xwayland: Make DataBridge a native event filter

With the DataBridge being a native event filter, we can further separate
DataBridge-specific and generic Xwayland bits. In particular, we no
longer have to call DataBridge::filterEvent() from the dispatchEvents()
method, whose main purpose is to dispatch X11 events to kwin.

xwl/databridge.cpp

@@ -81,15 +81,14 @@ void DataBridge::init()
     m_clipboard = new Clipboard(atoms->clipboard, this);
     m_dnd = new Dnd(atoms->xdnd_selection, this);
     waylandServer()->dispatch();
+    kwinApp()->installNativeEventFilter(this);
 }
 
-bool DataBridge::filterEvent(xcb_generic_event_t *event)
+bool DataBridge::nativeEventFilter(const QByteArray &eventType, void *message, long int *)
 {
-    if (m_clipboard && m_clipboard->filterEvent(event)) {
+    if (eventType == "xcb_generic_event_t") {
-        return true;
+        xcb_generic_event_t *event = static_cast<xcb_generic_event_t *>(message);
-    }
+        return m_clipboard->filterEvent(event) || m_dnd->filterEvent(event);
-    if (m_dnd && m_dnd->filterEvent(event)) {
-        return true;
     }
     return false;
 }

xwl/databridge.h

@@ -9,6 +9,7 @@
 #ifndef KWIN_XWL_DATABRIDGE
 #define KWIN_XWL_DATABRIDGE
 
+#include <QAbstractNativeEventFilter>
 #include <QObject>
 #include <QPoint>
 
@@ -42,7 +43,7 @@ enum class DragEventReply;
  *
  * Exists only once per Xwayland session.
  */
-class DataBridge : public QObject
+class DataBridge : public QObject, public QAbstractNativeEventFilter
 {
     Q_OBJECT
 
@@ -52,7 +53,6 @@ public:
     explicit DataBridge(QObject *parent = nullptr);
     ~DataBridge() override;
 
-    bool filterEvent(xcb_generic_event_t *event);
     DragEventReply dragMoveFilter(Toplevel *target, const QPoint &pos);
 
     KWayland::Client::DataDevice *dataDevice() const
@@ -68,6 +68,8 @@ public:
         return m_dnd;
     }
 
+    bool nativeEventFilter(const QByteArray &eventType, void *message, long int *result) override;
+
 private:
     void init();
 

xwl/xwayland.cpp

@@ -187,10 +187,6 @@ void Xwayland::dispatchEvents()
     }
 
     while (xcb_generic_event_t *event = xcb_poll_for_event(connection)) {
-        if (m_dataBridge->filterEvent(event)) {
-            free(event);
-            continue;
-        }
         long result = 0;
         QAbstractEventDispatcher *dispatcher = QCoreApplication::eventDispatcher();
         dispatcher->filterNativeEvent(QByteArrayLiteral("xcb_generic_event_t"), event, &result);