Introduce property "visible" on EffectWindow

This property can be used to check whether a window is currently visible
to the user, that is:
* not minimized
* on the current desktop
* on current activity

This is a common need for various effects.

REVIEW: 108341

effects/fallapart/fallapart.cpp

@@ -148,11 +148,7 @@ void FallApartEffect::slotWindowClosed(EffectWindow* c)
 {
     if (!isRealWindow(c))
         return;
-    if (c->isMinimized())
-        return;
-    if (!c->isOnCurrentDesktop())
-        return;
-    if (!c->isOnCurrentActivity())
+    if (!c->isVisible())
         return;
     const void* e = c->data(WindowClosedGrabRole).value<void*>();
     if (e && e != this)

libkwineffects/kwineffects.cpp

@@ -818,6 +818,13 @@ bool EffectWindow::hasDecoration() const
     return contentsRect() != QRect(0, 0, width(), height());
 }
 
+bool EffectWindow::isVisible() const
+{
+    return !isMinimized()
+           && isOnCurrentDesktop()
+           && isOnCurrentActivity();
+}
+
 
 //****************************************
 // EffectWindowGroup

libkwineffects/kwineffects.h

@@ -1360,6 +1360,16 @@ class KWIN_EXPORT EffectWindow : public QObject
      * @since 4.10
      **/
     Q_PROPERTY(bool decorationHasAlpha READ decorationHasAlpha)
+    /**
+     * Whether the window is currently visible to the user, that is:
+     * <ul>
+     * <li>Not minimized</li>
+     * <li>On current desktop</li>
+     * <li>On current activity</li>
+     * </ul>
+     * @since 4.11
+     **/
+    Q_PROPERTY(bool visible READ isVisible)
 public:
     /**  Flags explaining why painting should be disabled  */
     enum {
@@ -1577,6 +1587,11 @@ public:
 
     bool isCurrentTab() const;
 
+    /**
+     * @since 4.11
+     **/
+    bool isVisible() const;
+
     /**
      * Can be used to by effects to store arbitrary data in the EffectWindow.
      */