[wayland] Forward EGLDisplay and EGLContext from Scene to Backend

AbstractBackend can forward the egl display and context, so that
it can be used from other parts.

abstract_backend.cpp

@@ -19,9 +19,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "abstract_backend.h"
 #include <config-kwin.h>
+#include "abstract_egl_backend.h"
 #include "composite.h"
 #include "cursor.h"
 #include "input.h"
+#include "scene_opengl.h"
 #include "wayland_server.h"
 #include "wayland_cursor_theme.h"
 // KWayland
@@ -303,4 +305,24 @@ void AbstractBackend::warpPointer(const QPointF &globalPos)
     Q_UNUSED(globalPos)
 }
 
+EGLDisplay AbstractBackend::sceneEglDisplay() const
+{
+    if (Compositor *c = Compositor::self()) {
+        if (SceneOpenGL *s = dynamic_cast<SceneOpenGL*>(c->scene())) {
+            return static_cast<AbstractEglBackend*>(s->backend())->eglDisplay();
+        }
+    }
+    return EGL_NO_DISPLAY;
+}
+
+EGLContext AbstractBackend::sceneEglContext() const
+{
+    if (Compositor *c = Compositor::self()) {
+        if (SceneOpenGL *s = dynamic_cast<SceneOpenGL*>(c->scene())) {
+            return static_cast<AbstractEglBackend*>(s->backend())->context();
+        }
+    }
+    return EGL_NO_CONTEXT;
+}
+
 }

abstract_backend.h

@@ -20,6 +20,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef KWIN_ABSTRACT_BACKEND_H
 #define KWIN_ABSTRACT_BACKEND_H
 #include <kwin_export.h>
+#include <epoxy/egl.h>
+#include <fixx11h.h>
 #include <QImage>
 #include <QObject>
 
@@ -44,6 +46,14 @@ public:
     virtual OpenGLBackend *createOpenGLBackend();
     virtual QPainterBackend *createQPainterBackend();
     virtual void warpPointer(const QPointF &globalPos);
+    /**
+     * The EGLDisplay used by the compositing scene.
+     **/
+    virtual EGLDisplay sceneEglDisplay() const;
+    /**
+     * The EGLContext used by the compositing scene.
+     **/
+    virtual EGLContext sceneEglContext() const;
 
     bool usesSoftwareCursor() const {
         return m_softWareCursor;

abstract_egl_backend.h

@@ -34,12 +34,12 @@ public:
     EGLDisplay eglDisplay() const {
         return m_display;
     }
-
-protected:
-    AbstractEglBackend();
     EGLContext context() const {
         return m_context;
     }
+
+protected:
+    AbstractEglBackend();
     EGLSurface surface() const {
         return m_surface;
     }