[wayland] Create OpenGLBackend through the AbstractBackend

Replaces casting logic in the SceneOpenGL. Now the create is delegated
to the backend allowing also to move the ifdef logic to where it belongs.

abstract_backend.cpp

@@ -49,4 +49,9 @@ Screens *AbstractBackend::createScreens(QObject *parent)
     return nullptr;
 }
 
+OpenGLBackend *AbstractBackend::createOpenGLBackend()
+{
+    return nullptr;
+}
+
 }

abstract_backend.h

@@ -25,6 +25,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
+class OpenGLBackend;
 class Screens;
 
 class KWIN_EXPORT AbstractBackend : public QObject
@@ -36,6 +37,7 @@ public:
     virtual void installCursorFromServer();
     virtual void installCursorImage(Qt::CursorShape shape);
     virtual Screens *createScreens(QObject *parent = nullptr);
+    virtual OpenGLBackend *createOpenGLBackend();
 
 protected:
     explicit AbstractBackend(QObject *parent = nullptr);

scene_opengl.cpp

@@ -29,22 +29,16 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "scene_opengl.h"
 #ifdef KWIN_HAVE_EGL
 #include "eglonxbackend.h"
-// for Wayland
-#if HAVE_WAYLAND
-#include "wayland_server.h"
-#if HAVE_WAYLAND_EGL
-#include "egl_wayland_backend.h"
-#include "wayland_backend.h"
-#endif // HAVE_WAYLAND_EGL
-#if HAVE_X11_XCB
-#include "x11windowed_backend.h"
-#endif // HAVE_X11_XCB
-#endif // HAVE_WAYLAND
 #endif // KWIN_HAVE_EGL
 #ifndef KWIN_HAVE_OPENGLES
 #include "glxbackend.h"
 #endif // KWIN_HAVE_OPENGLES
 
+#if HAVE_WAYLAND
+#include "abstract_backend.h"
+#include "wayland_server.h"
+#endif // HAVE_WAYLAND
+
 #include <kwinglcolorcorrection.h>
 #include <kwinglplatform.h>
 
@@ -503,18 +497,7 @@ SceneOpenGL *SceneOpenGL::createScene(QObject *parent)
 #ifdef KWIN_HAVE_EGL
 #if HAVE_WAYLAND
         if (kwinApp()->shouldUseWaylandForCompositing()) {
-#if HAVE_WAYLAND_EGL
-            if (Wayland::WaylandBackend *b = dynamic_cast<Wayland::WaylandBackend*>(waylandServer()->backend())) {
-                backend = new EglWaylandBackend(b);
-            }
-#endif // HAVE_WAYLAND_EGL
-#if HAVE_X11_XCB
-            if (!backend) {
-                if (X11WindowedBackend *b = dynamic_cast<X11WindowedBackend*>(waylandServer()->backend())) {
-                    backend = new EglOnXBackend(b);
-                }
-            }
-#endif // HAVE_X11_XCB
+            backend = waylandServer()->backend()->createOpenGLBackend();
         } else
 #endif // HAVE_WAYLAND
         {

wayland_backend.cpp

@@ -26,6 +26,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "screens_wayland.h"
 #include "utils.h"
 #include "wayland_server.h"
+#if HAVE_WAYLAND_EGL
+#include "egl_wayland_backend.h"
+#endif
 #include <KWayland/Client/buffer.h>
 #include <KWayland/Client/compositor.h>
 #include <KWayland/Client/connection_thread.h>
@@ -645,6 +648,15 @@ Screens *WaylandBackend::createScreens(QObject *parent)
     return new WaylandScreens(this, parent);
 }
 
+OpenGLBackend *WaylandBackend::createOpenGLBackend()
+{
+#if HAVE_WAYLAND_EGL
+    return new EglWaylandBackend(this);
+#else
+    return nullptr;
+#endif
+}
+
 }
 
 } // KWin

wayland_backend.h

@@ -170,6 +170,7 @@ public:
     void installCursorFromServer() override;
 
     Screens *createScreens(QObject *parent = nullptr) override;
+    OpenGLBackend *createOpenGLBackend() override;
 
 protected:
     void connectNotify(const QMetaMethod &signal) override;

x11windowed_backend.cpp

@@ -24,6 +24,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "utils.h"
 #include "wayland_server.h"
 #include "xcbutils.h"
+#ifdef KWIN_HAVE_EGL
+#if HAVE_X11_XCB
+#include "eglonxbackend.h"
+#endif
+#endif
 #include <kwinxrenderutils.h>
 #include <QAbstractEventDispatcher>
 #include <QCoreApplication>
@@ -299,4 +304,14 @@ Screens *X11WindowedBackend::createScreens(QObject *parent)
     return new X11WindowedScreens(this, parent);
 }
 
+OpenGLBackend *X11WindowedBackend::createOpenGLBackend()
+{
+#ifdef KWIN_HAVE_EGL
+#if HAVE_X11_XCB
+    return  new EglOnXBackend(this);
+#endif
+#endif
+    return nullptr;
+}
+
 }

x11windowed_backend.h

@@ -67,6 +67,7 @@ public:
     void installCursorFromServer() override;
 
     Screens *createScreens(QObject *parent = nullptr) override;
+    OpenGLBackend *createOpenGLBackend() override;
 
 Q_SIGNALS:
     void sizeChanged();