diff --git a/effects.cpp b/effects.cpp
index 8138af70cc..53c9327613 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -981,6 +981,11 @@ QRect EffectWindowImpl::geometry() const
     return toplevel->geometry();
     }
 
+QRegion EffectWindowImpl::shape() const
+    {
+    return sw ? sw->shape() : geometry();
+    }
+
 QSize EffectWindowImpl::size() const
     {
     return toplevel->size();
diff --git a/effects.h b/effects.h
index 3864b1578c..9d38860e03 100644
--- a/effects.h
+++ b/effects.h
@@ -183,6 +183,7 @@ class EffectWindowImpl : public EffectWindow
         virtual int width() const;
         virtual int height() const;
         virtual QRect geometry() const;
+        virtual QRegion shape() const;
         virtual QPoint pos() const;
         virtual QSize size() const;
         virtual QRect rect() const;
diff --git a/lib/kwineffects.h b/lib/kwineffects.h
index 667502721a..165c166cfe 100644
--- a/lib/kwineffects.h
+++ b/lib/kwineffects.h
@@ -490,6 +490,7 @@ class KWIN_EXPORT EffectWindow
         virtual int width() const = 0;
         virtual int height() const = 0;
         virtual QRect geometry() const = 0;
+        virtual QRegion shape() const = 0;
         virtual QPoint pos() const = 0;
         virtual QSize size() const = 0;
         virtual QRect rect() const = 0;
@@ -627,7 +628,14 @@ class KWIN_EXPORT WindowPrePaintData
     {
     public:
         int mask;
+        /**
+         * Region that will be painted, in screen coordinates.
+         **/
         QRegion paint;
+        /**
+         * The clip region will be substracted from paint region of following windows.
+         * I.e. window will definitely cover it's clip region
+         **/
         QRegion clip;
         WindowQuadList quads;
         /**