kwin: make decoration repaints window-specific

This gives the new Scene::paintSimpleScreen more room for optimizations.

client.cpp

@@ -500,8 +500,9 @@ void Client::repaintDecorationPending()
         // The scene will update the decoration pixmaps in the next painting pass
         // if it has not been already repainted before
         const QRegion r = paintRedirector->scheduledRepaintRegion();
-        if (!r.isEmpty())
+        if (!r.isEmpty()) {
-            Workspace::self()->addRepaint(r.translated(x() - padding_left, y() - padding_top));
+            addRepaint(r.translated(-padding_left,-padding_top));
+        }
     }
 }
 

composite.cpp

@@ -748,6 +748,14 @@ void Toplevel::addRepaint(int x, int y, int w, int h)
     workspace()->checkCompositeTimer();
 }
 
+void Toplevel::addRepaint(const QRegion& r)
+{
+    if (!compositing())
+        return;
+    repaints_region += r;
+    workspace()->checkCompositeTimer();
+}
+
 void Toplevel::addRepaintFull()
 {
     repaints_region = decorationRect();

toplevel.h

@@ -124,6 +124,7 @@ public:
     bool unredirected() const;
     void suspendUnredirect(bool suspend);
     void addRepaint(const QRect& r);
+    void addRepaint(const QRegion& r);
     void addRepaint(int x, int y, int w, int h);
     virtual void addRepaintFull();
     // these call workspace->addRepaint(), but first transform the damage if needed