Add API to send native desktop notifications to QgsNative

And use native desktop notifications on Linux (via dbus). Avoids
unnecessary system tray icon creation, which is a pre-requisite
for the Qt desktop notification implemention. This should avoid
annoying notifications on certain Linux desktop environments,
and should also allow us to use prettier Windows notifications
(when implemented!)

src/app/qgisapp.cpp

@@ -94,6 +94,9 @@
 #include "processing/qgs3dalgorithms.h"
 #endif
 
+#include "qgsgui.h"
+#include "qgsnative.h"
+
 #include <QNetworkReply>
 #include <QNetworkProxy>
 #include <QAuthenticator>
@@ -707,9 +710,12 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipVersionCh
   }
   endProfile();
 
-  mTray = new QSystemTrayIcon();
-  mTray->setIcon( QIcon( QgsApplication::appIconPath() ) );
-  mTray->hide();
+  if ( !( QgsGui::nativePlatformInterface()->capabilities() & QgsNative::NativeDesktopNotifications ) )
+  {
+    mTray = new QSystemTrayIcon();
+    mTray->setIcon( QIcon( QgsApplication::appIconPath() ) );
+    mTray->hide();
+  }
 
   // Create the themes folder for the user
   startProfile( QStringLiteral( "Creating theme folder" ) );
@@ -1387,7 +1393,6 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipVersionCh
   {
     mCentralContainer->setCurrentIndex( 0 );
   } );
-
 } // QgisApp ctor
 
 QgisApp::QgisApp()
@@ -13844,13 +13849,34 @@ QMenu *QgisApp::createPopupMenu()
 }
 
 
-void QgisApp::showSystemNotification( const QString &title, const QString &message )
+void QgisApp::showSystemNotification( const QString &title, const QString &message, bool replaceExisting )
 {
-  // Menubar icon is hidden by default. Show to enable notification bubbles
-  mTray->show();
-  mTray->showMessage( title, message );
-  // Re-hide menubar icon
-  mTray->hide();
+  static QVariant sLastMessageId;
+
+  QgsNative::NotificationSettings settings;
+  settings.transient = true;
+  if ( replaceExisting )
+    settings.messageId = sLastMessageId;
+  settings.svgAppIconPath = QgsApplication::iconsPath() + QStringLiteral( "qgis_icon.svg" );
+
+  QgsNative::NotificationResult result = QgsGui::instance()->nativePlatformInterface()->showDesktopNotification( title, message, settings );
+
+  if ( !result.successful )
+  {
+    // fallback - use system tray notification
+    if ( mTray )
+    {
+      // Menubar icon is hidden by default. Show to enable notification bubbles
+      mTray->show();
+      mTray->showMessage( title, message );
+      // Re-hide menubar icon
+      mTray->hide();
+    }
+  }
+  else
+  {
+    sLastMessageId = result.messageId;
+  }
 }
 
 void QgisApp::showStatisticsDockWidget( bool show )

src/app/qgisapp.h

@@ -416,8 +416,9 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
      *
      * \param title
      * \param message
+     * \param replaceExisting set to true to replace any existing notifications, or false to add a new notification
      */
-    void showSystemNotification( const QString &title, const QString &message );
+    void showSystemNotification( const QString &title, const QString &message, bool replaceExisting = true );
 
 
     //! Actions to be inserted in menus and toolbars

src/native/linux/qgslinuxnative.cpp

@@ -21,6 +21,12 @@
 #include <QString>
 #include <QtDBus/QtDBus>
 #include <QtDebug>
+#include <QImage>
+
+QgsNative::Capabilities QgsLinuxNative::capabilities() const
+{
+  return NativeDesktopNotifications;
+}
 
 void QgsLinuxNative::openFileExplorerAndSelectFile( const QString &path )
 {
@@ -41,3 +47,117 @@ void QgsLinuxNative::openFileExplorerAndSelectFile( const QString &path )
     QgsNative::openFileExplorerAndSelectFile( path );
   }
 }
+
+/**
+ * Automatic marshaling of a QImage for org.freedesktop.Notifications.Notify
+ *
+ * This function is from the Clementine project (see
+ * http://www.clementine-player.org) and licensed under the GNU General Public
+ * License, version 3 or later.
+ *
+ * Copyright 2010, David Sansome <me@davidsansome.com>
+ */
+QDBusArgument &operator<<( QDBusArgument &arg, const QImage &image )
+{
+  if ( image.isNull() )
+  {
+    arg.beginStructure();
+    arg << 0 << 0 << 0 << false << 0 << 0 << QByteArray();
+    arg.endStructure();
+    return arg;
+  }
+
+  QImage scaled = image.scaledToHeight( 100, Qt::SmoothTransformation );
+  scaled = scaled.convertToFormat( QImage::Format_ARGB32 );
+
+#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
+  // ABGR -> ARGB
+  QImage i = scaled.rgbSwapped();
+#else
+  // ABGR -> GBAR
+  QImage i( scaled.size(), scaled.format() );
+  for ( int y = 0; y < i.height(); ++y )
+  {
+    QRgb *p = ( QRgb * ) scaled.scanLine( y );
+    QRgb *q = ( QRgb * ) i.scanLine( y );
+    QRgb *end = p + scaled.width();
+    while ( p < end )
+    {
+      *q = qRgba( qGreen( *p ), qBlue( *p ), qAlpha( *p ), qRed( *p ) );
+      p++;
+      q++;
+    }
+  }
+#endif
+
+  arg.beginStructure();
+  arg << i.width();
+  arg << i.height();
+  arg << i.bytesPerLine();
+  arg << i.hasAlphaChannel();
+  int channels = i.isGrayscale() ? 1 : ( i.hasAlphaChannel() ? 4 : 3 );
+  arg << i.depth() / channels;
+  arg << channels;
+  arg << QByteArray( reinterpret_cast<const char *>( i.bits() ), i.numBytes() );
+  arg.endStructure();
+  return arg;
+}
+
+const QDBusArgument &operator>>( const QDBusArgument &arg, QImage & )
+{
+  // This is needed to link but shouldn't be called.
+  Q_ASSERT( 0 );
+  return arg;
+}
+
+QgsNative::NotificationResult QgsLinuxNative::showDesktopNotification( const QString &summary, const QString &body, const NotificationSettings &settings )
+{
+  NotificationResult result;
+  result.successful = false;
+
+  if ( !QDBusConnection::sessionBus().isConnected() )
+  {
+    return result;
+  }
+
+  qDBusRegisterMetaType<QImage>();
+
+  QDBusInterface iface( QStringLiteral( "org.freedesktop.Notifications" ),
+                        QStringLiteral( "/org/freedesktop/Notifications" ),
+                        QStringLiteral( "org.freedesktop.Notifications" ),
+                        QDBusConnection::sessionBus() );
+
+  QVariantMap hints;
+  hints[QStringLiteral( "transient" )] = settings.transient;
+  if ( !settings.image.isNull() )
+    hints[QStringLiteral( "image_data" )] = settings.image;
+
+  QVariantList argumentList;
+  argumentList << "qgis"; //app_name
+  // replace_id
+  if ( settings.messageId.isValid() )
+    argumentList << static_cast< uint >( settings.messageId.toInt() );
+  else
+    argumentList << static_cast< uint >( 0 );
+  // app_icon
+  if ( !settings.svgAppIconPath.isEmpty() )
+    argumentList << settings.svgAppIconPath;
+  else
+    argumentList << "";
+  argumentList << summary; // summary
+  argumentList << body; // body
+  argumentList << QStringList();  // actions
+  argumentList << hints;  // hints
+  argumentList << -1; // timeout in ms "If -1, the notification's expiration time is dependent on the notification server's settings, and may vary for the type of notification."
+
+  QDBusMessage reply = iface.callWithArgumentList( QDBus::AutoDetect, QStringLiteral( "Notify" ), argumentList );
+  if ( reply.type() == QDBusMessage::ErrorMessage )
+  {
+    qDebug() << "D-Bus Error:" << reply.errorMessage();
+    return result;
+  }
+
+  result.successful = true;
+  result.messageId = reply.arguments().value( 0 );
+  return result;
+}

src/native/linux/qgslinuxnative.h

@@ -20,10 +20,22 @@
 
 #include "qgsnative.h"
 
+/**
+ * Native implementation for linux platforms.
+ *
+ * Implements the native platform interface for Linux based platforms. This is
+ * intended to expose desktop-agnostic implementations of the QgsNative methods,
+ * so that they work without issue across the wide range of Linux desktop environments
+ * (e.g. Gnome/KDE).
+ *
+ * Typically, this means implementing methods using DBUS calls to freedesktop standards.
+ */
 class NATIVE_EXPORT QgsLinuxNative : public QgsNative
 {
   public:
+    QgsNative::Capabilities capabilities() const override;
     void openFileExplorerAndSelectFile( const QString &path ) override;
+    NotificationResult showDesktopNotification( const QString &summary, const QString &body, const NotificationSettings &settings = NotificationSettings() ) override;
 };
 
 #endif // QGSLINUXNATIVE_H

src/native/qgsnative.cpp

@@ -21,6 +21,11 @@
 #include <QUrl>
 #include <QFileInfo>
 
+QgsNative::Capabilities QgsNative::capabilities() const
+{
+  return nullptr;
+}
+
 void QgsNative::initializeMainWindow( QWindow * )
 {
 
@@ -51,3 +56,10 @@ void QgsNative::hideApplicationProgress()
 {
 
 }
+
+QgsNative::NotificationResult QgsNative::showDesktopNotification( const QString &, const QString &, const NotificationSettings & )
+{
+  NotificationResult result;
+  result.successful = false;
+  return result;
+}

src/native/qgsnative.h

@@ -19,6 +19,8 @@
 #define QGSNATIVE_H
 
 #include "qgis_native.h"
+#include <QImage>
+#include <QVariant>
 
 class QString;
 class QWindow;
@@ -34,8 +36,20 @@ class NATIVE_EXPORT QgsNative
 {
   public:
 
+    //! Native interface capabilities
+    enum Capability
+    {
+      NativeDesktopNotifications = 1 << 1, //!< Native desktop notifications are supported. See showDesktopNotification().
+    };
+    Q_DECLARE_FLAGS( Capabilities, Capability )
+
     virtual ~QgsNative() = default;
 
+    /**
+     * Returns the native interface's capabilities.
+     */
+    virtual Capabilities capabilities() const;
+
     /**
      * Initializes the native interface, using the specified \a window.
      *
@@ -97,6 +111,59 @@ class NATIVE_EXPORT QgsNative
      */
     virtual void hideApplicationProgress();
 
+
+    /**
+     * Notification settings, for use with showDesktopNotification().
+     */
+    struct NotificationSettings
+    {
+      NotificationSettings() {}
+
+      //! Optional image to show in notification
+      QImage image;
+
+      //! Whether the notification should be transient (the meaning varies depending on platform)
+      bool transient = true;
+
+      //! Path to application icon in SVG format
+      QString svgAppIconPath;
+
+      //! Message ID, used to replace existing messages
+      QVariant messageId;
+    };
+
+    /**
+     * Result of sending a desktop notification, returned by showDesktopNotification().
+     */
+    struct NotificationResult
+    {
+      NotificationResult() {}
+
+      //! True if notification was successfully sent.
+      bool successful = false;
+
+      //! Unique notification message ID, used by some platforms to identify the notification
+      QVariant messageId;
+    };
+
+    /**
+     * Shows a native desktop notification.
+     *
+     * The \a summary argument specifies a short title for the notification, and the \a body argument
+     * specifies the complete notification message text.
+     *
+     * The \a settings argument allows fine-tuning of the notification, using a range of settings which
+     * may or may not be respected on all platforms. It is recommended to set as many of these properties
+     * as is applicable, and let the native implementation choose which to use based on the platform's
+     * capabilities.
+     *
+     * This method is only supported when the interface returns the NativeDesktopNotifications flag for capabilities().
+     *
+     * Returns true if notification was successfully sent.
+     */
+    virtual NotificationResult showDesktopNotification( const QString &summary, const QString &body, const NotificationSettings &settings = NotificationSettings() );
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS( QgsNative::Capabilities )
+
 #endif // QGSNATIVE_H