xcb: create fake screen when XRandR 1.2 and later unavailable

Keep the old behavior from 6.0 to 6.2.

Fixes: QTBUG-102637
Pick-to: 6.3
Change-Id: I2e596c7d5161a3dc7a8493358e272a481aee5308
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 25 insertions, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 6ce7184570..2d55524f6f 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -226,6 +226,7 @@ private:
                              xcb_randr_get_output_info_reply_t *outputInfo);
     void destroyScreen(QXcbScreen *screen);
     void initializeScreens(bool initialized);
+    void initializeScreensWithoutXRandR(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);
diff --git a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
index 149824bc92..aa0f2fef65 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
@@ -317,6 +317,10 @@ void QXcbConnection::initializeScreens(bool initialized)
             initializeScreensFromMonitor(&it, xcbScreenNumber, &primaryScreen, initialized);
         else if (isAtLeastXRandR12())
             initializeScreensFromOutput(&it, xcbScreenNumber, &primaryScreen);
+        else {
+            qWarning("There is no XRandR 1.2 and later version available. There will be only fake screen(s) to use.");
+            initializeScreensWithoutXRandR(&it, xcbScreenNumber, &primaryScreen);
+        }
 
         xcb_screen_next(&it);
         ++xcbScreenNumber;
@@ -349,6 +353,26 @@ void QXcbConnection::initializeScreens(bool initialized)
     }
 }
 
+void QXcbConnection::initializeScreensWithoutXRandR(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen **primaryScreen)
+{
+    // XRandR extension is missing, then create a fake/legacy screen.
+    xcb_screen_t *xcbScreen = it->data;
+    QXcbVirtualDesktop *virtualDesktop = new QXcbVirtualDesktop(this, xcbScreen, xcbScreenNumber);
+    m_virtualDesktops.append(virtualDesktop);
+    QList<QPlatformScreen *> siblings;
+
+    QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, XCB_NONE, nullptr);
+    qCDebug(lcQpaScreen) << "created fake screen" << screen;
+    m_screens << screen;
+
+    if (primaryScreenNumber() == xcbScreenNumber) {
+        *primaryScreen = screen;
+        (*primaryScreen)->setPrimary(true);
+    }
+    siblings << screen;
+    virtualDesktop->setScreens(std::move(siblings));
+}
+
 void QXcbConnection::initializeScreensFromOutput(xcb_screen_iterator_t *it, int xcbScreenNumber, QXcbScreen **primaryScreen)
 {
     // Each "screen" in xcb terminology is a virtual desktop,