[wayland] Create xcb_connection through XLib in windowed mode

Adds optional dependency to X11_XCB and gets used in X11WindowedBackend
to create an XLib Display if dependency is present.

This allows to create an EGL backend for the X11WindowedBackend.

CMakeLists.txt

@@ -191,6 +191,11 @@ if (XCB_VERSION VERSION_LESS "1.10")
 endif()
 add_feature_info("XCB-SYNC" HAVE_XCB_SYNC "XCB Sync version >= 1.10 required for synced window resizing")
 
+find_package(X11_XCB)
+set_package_properties(X11_XCB PROPERTIES
+                       PURPOSE "Required for OpenGL support in X11 windowed backend of kwin_wayland"
+                       TYPE OPTIONAL)
+
 feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
 
 ########### configure tests ###############
@@ -275,6 +280,8 @@ else()
     set(HAVE_XCB_CURSOR FALSE)
 endif()
 
+set(HAVE_X11_XCB ${X11_XCB_FOUND})
+
 include(CheckIncludeFiles)
 check_include_files(unistd.h HAVE_UNISTD_H)
 check_include_files(malloc.h HAVE_MALLOC_H)
@@ -510,6 +517,10 @@ set(kwin_WAYLAND_EGL_LIBS
     Wayland::Egl
 )
 
+if(X11_XCB_FOUND)
+    set(kwin_WAYLAND_LIBS ${kwin_WAYLAND_LIBS} X11::XCB)
+endif()
+
 if(KWIN_BUILD_ACTIVITIES)
     set(kwin_KDE_LIBS ${kwin_KDE_LIBS} KF5::Activities)
 endif()

config-kwin.h.cmake

@@ -15,6 +15,7 @@
 #cmakedefine01 HAVE_INPUT
 #cmakedefine01 HAVE_XCB_CURSOR
 #cmakedefine01 HAVE_XCB_SYNC
+#cmakedefine01 HAVE_X11_XCB
 
 /* Define to 1 if you have the <unistd.h> header file. */
 #cmakedefine HAVE_UNISTD_H 1

x11windowed_backend.cpp

@@ -34,6 +34,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KWayland/Server/surface_interface.h>
 // system
 #include <linux/input.h>
+#if HAVE_X11_XCB
+#include <X11/Xlib-xcb.h>
+#endif
 
 namespace KWin
 {
@@ -52,10 +55,23 @@ X11WindowedBackend::X11WindowedBackend(const QString &display, const QSize &size
     , m_size(size)
 {
     int screen = 0;
-    auto c = xcb_connect(display.toUtf8().constData(), &screen);
+    xcb_connection_t *c = nullptr;
-    if (!xcb_connection_has_error(c)) {
+#if HAVE_X11_XCB
+    Display *xDisplay = XOpenDisplay(display.toUtf8().constData());
+    if (xDisplay) {
+        c = XGetXCBConnection(xDisplay);
+        XSetEventQueueOwner(xDisplay, XCBOwnsEventQueue);
+        screen = XDefaultScreen(xDisplay);
+    }
+#else
+    c = xcb_connect(display.toUtf8().constData(), &screen);
+#endif
+    if (c && !xcb_connection_has_error(c)) {
         m_connection = c;
         m_screenNumber = screen;
+#if HAVE_X11_XCB
+        m_display = xDisplay;
+#endif
         for (xcb_screen_iterator_t it = xcb_setup_roots_iterator(xcb_get_setup(m_connection));
             it.rem;
             --screen, xcb_screen_next(&it)) {

x11windowed_backend.h

@@ -27,6 +27,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <xcb/xcb.h>
 
+struct _XDisplay;
+typedef struct _XDisplay Display;
+
 namespace KWin
 {
 
@@ -46,6 +49,9 @@ public:
     xcb_window_t window() const {
         return m_window;
     }
+    Display *display() const {
+        return m_display;
+    }
 
     bool isValid() const {
         return m_connection != nullptr && m_window != XCB_WINDOW_NONE;
@@ -81,6 +87,7 @@ private:
     xcb_atom_t m_protocols = XCB_ATOM_NONE;
     xcb_atom_t m_deleteWindowProtocol = XCB_ATOM_NONE;
     xcb_cursor_t m_cursor = XCB_CURSOR_NONE;
+    Display *m_display = nullptr;
     static X11WindowedBackend *s_self;
 };