->type() == QEvent::KeyRelease) {

src/controllers/keyboard/keyboardeventfilter.h

@@ -28,6 +28,11 @@ class KeyboardEventFilter : public QObject {
     // Returns a valid QString with modifier keys from a QKeyEvent
     static QKeySequence getKeySeq(QKeyEvent* e);
 
+#ifndef __APPLE__
+  signals:
+    void altPressedWithoutKeys();
+#endif
+
   private:
     struct KeyDownInformation {
         KeyDownInformation(int keyId, int modifiers, ControlObject* pControl)
@@ -41,6 +46,10 @@ class KeyboardEventFilter : public QObject {
         ControlObject* pControl;
     };
 
+#ifndef __APPLE__
+    bool m_altPressedWithoutKey;
+#endif
+
     // Run through list of active keys to see if the pressed key is already active
     // and is not a control that repeats when held.
     bool shouldSkipHeldKey(int keyId) {

src/mixxxmainwindow.cpp

@@ -1,5 +1,6 @@
 #include "mixxxmainwindow.h"
 
+#include <QCheckBox>
 #include <QCloseEvent>
 #include <QDebug>
 #include <QFileDialog>
@@ -81,6 +82,9 @@ inline bool supportsGlobalMenu() {
     return false;
 }
 #endif
+
+const ConfigKey kHideMenuBarConfigKey = ConfigKey("[Config]", "hide_menubar");
+const ConfigKey kMenuBarHintConfigKey = ConfigKey("[Config]", "show_menubar_hint");
 } // namespace
 
 MixxxMainWindow::MixxxMainWindow(std::shared_ptr<mixxx::CoreServices> pCoreServices)
@@ -302,8 +306,15 @@ void MixxxMainWindow::initialize() {
             this,
             &MixxxMainWindow::rebootMixxxView,
             Qt::DirectConnection);
+#ifndef __APPLE__
+    connect(m_pPrefDlg,
+            &DlgPreferences::menuBarAutoHideChanged,
+            this,
+            &MixxxMainWindow::slotUpdateMenuBarAltKeyConnection,
+            Qt::DirectConnection);
+#endif
 
-    // Connect signals to the menubar. Should be done before emit newSkinLoaded.
+    // Connect signals to the menubar. Should be done before emit skinLoaded.
     connectMenuBar();
 
     QWidget* oldWidget = m_pCentralWidget;
@@ -369,6 +380,21 @@ void MixxxMainWindow::initialize() {
     // corrupted. See bug 521509 -- bkgood ?? -- vrince
     setCentralWidget(m_pCentralWidget);
 
+#ifndef __APPLE__
+    // Ask for permission to auto-hide the menu bar if applicable.
+#ifdef __LINUX__
+    // This makes no sense when starting in windowed mode with a global menu,
+    // we'll ask when going fullscreen.
+    if (!m_supportsGlobalMenuBar || isFullScreen()) {
+        alwaysHideMenuBarDlg();
+        slotUpdateMenuBarAltKeyConnection();
+    }
+#else
+    alwaysHideMenuBarDlg();
+    slotUpdateMenuBarAltKeyConnection();
+#endif
+#endif
+
     // Show the menubar after the launch image is replaced by the skin widget,
     // otherwise it would shift the launch image shortly before the skin is visible.
     m_pMenuBar->show();
@@ -527,6 +553,51 @@ void MixxxMainWindow::initializeWindow() {
     slotUpdateWindowTitle(TrackPointer());
 }
 
