xcb: only set primary for monitor on primary X screen

It's possible to have multiple X screens, and a primary monitor on
each X screen. We should only use one on primary X screen as
primary QScreen.

The reference of QXcbScreen pointer should be used correctly.

Fixes: QTBUG-102758
Pick-to: 6.3
Change-Id: I1eafd509c8c109606967a4abe9ad7e9d8c0dd464
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

3 files changed, 36 insertions, 22 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 24e2d4a121..6ce7184570 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -226,14 +226,14 @@ private:
                              xcb_randr_get_output_info_reply_t *outputInfo);
     void destroyScreen(QXcbScreen *screen);
     void initializeScreens(bool initialized);
-    void initializeScreensFromOutput(xcb_screen_iterator_t *it, int screenNumber, QXcbScreen *primaryScreen);
+    void initializeScreensFromOutput(xcb_screen_iterator_t *it, int screenNumber, QXcbScreen **primaryScreen);
 
     void updateScreen_monitor(QXcbScreen *screen, xcb_randr_monitor_info_t *monitorInfo, xcb_timestamp_t timestamp = XCB_NONE);
     QXcbScreen *createScreen_monitor(QXcbVirtualDesktop *virtualDesktop,
                                      xcb_randr_monitor_info_t *monitorInfo, xcb_timestamp_t timestamp = XCB_NONE);
     QXcbVirtualDesktop* virtualDesktopForNumber(int n) const;
     QXcbScreen* findScreenForMonitorInfo(const QList<QPlatformScreen *> &screens, xcb_randr_monitor_info_t *monitorInfo);
-    void initializeScreensFromMonitor(xcb_screen_iterator_t *it, int screenNumber, QXcbScreen *primaryScreen, bool initialized);
+    void initializeScreensFromMonitor(xcb_screen_iterator_t *it, int screenNumber, QXcbScreen **primaryScreen, bool initialized);
 
     bool compressEvent(xcb_generic_event_t *event) const;
     inline bool timeGreaterThan(xcb_timestamp_t a, xcb_timestamp_t b) const
diff --git a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
index 5aab3a04f2..149824bc92 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
@@ -309,11 +309,14 @@ void QXcbConnection::initializeScreens(bool initialized)
     xcb_screen_iterator_t it = xcb_setup_roots_iterator(setup());
     int xcbScreenNumber = 0;    // screen number in the xcb sense
     QXcbScreen *primaryScreen = nullptr;
+    if (isAtLeastXRandR15() && initialized)
+        m_screens.clear();
+
     while (it.rem) {
         if (isAtLeastXRandR15())
-            initializeScreensFromMonitor(&it, xcbScreenNumber, primaryScreen, initialized);
+            initializeScreensFromMonitor(&it, xcbScreenNumber, &primaryScreen, initialized);
         else if (isAtLeastXRandR12())
-            initializeScreensFromOutput(&it, xcbScreenNumber, primaryScreen);
+            initializeScreensFromOutput(&it, xcbScreenNumber, &primaryScreen);
 
         xcb_screen_next(&it);
         ++xcbScreenNumber;
@@ -346,7 +349,7 @@ void QXcbConnection::initializeScreens(bool initialized)
     }
 }
 
