kwin: implement _KDE_NET_WM_OPAQUE_REGION

This patch implements an XProperty named _KDE_NET_WM_OPAQUE_REGION
which gives the compositor the information which part of a window
is opaque although it is an ARGB visual. The basic ideas are from
http://www.mail-archive.com/wm-spec-list@gnome.org/msg00715.html

Additionally the patch makes kwin  use this information to do a better
clipping in Scene::paintSimpleScreen which should result in a higher
performance.

REVIEW: 102933

atoms.cpp

@@ -120,6 +120,9 @@ Atoms::Atoms()
     atoms[n] = &kde_net_wm_shadow;
     names[n++] = (char*) "_KDE_NET_WM_SHADOW";
 
+    atoms[n] = &kde_net_wm_opaque_region;
+    names[n++] = (char*) "_KDE_NET_WM_OPAQUE_REGION";
+
     assert(n <= max);
 
     XInternAtoms(display(), names, n, false, atoms_return);

atoms.h

@@ -62,6 +62,7 @@ public:
     Atom net_wm_sync_request;
     Atom kde_net_wm_block_compositing;
     Atom kde_net_wm_shadow;
+    Atom kde_net_wm_opaque_region;
 };
 
 

events.cpp

@@ -1648,6 +1648,8 @@ void Toplevel::propertyNotifyEvent(XPropertyEvent* e)
             getWindowRole();
         else if (e->atom == atoms->kde_net_wm_shadow)
             getShadow();
+        else if (e->atom == atoms->kde_net_wm_opaque_region)
+            getWmOpaqueRegion();
         break;
     }
     emit propertyNotify(this, e->atom);

manage.cpp

@@ -136,6 +136,7 @@ bool Client::manage(Window w, bool isMapped)
     getWindowProtocols();
     getWmNormalHints(); // Get xSizeHint
     getMotifHints();
+    getWmOpaqueRegion();
 
     // TODO: Try to obey all state information from info->state()
 

scene.cpp

@@ -273,7 +273,15 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
             topw->resetRepaints(topw->shadow()->shadowRegion().boundingRect());
         }
         // Clip out the decoration for opaque windows; the decoration is drawn in the second pass
-        data.clip = w->isOpaque() ? w->clientShape().translated(w->x(), w->y()) : QRegion();
+        if (w->isOpaque()) {
+            // the window is fully opaque
+            data.clip = w->clientShape().translated(w->x(), w->y());
+        } else if (topw->hasAlpha() && topw->opacity() == 1.0) {
+            // the window is partially opaque
+            data.clip = (w->clientShape() & topw->opaqueRegion()).translated(w->x(), w->y());
+        } else {
+            data.clip = QRegion();
+        }
         data.quads = w->buildQuads();
         // preparation step
         effects->prePaintWindow(effectWindow(w), data, time_diff);
@@ -314,7 +322,9 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
         // a higher opaque window
         data->region -= allclips;
 
-        if (!(data->mask & PAINT_WINDOW_TRANSLUCENT)) {
+        // Here we rely on WindowPrePaintData::setTranslucent() to remove
+        // the clip if needed.
+        if (!data->clip.isEmpty()) {
             // clip away this region for all windows below this one
             allclips |= data->clip;
             // Paint the opaque window
@@ -326,7 +336,8 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
             data->region -= data->clip;
             // if prePaintWindow didn't change the clipping area we only have to paint
             // the decoration
-            if (data-> clip == data.key()->clientShape().translated(data.key()->x(), data.key()->y())) {
+            if ((data-> clip ^
+                 data.key()->clientShape().translated(data.key()->x(), data.key()->y())).isEmpty()) {
                 data->mask |= PAINT_DECORATION_ONLY;
             }
         }

toplevel.cpp

@@ -131,6 +131,7 @@ void Toplevel::copyToDeleted(Toplevel* c)
     client_machine = c->wmClientMachine(false);
     wmClientLeaderWin = c->wmClientLeader();
     window_role = c->windowRole();
+    opaque_region = c->opaqueRegion();
     // this needs to be done already here, otherwise 'c' could very likely
     // call discardWindowPixmap() in something called during cleanup
     c->window_pix = None;
@@ -396,6 +397,44 @@ const Shadow *Toplevel::shadow() const
     }
 }
 
+void Toplevel::getWmOpaqueRegion()
+{
+    const int length=32768;
+    unsigned long bytes_after_return=0;
+    QRegion new_opaque_region;
+    do {
+        unsigned long* data;
+        Atom type;
+        int rformat;
+        unsigned long nitems;
+        if (XGetWindowProperty(display(), client,
+                               atoms->kde_net_wm_opaque_region, 0, length, false, XA_CARDINAL,
+                               &type, &rformat, &nitems, &bytes_after_return,
+                               reinterpret_cast< unsigned char** >(&data)) == Success) {
+            if (type != XA_CARDINAL || rformat != 32 || nitems%4) {
+                // it can happen, that the window does not provide this property
+                XFree(data);
+                break;
+            }
+
+            for (unsigned int i = 0; i < nitems;) {
+                const int x = data[i++];
+                const int y = data[i++];
+                const int w = data[i++];
+                const int h = data[i++];
+
+                new_opaque_region += QRect(x,y,w,h);
+            }
+            XFree(data);
+        } else {
+            kWarning(1212) << "XGetWindowProperty failed";
+            break;
+        }
+    } while (bytes_after_return > 0);
+
+    opaque_region = new_opaque_region;
+}
+
 } // namespace
 
 #include "toplevel.moc"

toplevel.h

@@ -156,6 +156,13 @@ public:
      **/
     void getShadow();
 
+    /**
+     * This method returns the area that the Toplevel window reports to be opaque.
+     * It is supposed to only provide valueable information if @link hasAlpha is @c true .
+     * @see hasAlpha
+     **/
+    const QRegion& opaqueRegion() const;
+
 signals:
     void opacityChanged(KWin::Toplevel* toplevel, qreal oldOpacity);
     void damaged(KWin::Toplevel* toplevel, const QRect& damage);
@@ -177,6 +184,13 @@ protected:
     void addDamageFull();
     void getWmClientLeader();
     void getWmClientMachine();
+
+    /**
+     * This function fetches the opaque region from this Toplevel.
+     * Will only be called on corresponding property changes and for initialization.
+     **/
+    void getWmOpaqueRegion();
+
     void getResourceClass();
     void getWindowRole();
     virtual void debug(QDebug& stream) const = 0;
@@ -214,6 +228,7 @@ private:
     QByteArray window_role;
     bool unredirect;
     bool unredirectSuspend; // when unredirected, but pixmap is needed temporarily
+    QRegion opaque_region;
     // when adding new data members, check also copyToDeleted()
 };
 
@@ -397,6 +412,11 @@ inline bool Toplevel::hasAlpha() const
     return depth() == 32;
 }
 
+inline const QRegion& Toplevel::opaqueRegion() const
+{
+    return opaque_region;
+}
+
 inline
 EffectWindowImpl* Toplevel::effectWindow()
 {

unmanaged.cpp

@@ -72,6 +72,7 @@ bool Unmanaged::track(Window w)
     if (Extensions::shapeAvailable())
         XShapeSelectInput(display(), w, ShapeNotifyMask);
     detectShape(w);
+    getWmOpaqueRegion();
     setupCompositing();
     ungrabXServer();
     if (effects)