Fixes: NB#189519 - compositor calls eglSwapBuffers without rendering anything

- keep non-composited mode when we don't have mapped windows to paint
- avoid updating the scene if we don't need to

4 files changed, 35 insertions, 9 deletions

diff --git a/src/mcompositemanager.cpp b/src/mcompositemanager.cpp
index 5873592..f57e525 100644
--- a/src/mcompositemanager.cpp
+++ b/src/mcompositemanager.cpp
@@ -1075,6 +1075,17 @@ MCompositeWindow *MCompositeManagerPrivate::getHighestDecorated()
     return 0;
 }
 
+bool MCompositeManagerPrivate::haveMappedWindow() const
+{
+    for (int i = stacking_list.size() - 1; i >= 0; --i) {
+        Window w = stacking_list.at(i);        
+        MWindowPropertyCache *pc = prop_caches.value(w, 0);
+        if (pc && pc->is_valid && pc->isMapped())
+            return true;
+    }
+    return false;
+}
+
 // TODO: merge this with disableCompositing() so that in the end we have
 // stacking order sensitive logic
 bool MCompositeManagerPrivate::possiblyUnredirectTopmostWindow()
@@ -1121,6 +1132,10 @@ bool MCompositeManagerPrivate::possiblyUnredirectTopmostWindow()
         if (pc && pc->is_valid && pc->beingMapped())
             return false;
     }
+    if (!haveMappedWindow()) {
+        disableCompositing(FORCED);
+        return true;
+    }
 
     if (top && cw && !MCompositeWindow::hasTransitioningWindow()) {
         // unredirect the chosen window and any docks and OR windows above it
@@ -2654,7 +2669,8 @@ void MCompositeManagerPrivate::displayOff(bool display_off)
 {
     if (display_off) {
         // keep compositing to have synthetic events to obscure all windows
-        enableCompositing(true);
+        if (!haveMappedWindow())
+            enableCompositing(true);
         scene()->views()[0]->setUpdatesEnabled(false);
         /* stop pinging to save some battery */
         for (QHash<Window, MCompositeWindow *>::iterator it = windows.begin();
@@ -2666,7 +2682,6 @@ void MCompositeManagerPrivate::displayOff(bool display_off)
                  i->propertyCache()->damageTracking(false);
         }
     } else {
-        scene()->views()[0]->setUpdatesEnabled(true);
         if (!possiblyUnredirectTopmostWindow())
             enableCompositing(false);
         /* start pinging again */
@@ -2960,7 +2975,6 @@ void MCompositeManagerPrivate::redirectWindows()
     }
     if (kids)
         XFree(kids);
-    scene()->views()[0]->setUpdatesEnabled(true);
 
     // Wait for the MapNotify for the overlay (show() of the graphicsview
     // in main() causes it even if we don't map it explicitly)
@@ -3281,7 +3295,7 @@ void MCompositeManagerPrivate::enableRedirection()
     compositing = true;
     // no delay: application does not need to redraw when maximizing it
     scene()->views()[0]->setUpdatesEnabled(true);
-    glwidget->update();
+    // NOTE: enableRedirectedRendering() calls glwidget->update() if needed
     // At this point everything should be rendered off-screen
     emit compositingEnabled();
 }
diff --git a/src/mcompositemanager_p.h b/src/mcompositemanager_p.h
index e2750e1..c45f2b6 100644
--- a/src/mcompositemanager_p.h
+++ b/src/mcompositemanager_p.h
@@ -107,6 +107,7 @@ public:
     Window getLastVisibleParent(MWindowPropertyCache *pc);
 
     bool possiblyUnredirectTopmostWindow();
+    bool haveMappedWindow() const;
     bool isRedirected(Window window);
     bool x11EventFilter(XEvent *event);
     bool processX11EventFilters(XEvent *event, bool after);
diff --git a/src/mcompositewindow.cpp b/src/mcompositewindow.cpp
index 33c733c..c025834 100644
--- a/src/mcompositewindow.cpp
+++ b/src/mcompositewindow.cpp
@@ -687,8 +687,13 @@ QVariant MCompositeWindow::itemChange(GraphicsItemChange change, const QVariant
         p->d->setWindowDebugProperties(window());
     }
     
+    /* disabled to avoid glSwapBuffers call without painting any item (Qt bug)
+     * see NB#189519
     if (zvalChanged || change == ItemVisibleHasChanged || change == ItemParentHasChanged)
+    {
         p->d->glwidget->update();
+    }
+    */
 
     return QGraphicsItem::itemChange(change, value);
 }
@@ -753,7 +758,10 @@ QPainterPath MCompositeWindow::shape() const
 Window MCompositeWindow::lastVisibleParent() const
 {
     MCompositeManager *p = (MCompositeManager *) qApp;
-    return p->d->getLastVisibleParent(propertyCache());
+    if (pc && pc->is_valid)
+        return p->d->getLastVisibleParent(pc);
+    else
+        return None;
 }
 
 int MCompositeWindow::indexInStack() const
diff --git a/src/mtexturepixmapitem_egl.cpp b/src/mtexturepixmapitem_egl.cpp
index 9272452..7ba56ac 100644
--- a/src/mtexturepixmapitem_egl.cpp
+++ b/src/mtexturepixmapitem_egl.cpp
@@ -258,6 +258,7 @@ void MTexturePixmapItem::updateWindowPixmap(XRectangle *rects, int num)
         r += QRegion(rects[i].x, rects[i].y, rects[i].width, rects[i].height);
     d->damageRegion = r;
     
+    bool new_image = false;
     if (d->custom_tfp) {
         QPixmap qp = QPixmap::fromX11Pixmap(d->windowp);
         
@@ -265,11 +266,13 @@ void MTexturePixmapItem::updateWindowPixmap(XRectangle *rects, int num)
         glBindTexture(GL_TEXTURE_2D, d->textureId);
         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, img.width(), 
                         img.height(), GL_RGBA, GL_UNSIGNED_BYTE, img.bits());
-    } else {
-        if (d->egl_image == EGL_NO_IMAGE_KHR)
-            saveBackingStore();
+        new_image = true;
+    } else if (d->egl_image == EGL_NO_IMAGE_KHR) {
+        saveBackingStore();
+        new_image = true;
     }    
-    d->glwidget->update();
+    if (new_image || !d->damageRegion.isEmpty())
+        d->glwidget->update();
 }
 
 void MTexturePixmapItem::paint(QPainter *painter,