Connect ThumbnailItem to Compositor::compositingToggled

If a KWin script uses a ThumbnailItem which gets created before the
Compositor is fully initialized the thumbnail is not shown at all because
the connect to windowAdded etc. will never happen.

Therefore connect to Compositor::compositingToggled to re-connect
whenever the compositing state changes.

REVIEW: 109310

thumbnailitem.cpp

@@ -23,6 +23,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "client.h"
 #include "effects.h"
 #include "workspace.h"
+#include "composite.h"
 // Qt
 #include <QtDeclarative/QDeclarativeContext>
 #include <QtDeclarative/QDeclarativeEngine>
@@ -40,10 +41,9 @@ ThumbnailItem::ThumbnailItem(QDeclarativeItem* parent)
     , m_parentWindow(0)
 {
     setFlags(flags() & ~QGraphicsItem::ItemHasNoContents);
-    if (effects) {
-        connect(effects, SIGNAL(windowAdded(KWin::EffectWindow*)), SLOT(effectWindowAdded()));
-        connect(effects, SIGNAL(windowDamaged(KWin::EffectWindow*,QRect)), SLOT(repaint(KWin::EffectWindow*)));
-    }
+    Q_ASSERT(Compositor::isCreated());
+    connect(Compositor::self(), SIGNAL(compositingToggled(bool)), SLOT(compositingToggled()));
+    compositingToggled();
     QTimer::singleShot(0, this, SLOT(init()));
 }
 
@@ -51,6 +51,16 @@ ThumbnailItem::~ThumbnailItem()
 {
 }
 
+void ThumbnailItem::compositingToggled()
+{
+    m_parent.clear();
+    if (effects) {
+        connect(effects, SIGNAL(windowAdded(KWin::EffectWindow*)), SLOT(effectWindowAdded()));
+        connect(effects, SIGNAL(windowDamaged(KWin::EffectWindow*,QRect)), SLOT(repaint(KWin::EffectWindow*)));
+        effectWindowAdded();
+    }
+}
+
 void ThumbnailItem::init()
 {
     findParentEffectWindow();

thumbnailitem.h

@@ -60,6 +60,7 @@ private Q_SLOTS:
     void init();
     void effectWindowAdded();
     void repaint(KWin::EffectWindow* w);
+    void compositingToggled();
 private:
     void findParentEffectWindow();
     qulonglong m_wId;