[plugins/qpa] Add a roundtrip platform function

Summary:
Mostly intended for plugins loaded into KWin and wanting to use
KWayland::Client::ConnectionThread::roundtrip(). By providing this
function we can ensure that KWin does not block and nevertheless
perform the required roundtrip.

Reviewers: #plasma

Subscribers: plasma-devel

Projects: #plasma

Differential Revision: https://phabricator.kde.org/D1153

plugins/qpa/nativeinterface.cpp

@@ -79,5 +79,26 @@ void *NativeInterface::nativeResourceForWindow(const QByteArray &resource, QWind
     return nullptr;
 }
 
+static void roundtrip()
+{
+    if (!waylandServer()) {
+        return;
+    }
+    auto c = waylandServer()->internalClientConection();
+    if (!c) {
+        return;
+    }
+    c->flush();
+    waylandServer()->dispatch();
+}
+
+QFunctionPointer NativeInterface::platformFunction(const QByteArray &function) const
+{
+    if (qstrcmp(function.toLower(), "roundtrip") == 0) {
+        return &roundtrip;
+    }
+    return nullptr;
+}
+
 }
 }

plugins/qpa/nativeinterface.h

@@ -35,6 +35,7 @@ public:
     explicit NativeInterface(Integration *integration);
     void *nativeResourceForIntegration(const QByteArray &resource) override;
     void *nativeResourceForWindow(const QByteArray &resourceString, QWindow *window) override;
+    QFunctionPointer platformFunction(const QByteArray &function) const override;
 
 private:
     Integration *m_integration;