+#ifndef __APPLE__
+void MixxxMainWindow::alwaysHideMenuBarDlg() {
+    if (!m_pCoreServices->getSettings()->getValue<bool>(
+                kMenuBarHintConfigKey, true)) {
+        return;
+    }
+    QString title = tr("Allow Mixxx to hide the menu bar?");
+    //: Always show the menu bar?
+    QString hideBtnLabel = tr("Hide");
+    QString showBtnLabel = tr("Always show");
+    //: Keep formatting tags <b> (bold text) and <br> (linebreak).
+    //: %1 is the placeholder for the 'Always show' button label
+    QString desc = tr(
+            "The Mixxx menu bar is hidden and can be toggled with a single press "
+            "of the <b>Alt</b> key.<br><br>"
+            "Click <b>%1</b> to agree.<br><br>"
+            "Click <b>%2</b> to disable that, for example if you don't use Mixxx "
+            "with a keyboard.<br><br>"
+            "You can change this setting any time in Preferences -> Interface."
+            "<br>") // line break for some extra margin to the checkbox
+                           .arg(hideBtnLabel, showBtnLabel);
+
+    QMessageBox msg;
+    msg.setIcon(QMessageBox::Question);
+    msg.setWindowTitle(title);
+    msg.setText(desc);
+    QCheckBox askAgainCheckBox;
+    askAgainCheckBox.setText(tr("Ask me again"));
+    askAgainCheckBox.setCheckState(Qt::Checked);
+    msg.setCheckBox(&askAgainCheckBox);
+    QPushButton* pHideBtn = msg.addButton(hideBtnLabel, QMessageBox::AcceptRole);
+    QPushButton* pShowBtn = msg.addButton(showBtnLabel, QMessageBox::RejectRole);
+    msg.setDefaultButton(pShowBtn);
+    msg.exec();
+
+    m_pCoreServices->getSettings()->setValue(
+            kMenuBarHintConfigKey,
+            askAgainCheckBox.checkState() == Qt::Checked ? 1 : 0);
+
+    m_pCoreServices->getSettings()->setValue(
+            kHideMenuBarConfigKey,
+            msg.clickedButton() == pHideBtn ? 1 : 0);
+}
+#endif
+
 QDialog::DialogCode MixxxMainWindow::soundDeviceErrorDlg(
         const QString &title, const QString &text, bool* retryClicked) {
     QMessageBox msgBox;
@@ -885,6 +956,29 @@ void MixxxMainWindow::connectMenuBar() {
 #endif
 }
 
+#ifndef __APPLE__
+void MixxxMainWindow::slotUpdateMenuBarAltKeyConnection() {
+    if (!m_pCoreServices->getKeyboardEventFilter() || !m_pMenuBar) {
+        return;
+    }
+
+    if (m_pCoreServices->getSettings()->getValue<bool>(kHideMenuBarConfigKey, false)) {
+        connect(m_pCoreServices->getKeyboardEventFilter().get(),
+                &KeyboardEventFilter::altPressedWithoutKeys,
+                m_pMenuBar,
+                &WMainMenuBar::slotToggleMenuBar,
+                Qt::UniqueConnection);
+        m_pMenuBar->hideMenuBar();
+    } else {
+        disconnect(m_pCoreServices->getKeyboardEventFilter().get(),
+                &KeyboardEventFilter::altPressedWithoutKeys,
+                m_pMenuBar,
+                &WMainMenuBar::slotToggleMenuBar);
+        m_pMenuBar->showMenuBar();
+    }
+}
+#endif
+
 void MixxxMainWindow::slotFileLoadSongPlayer(int deck) {
     QString group = PlayerManager::groupForDeck(deck - 1);
 
@@ -1212,6 +1306,10 @@ bool MixxxMainWindow::eventFilter(QObject* obj, QEvent* event) {
                 QApplication::setAttribute(Qt::AA_DontUseNativeMenuBar, isFullScreenNow);
                 createMenuBar();
                 connectMenuBar();
+                // With a global menu we didn't show the menubar auto-hide dialog
+                // during (windowed) startup, so ask now.
+                alwaysHideMenuBarDlg();
+                slotUpdateMenuBarAltKeyConnection();
             }
 #endif
             // This will toggle the Fullscreen checkbox and hide the menubar if

src/mixxxmainwindow.h

@@ -78,6 +78,11 @@ class MixxxMainWindow : public QMainWindow {
     void slotNoAuxiliaryInputConfigured();
     void slotNoDeckPassthroughInputConfigured();
     void slotNoVinylControlInputConfigured();
+#ifndef __APPLE__
+    /// Update whether the menubar is toggled pressing the Alt key and show/hide
+    /// it accordingly
+    void slotUpdateMenuBarAltKeyConnection();
+#endif
 
     void initializationProgressUpdate(int progress, const QString& serviceName);
 
