scene: Use standard wl_surface item for Xwayland surfaces

Besides unifying the code, it fixes some visual glitches caused by the
opaque region getting out of sync.

Xwayland MR: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1698

src/scene/surfaceitem_wayland.cpp

@@ -12,11 +12,6 @@
 #include "wayland/linuxdmabufv1clientbuffer.h"
 #include "wayland/subcompositor.h"
 #include "wayland/surface.h"
-#include "window.h"
-
-#if KWIN_BUILD_X11
-#include "x11window.h"
-#endif
 
 namespace KWin
 {
@@ -247,22 +242,6 @@ bool SurfacePixmapWayland::isValid() const
     return m_bufferRef;
 }
 
-#if KWIN_BUILD_X11
-SurfaceItemXwayland::SurfaceItemXwayland(X11Window *window, Item *parent)
-    : SurfaceItemWayland(window->surface(), parent)
-    , m_window(window)
-{
-}
-
-QRegion SurfaceItemXwayland::opaque() const
-{
-    if (!m_window->hasAlpha()) {
-        return rect().toRect();
-    } else {
-        return m_window->opaqueRegion() & rect().toRect();
-    }
-}
-#endif
 } // namespace KWin
 
 #include "moc_surfaceitem_wayland.cpp"

src/scene/surfaceitem_wayland.h

@@ -16,7 +16,6 @@ namespace KWin
 class GraphicsBuffer;
 class SubSurfaceInterface;
 class SurfaceInterface;
-class X11Window;
 
 /**
  * The SurfaceItemWayland class represents a Wayland surface in the scene.
@@ -83,22 +82,4 @@ private:
     SurfaceItemWayland *m_item;
 };
 
-#if KWIN_BUILD_X11
-/**
- * The SurfaceItemXwayland class represents an Xwayland surface in the scene.
- */
-class KWIN_EXPORT SurfaceItemXwayland : public SurfaceItemWayland
-{
-    Q_OBJECT
-
-public:
-    explicit SurfaceItemXwayland(X11Window *window, Item *parent = nullptr);
-
-    QRegion opaque() const override;
-
-private:
-    X11Window *m_window;
-};
-#endif
-
 } // namespace KWin

src/scene/windowitem.cpp

@@ -323,7 +323,7 @@ void WindowItemX11::initialize()
         if (!window()->surface()) {
             updateSurfaceItem(nullptr);
         } else {
-            updateSurfaceItem(std::make_unique<SurfaceItemXwayland>(static_cast<X11Window *>(window()), this));
+            updateSurfaceItem(std::make_unique<SurfaceItemWayland>(window()->surface(), this));
         }
         break;
     case Application::OperationModeWaylandOnly: