use a native event filter to notice the screen was swapped

Summary:
this replaces the approach with the expose event in
20b439a4f4 by directly monitoring the xcb screen change
notify native event

Test Plan:
attaching and detaching the external screen on a laptop
configured to deactivate the internal screen upon connection
same behavior as D3777

Reviewers: sebas, davidedmundson, #plasma

Reviewed By: davidedmundson, #plasma

Subscribers: pmuralidharan, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3822

CMakeLists.txt

@@ -82,7 +82,7 @@ set_package_properties(X11 PROPERTIES DESCRIPTION "X11 libraries"
                         PURPOSE "Required for building the X11 based workspace")
 
 if(X11_FOUND)
-  find_package(XCB MODULE REQUIRED COMPONENTS XCB)
+  find_package(XCB MODULE REQUIRED COMPONENTS XCB RANDR)
   set_package_properties(XCB PROPERTIES TYPE REQUIRED)
   if(NOT X11_SM_FOUND)
     message(FATAL_ERROR "\nThe X11 Session Management (SM) development package could not be found.\nPlease install libSM.\n")

shell/CMakeLists.txt

@@ -100,7 +100,7 @@ target_include_directories(plasmashell PRIVATE "${CMAKE_BINARY_DIR}")
 target_compile_definitions(plasmashell PRIVATE -DPROJECT_VERSION="${PROJECT_VERSION}")
 
 if(HAVE_X11)
-  target_link_libraries(plasmashell ${X11_LIBRARIES} XCB::XCB )
+  target_link_libraries(plasmashell ${X11_LIBRARIES} ${XCB_LIBRARIES} )
   target_link_libraries(plasmashell Qt5::X11Extras)
 endif()
 

shell/autotests/CMakeLists.txt

@@ -10,6 +10,10 @@ MACRO(PLASMASHELL_UNIT_TESTS)
                             Qt5::Gui
                             KF5::Service
                                      )
+               if(HAVE_X11)
+                  target_link_libraries(${_testname} ${X11_LIBRARIES} ${XCB_LIBRARIES} )
+                  target_link_libraries(${_testname} Qt5::X11Extras)
+               endif()
                if(QT_QTOPENGL_FOUND)
                    target_link_libraries(${_testname} Qt5::OpenGL)
                endif()

shell/desktopview.cpp

@@ -85,7 +85,6 @@ void DesktopView::setScreenToFollow(QScreen *screen)
         return;
     }
 
-    m_screenName = screen->name();
     m_screenToFollow = screen;
     setScreen(screen);
     adaptToScreen();
@@ -199,17 +198,7 @@ DesktopView::SessionType DesktopView::sessionType() const
 
 bool DesktopView::event(QEvent *e)
 {
-    //NOTE: we need this heuristic for the case when there is an
-    //internal laptop screen that gets disabled upon connection of an external one. the only QCreen * pointer gets recycled and there is no dedicated signal to discover this at all
-    //after being moved, the view will get an expose event, so we can check there if the screen has been renamed
-    //see https://bugs.kde.org/show_bug.cgi?id=373880
-    //https://bugreports.qt.io/browse/QTBUG-57785
-    if (e->type() == QEvent::Expose) {
-        if (m_screenToFollow && m_screenToFollow->name() != m_screenName) {
-            m_screenName = m_screenToFollow->name();
-            emit screenRenamed();
-        }
-    } else if (e->type() == QEvent::KeyRelease) {
+    if (e->type() == QEvent::KeyRelease) {
         QKeyEvent *ke = static_cast<QKeyEvent *>(e);
         if (KWindowSystem::showingDesktop() && ke->key() == Qt::Key_Escape) {
             ShellCorona *c = qobject_cast<ShellCorona *>(corona());

shell/desktopview.h

@@ -88,14 +88,12 @@ private Q_SLOTS:
 Q_SIGNALS:
     void stayBehindChanged();
     void windowTypeChanged();
-    void screenRenamed();
 
 private:
     void coronaPackageChanged(const KPackage::Package &package);
     void ensureWindowType();
     void setupWaylandIntegration();
 
-    QString m_screenName;
     QPointer<PlasmaQuick::ConfigView> m_configView;
     QPointer<QScreen> m_oldScreen;
     QPointer<QScreen> m_screenToFollow;

shell/screenpool.cpp

@@ -18,14 +18,24 @@
  */
 
 #include "screenpool.h"
+#include <config-plasma.h>
 
 #include <QGuiApplication>
 #include <QScreen>
 
+#if HAVE_X11
+#include <QtX11Extras/QX11Info>
+#include <xcb/xcb.h>
+#include <xcb/randr.h>
+#include <xcb/xcb_event.h>
+#endif
+
 ScreenPool::ScreenPool(KSharedConfig::Ptr config, QObject *parent)
     : QObject(parent),
       m_configGroup(KConfigGroup(config, QStringLiteral("ScreenConnectors")))
 {
+    qApp->installNativeEventFilter(this);
+
     m_configSaveTimer.setSingleShot(true);
     connect(&m_configSaveTimer, &QTimer::timeout, this, [this](){
         m_configGroup.sync();
@@ -159,5 +169,38 @@ QList <int> ScreenPool::knownIds() const
     return m_connectorForId.keys();
 }
 
+bool ScreenPool::nativeEventFilter(const QByteArray& eventType, void* message, long int* result)
+{
+    Q_UNUSED(result);
+#if HAVE_X11
+    // a particular edge case: when we switch the only enabled screen
+    // we don't have any signal about it, the primary screen changes but we have the same old QScreen* getting recycled
+    // see https://bugs.kde.org/show_bug.cgi?id=373880
+    // if this slot will be invoked many times, their//second time on will do nothing as name and primaryconnector will be the same by then
+    if (eventType != "xcb_generic_event_t") {
+        return false;
+    }
+    
+    xcb_generic_event_t *ev = static_cast<xcb_generic_event_t *>(message);
+
+    const auto responseType = XCB_EVENT_RESPONSE_TYPE(ev);
+
+    const xcb_query_extension_reply_t* reply = xcb_get_extension_data(QX11Info::connection(), &xcb_randr_id);
+
+    if (responseType == reply->first_event + XCB_RANDR_SCREEN_CHANGE_NOTIFY) {
+        if (qGuiApp->primaryScreen()->name() != primaryConnector()) {
+            //new screen?
+            if (id(qGuiApp->primaryScreen()->name()) < 0) {
+                insertScreenMapping(firstAvailableId(), qGuiApp->primaryScreen()->name());
+            }
+            //switch the primary screen in the pool
+            setPrimaryConnector(qGuiApp->primaryScreen()->name());
+        }
+    }
+#endif
+    return false;
+}
+
+
 #include "moc_screenpool.cpp"
 

shell/screenpool.h

@@ -24,11 +24,13 @@
 #include <QHash>
 #include <QString>
 #include <QTimer>
+#include <QAbstractNativeEventFilter>
 
 #include <KConfigGroup>
 #include <KSharedConfig>
 
-class ScreenPool : public QObject {
+class ScreenPool : public QObject, public QAbstractNativeEventFilter
+{
     Q_OBJECT
 
 public:
@@ -50,6 +52,9 @@ public:
     //all ids that are known, included screens not enabled at the moment
     QList <int> knownIds() const;
 
+protected:
+    bool nativeEventFilter(const QByteArray & eventType, void * message, long * result) Q_DECL_OVERRIDE;
+
 private:
     void save();
 

shell/shellcorona.cpp

@@ -80,6 +80,7 @@
 #if HAVE_X11
 #include <NETWM>
 #include <QtX11Extras/QX11Info>
+#include <xcb/xcb.h>
 #endif
 
 
@@ -1149,20 +1150,6 @@ void ShellCorona::addOutput(QScreen* screen)
 
     DesktopView *view = new DesktopView(this, screen);
     connect(view, &QQuickWindow::sceneGraphError, this, &ShellCorona::showOpenGLNotCompatibleWarning);
-    // a particular edge case: when we switch the only enabled screen
-    // we don't have any signal about it, the primary screen changes but we have the same old QScreen* getting recycled
-    // see https://bugs.kde.org/show_bug.cgi?id=373880
-    // if this slot will be invoked many times, their//second time on will do nothing as name and primaryconnector will be the same by then
-    connect(view, &DesktopView::screenRenamed, this, [=](){
-        if (qGuiApp->primaryScreen()->name() != m_screenPool->primaryConnector()) {
-            //new screen?
-            if (m_screenPool->id(qGuiApp->primaryScreen()->name()) < 0) {
-                m_screenPool->insertScreenMapping(m_screenPool->firstAvailableId(), qGuiApp->primaryScreen()->name());
-            }
-            //switch the primary screen in the pool
-            m_screenPool->setPrimaryConnector(qGuiApp->primaryScreen()->name());
-        }
-    });
 
     Plasma::Containment *containment = createContainmentForActivity(m_activityController->currentActivity(), insertPosition);
     Q_ASSERT(containment);

shell/shellcorona.h

@@ -242,6 +242,7 @@ private:
     QSet<QScreen*> m_redundantOutputs;
     QList<KDeclarative::QmlObject *> m_alternativesObjects;
     KDeclarative::QmlObject *m_interactiveConsole;
+    int m_eventBase;
 
     QTimer m_waitingPanelsTimer;
     QTimer m_appConfigSyncTimer;