@@ -105,6 +110,10 @@ class MixxxMainWindow : public QMainWindow {
     void tryParseAndSetDefaultStyleSheet();
 
     bool confirmExit();
+#ifndef __APPLE__
+    void alwaysHideMenuBarDlg();
+#endif
+
     QDialog::DialogCode soundDeviceErrorDlg(
             const QString &title, const QString &text, bool* retryClicked);
     QDialog::DialogCode soundDeviceBusyDlg(bool* retryClicked);

src/preferences/dialog/dlgpreferences.cpp

@@ -147,6 +147,11 @@ DlgPreferences::DlgPreferences(
             this,
             &DlgPreferences::reloadUserInterface,
             Qt::DirectConnection);
+    connect(pInterfacePage,
+            &DlgPrefInterface::menuBarAutoHideChanged,
+            this,
+            &DlgPreferences::menuBarAutoHideChanged,
+            Qt::DirectConnection);
     addPageWidget(PreferencesPage(pInterfacePage,
                           new QTreeWidgetItem(
                                   contentsTreeWidget, QTreeWidgetItem::Type)),

src/preferences/dialog/dlgpreferences.h

@@ -75,9 +75,9 @@ class DlgPreferences : public QDialog, public Ui::DlgPreferencesDlg {
     // Emitted if the user clicks Reset to Defaults.
     void resetToDefaults();
 
-  signals:
     void reloadUserInterface();
     void tooltipModeChanged(mixxx::TooltipsPreference tooltipMode);
+    void menuBarAutoHideChanged();
 
   protected:
     bool eventFilter(QObject*, QEvent*);

src/preferences/dialog/dlgprefinterface.cpp

@@ -34,6 +34,11 @@ const QString kResizableSkinKey = QStringLiteral("ResizableSkin");
 const QString kLocaleKey = QStringLiteral("Locale");
 const QString kTooltipsKey = QStringLiteral("Tooltips");
 const QString kMultiSamplingKey = QStringLiteral("multi_sampling");
+const QString kHideMenuBarKey = QStringLiteral("hide_menubar");
+
+// TODO move these to a common *_defs.h file, some are also used by e.g. MixxxMainWindow
+const bool kStartInFullscreenDefault = false;
+const bool kHideMenuBarDefault = true;
 
 } // namespace
 
@@ -301,7 +306,10 @@ void DlgPrefInterface::slotUpdate() {
     spinBoxScaleFactor->setMinimum(m_minScaleFactor * 100);
 
     checkBoxStartFullScreen->setChecked(m_pConfig->getValue(
-            ConfigKey(kConfigGroup, kStartInFullscreenKey), false));
+            ConfigKey(kConfigGroup, kStartInFullscreenKey), kStartInFullscreenDefault));
+
+    checkBoxHideMenuBar->setChecked(m_pConfig->getValue(
+            ConfigKey(kConfigGroup, kHideMenuBarKey), kHideMenuBarDefault));
 
     loadTooltipPreferenceFromConfig();
 
@@ -324,7 +332,12 @@ void DlgPrefInterface::slotResetToDefaults() {
     spinBoxScaleFactor->setValue(100);
 
     // Don't start in full screen.
-    checkBoxStartFullScreen->setChecked(false);
+    checkBoxStartFullScreen->setChecked(kStartInFullscreenDefault);
+
+    // Always show the menu bar
+    checkBoxHideMenuBar->setChecked(kHideMenuBarDefault);
+    // Also show the menu bar hint again on next start?
+    // Use bool member to set [Config],show_menubar_hint to 1 in slotApply()
 
     // Inhibit the screensaver
     comboBoxScreensaver->setCurrentIndex(comboBoxScreensaver->findData(
@@ -442,6 +455,10 @@ void DlgPrefInterface::slotApply() {
     m_pConfig->set(ConfigKey(kConfigGroup, kStartInFullscreenKey),
             ConfigValue(checkBoxStartFullScreen->isChecked()));
 
+    m_pConfig->set(ConfigKey(kConfigGroup, kHideMenuBarKey),
+            ConfigValue(checkBoxHideMenuBar->isChecked()));
+    emit menuBarAutoHideChanged();
+
     m_pConfig->set(ConfigKey(kControlsGroup, kTooltipsKey),
             ConfigValue(static_cast<int>(m_tooltipMode)));
     emit tooltipModeChanged(m_tooltipMode);

src/preferences/dialog/dlgprefinterface.h

@@ -44,6 +44,7 @@ class DlgPrefInterface : public DlgPreferencePage, public Ui::DlgPrefControlsDlg
 
   signals:
     void reloadUserInterface();
+    void menuBarAutoHideChanged();
     void tooltipModeChanged(mixxx::TooltipsPreference tooltipMode);
 
   private: