[effects/fallapart] Fix flickering problem

Summary:
The Fall Apart effect doesn't grab windows so a conflict could happen
if an alternative window open/close animation effect is enabled(e.g.
Fade, Glide).

### Before

{F5912324}

//Fall apart and Fade conflict with each other.//

### After

{F5912325}

//Only Fall apart animates the disappearing of System Settings.//

Test Plan:
* Enabled fall apart effect and fade effect
* Closed a window

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13527

effects/fallapart/fallapart.cpp

@@ -38,6 +38,7 @@ FallApartEffect::FallApartEffect()
     reconfigure(ReconfigureAll);
     connect(effects, SIGNAL(windowClosed(KWin::EffectWindow*)), this, SLOT(slotWindowClosed(KWin::EffectWindow*)));
     connect(effects, SIGNAL(windowDeleted(KWin::EffectWindow*)), this, SLOT(slotWindowDeleted(KWin::EffectWindow*)));
+    connect(effects, SIGNAL(windowDataChanged(KWin::EffectWindow*,int)), this, SLOT(slotWindowDataChanged(KWin::EffectWindow*,int)));
 }
 
 void FallApartEffect::reconfigure(ReconfigureFlags)
@@ -157,6 +158,7 @@ void FallApartEffect::slotWindowClosed(EffectWindow* c)
     const void* e = c->data(WindowClosedGrabRole).value<void*>();
     if (e && e != this)
         return;
+    c->setData(WindowClosedGrabRole, QVariant::fromValue(static_cast<void*>(this)));
     windows[ c ] = 0;
     c->refWindow();
 }
@@ -166,6 +168,25 @@ void FallApartEffect::slotWindowDeleted(EffectWindow* c)
     windows.remove(c);
 }
 
+void FallApartEffect::slotWindowDataChanged(EffectWindow* w, int role)
+{
+    if (role != WindowClosedGrabRole) {
+        return;
+    }
+
+    if (w->data(role).value<void*>() == this) {
+        return;
+    }
+
+    auto it = windows.find(w);
+    if (it == windows.end()) {
+        return;
+    }
+
+    it.key()->unrefWindow();
+    windows.erase(it);
+}
+
 bool FallApartEffect::isActive() const
 {
     return !windows.isEmpty();

effects/fallapart/fallapart.h

@@ -54,9 +54,10 @@ public:
 public Q_SLOTS:
     void slotWindowClosed(KWin::EffectWindow *c);
     void slotWindowDeleted(KWin::EffectWindow *w);
+    void slotWindowDataChanged(KWin::EffectWindow *w, int role);
 
 private:
-    QHash< const EffectWindow*, double > windows;
+    QHash< EffectWindow*, double > windows;
     bool isRealWindow(EffectWindow* w);
     int blockSize;
 };