[wayland] Allow the AbstractBackend subclasses to manage OutputInterfaces

This gives the backend more control without needing to provide all
information in Screens.

abstract_backend.h

@@ -58,6 +58,10 @@ public:
     }
     void markCursorAsRendered();
 
+    bool handlesOutputs() const {
+        return m_handlesOutputs;
+    }
+
 Q_SIGNALS:
     void cursorChanged();
 
@@ -66,6 +70,9 @@ protected:
     void setSoftWareCursor(bool set);
     void updateCursorFromServer();
     void updateCursorImage(Qt::CursorShape shape);
+    void handleOutputs() {
+        m_handlesOutputs = true;
+    }
 
 private Q_SLOTS:
     void installThemeCursor(quint32 id, const QPoint &hotspot);
@@ -79,6 +86,7 @@ private:
         QPoint lastRenderedPosition;
     } m_cursor;
     Wayland::WaylandCursorTheme *m_cursorTheme = nullptr;
+    bool m_handlesOutputs = false;
 };
 
 }

wayland_server.cpp

@@ -18,6 +18,7 @@ You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "wayland_server.h"
+#include "abstract_backend.h"
 #include "screens.h"
 #include "toplevel.h"
 #include "workspace.h"
@@ -84,6 +85,9 @@ void WaylandServer::init(const QByteArray &socketName)
 
 void WaylandServer::initOutputs()
 {
+    if (m_backend && m_backend->handlesOutputs()) {
+        return;
+    }
     Screens *s = screens();
     Q_ASSERT(s);
     for (int i = 0; i < s->count(); ++i) {