[wayland] Create Screens through the AbstractBackend

The AbstractBackend provides a virtual method to create the Screens.
A concrete backend can implement this method to create the backend
specific Screens instance.

This removes the casting logic from Screens::create.

abstract_backend.cpp

@@ -43,4 +43,10 @@ void AbstractBackend::installCursorImage(Qt::CursorShape shape)
     Q_UNUSED(shape)
 }
 
+Screens *AbstractBackend::createScreens(QObject *parent)
+{
+    Q_UNUSED(parent)
+    return nullptr;
+}
+
 }

abstract_backend.h

@@ -25,6 +25,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
+class Screens;
+
 class KWIN_EXPORT AbstractBackend : public QObject
 {
     Q_OBJECT
@@ -33,6 +35,7 @@ public:
 
     virtual void installCursorFromServer();
     virtual void installCursorImage(Qt::CursorShape shape);
+    virtual Screens *createScreens(QObject *parent = nullptr);
 
 protected:
     explicit AbstractBackend(QObject *parent = nullptr);

screens.cpp

@@ -25,11 +25,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <config-kwin.h>
 #include "screens_xrandr.h"
 #if HAVE_WAYLAND
-#include "screens_wayland.h"
-#include "wayland_backend.h"
+#include "abstract_backend.h"
 #include "wayland_server.h"
-#include "x11windowed_backend.h"
-#include "screens_x11windowed.h"
 #endif
 #ifdef KWIN_UNIT_TEST
 #include <mock_screens.h>
@@ -47,11 +44,7 @@ Screens *Screens::create(QObject *parent)
 #else
 #if HAVE_WAYLAND
     if (kwinApp()->shouldUseWaylandForCompositing()) {
-        if (X11WindowedBackend *b = dynamic_cast<X11WindowedBackend*>(waylandServer()->backend())) {
-            s_self = new X11WindowedScreens(b, parent);
-        } else if (Wayland::WaylandBackend *b = dynamic_cast<Wayland::WaylandBackend*>(waylandServer()->backend())) {
-            s_self = new WaylandScreens(b, parent);
-        }
+        s_self = waylandServer()->backend()->createScreens(parent);
     }
 #endif
     if (kwinApp()->operationMode() == Application::OperationModeX11) {

wayland_backend.cpp

@@ -23,6 +23,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "cursor.h"
 #include "input.h"
 #include "main.h"
+#include "screens_wayland.h"
 #include "utils.h"
 #include "wayland_server.h"
 #include <KWayland/Client/buffer.h>
@@ -639,6 +640,11 @@ void WaylandBackend::connectNotify(const QMetaMethod &signal)
     }
 }
 
+Screens *WaylandBackend::createScreens(QObject *parent)
+{
+    return new WaylandScreens(this, parent);
+}
+
 }
 
 } // KWin

wayland_backend.h

@@ -169,6 +169,8 @@ public:
     void installCursorImage(Qt::CursorShape shape) override;
     void installCursorFromServer() override;
 
+    Screens *createScreens(QObject *parent = nullptr) override;
+
 protected:
     void connectNotify(const QMetaMethod &signal) override;
 

x11windowed_backend.cpp

@@ -20,6 +20,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "x11windowed_backend.h"
 #include "composite.h"
 #include "input.h"
+#include "screens_x11windowed.h"
 #include "utils.h"
 #include "wayland_server.h"
 #include "xcbutils.h"
@@ -293,4 +294,9 @@ xcb_window_t X11WindowedBackend::rootWindow() const
     return m_screen->root;
 }
 
+Screens *X11WindowedBackend::createScreens(QObject *parent)
+{
+    return new X11WindowedScreens(this, parent);
+}
+
 }

x11windowed_backend.h

@@ -66,6 +66,8 @@ public:
 
     void installCursorFromServer() override;
 
+    Screens *createScreens(QObject *parent = nullptr) override;
+
 Q_SIGNALS:
     void sizeChanged();