Let QXcbGlxWindow::createVisual fallback to QXcbWindow::createVisual

When flatpak refused to install org.freedesktop.Platform.GL.default for
me, I got into a situation without GL drivers and Qt applications
stopped getting transparency windows.

They fallback to use root_visual and it doesn't provide sufaces with
alpha, I tried to add fallback to QXcbWindow::createVisual just like
QXcbEglWindow::createVisual does and voila, they got transparency.

Pick-to: 6.3 6.2 5.15
Change-Id: I9f401643b3ef231048c6e9e250121c96514101f5
Reviewed-by: Liang Qi <liang.qi@qt.io>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
index c021388c5b..45fbe75333 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
@@ -58,7 +58,7 @@ const xcb_visualtype_t *QXcbGlxWindow::createVisual()
 {
     QXcbScreen *scr = xcbScreen();
     if (!scr)
-        return nullptr;
+        return QXcbWindow::createVisual();
 
     qCDebug(lcQpaGl) << "Requested format before FBConfig/Visual selection:" << m_format;
 
@@ -71,10 +71,13 @@ const xcb_visualtype_t *QXcbGlxWindow::createVisual()
             flags |= QGLX_SUPPORTS_SRGB;
     }
 
+    const auto formatBackup = m_format;
     XVisualInfo *visualInfo = qglx_findVisualInfo(dpy, scr->screenNumber(), &m_format, GLX_WINDOW_BIT, flags);
     if (!visualInfo) {
-        qWarning() << "No XVisualInfo for format" << m_format;
-        return nullptr;
+        qCDebug(lcQpaGl) << "No XVisualInfo for format" << m_format;
+        // restore initial format before requesting it again
+        m_format = formatBackup;
+        return QXcbWindow::createVisual();
     }
     const xcb_visualtype_t *xcb_visualtype = scr->visualForId(visualInfo->visualid);
     XFree(visualInfo);