-void QXcbConnection::initializeScreensFromOutput(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen *primaryScreen)
+void QXcbConnection::initializeScreensFromOutput(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen **primaryScreen)
 {
     // Each "screen" in xcb terminology is a virtual desktop,
     // potentially a collection of separate juxtaposed monitors.
@@ -420,11 +423,11 @@ void QXcbConnection::initializeScreensFromOutput(xcb_screen_iterator_t *it, int
                         // always available if primary->output is XCB_NONE
                         // or currently disconnected output.
                         if (primaryScreenNumber() == xcbScreenNumber) {
-                            if (!primaryScreen || (primary && outputs[i] == primary->output)) {
-                                if (primaryScreen)
-                                    primaryScreen->setPrimary(false);
-                                primaryScreen = screen;
-                                primaryScreen->setPrimary(true);
+                            if (!(*primaryScreen) || (primary && outputs[i] == primary->output)) {
+                                if (*primaryScreen)
+                                    (*primaryScreen)->setPrimary(false);
+                                *primaryScreen = screen;
+                                (*primaryScreen)->setPrimary(true);
                                 siblings.prepend(siblings.takeLast());
                             }
                         }
@@ -440,15 +443,15 @@ void QXcbConnection::initializeScreensFromOutput(xcb_screen_iterator_t *it, int
         qCDebug(lcQpaScreen) << "created fake screen" << screen;
         m_screens << screen;
         if (primaryScreenNumber() == xcbScreenNumber) {
-            primaryScreen = screen;
-            primaryScreen->setPrimary(true);
+            *primaryScreen = screen;
+            (*primaryScreen)->setPrimary(true);
         }
         siblings << screen;
     }
     virtualDesktop->setScreens(std::move(siblings));
 }
 
-void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen *primaryScreen, bool initialized)
+void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen **primaryScreen, bool initialized)
 {
     // Each "screen" in xcb terminology is a virtual desktop,
     // potentially a collection of separate juxtaposed monitors.
@@ -463,8 +466,6 @@ void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int
         m_virtualDesktops.append(virtualDesktop);
     }
     QList<QPlatformScreen*> old = virtualDesktop->m_screens;
-    if (initialized)
-        m_screens.clear();
 
     QList<QPlatformScreen *> siblings;
 
@@ -482,21 +483,30 @@ void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int
         QXcbScreen *screen = nullptr;
         if (!initialized) {
             screen = new QXcbScreen(this, virtualDesktop, monitor_info, monitors_r->timestamp);
-            m_screens << screen;
         } else {
-            screen = findScreenForMonitorInfo(virtualDesktop->m_screens, monitor_info);
+            screen = findScreenForMonitorInfo(old, monitor_info);
             if (!screen) {
                 screen = createScreen_monitor(virtualDesktop, monitor_info, monitors_r->timestamp);
                 QHighDpiScaling::updateHighDpiScaling();
             } else {
-                m_screens << screen;
                 updateScreen_monitor(screen, monitor_info, monitors_r->timestamp);
                 old.removeAll(screen);
             }
         }
-
+        m_screens << screen;
         siblings << screen;
 
+        // similar logic with QXcbConnection::initializeScreensFromOutput()
+        if (primaryScreenNumber() == xcbScreenNumber) {
+            if (!(*primaryScreen) || monitor_info->primary) {
+                if (*primaryScreen)
+                    (*primaryScreen)->setPrimary(false);
+                *primaryScreen = screen;
+                (*primaryScreen)->setPrimary(true);
+                siblings.prepend(siblings.takeLast());
+            }
+        }
+
         xcb_randr_monitor_info_next(&monitor_iter);
     }
     free(monitors_r);
@@ -518,9 +528,10 @@ void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int
         }
 
         if (primaryScreenNumber() == xcbScreenNumber) {
-            primaryScreen = screen;
-            primaryScreen->setPrimary(true);
+            *primaryScreen = screen;
+            (*primaryScreen)->setPrimary(true);
         }
+
         siblings << screen;
         m_screens << screen;
     }
diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index f5ba55897c..bb33f393ec 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -678,7 +678,10 @@ void QXcbScreen::setMonitor(xcb_randr_monitor_info_t *monitorInfo, xcb_timestamp
         m_sizeMillimeters = virtualDesktop()->physicalSize();
 
     m_outputName = getName(monitorInfo);
-    m_primary = monitorInfo->primary;
+    if (connection()->primaryScreenNumber() == virtualDesktop()->number() && monitorInfo->primary)
+        m_primary = true;
+    else
+        m_primary = false;
 
     m_cursor = new QXcbCursor(connection(), this);