Simply rules for compositing fixed position elements

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1275 matching lines @@
         // Fixed items should always have layers.
         ASSERT(renderer->hasLayer());
         RenderLayer* layer = toRenderBoxModelObject(renderer)->layer();
 
         // Layers that paint into their ancestor or into a grouped backing will still need
         // to apply a paint invalidation. If the layer paints into its own backing, then
         // it does not need paint invalidation just to scroll.
         if (layer->compositingState() == PaintsIntoOwnBacking)
             continue;
 
-        if (layer->viewportConstrainedNotCompositedReason() == RenderLayer::NotCompositedForBoundsOutOfView
-            || layer->viewportConstrainedNotCompositedReason() == RenderLayer::NotCompositedForNoVisibleContent) {
-            // Don't invalidate for invisible fixed layers.
-            continue;
-        }
-
         if (layer->hasAncestorWithFilterOutsets()) {
             // If the fixed layer has a blur/drop-shadow filter applied on at least one of its parents, we cannot
             // scroll using the fast path, otherwise the outsets of the filter will be moved around the page.
             return false;
         }
 
         IntRect updateRect = pixelSnappedIntRect(layer->repainter().repaintRectIncludingNonCompositingDescendants());
 
         const RenderLayerModelObject* repaintContainer = layer->renderer()->containerForPaintInvalidation();
         if (repaintContainer && !repaintContainer->isRenderView()) {
@@ skipping 287 matching lines @@
 
         // Fixed items should always have layers.
         ASSERT(renderer->hasLayer());
 
         RenderLayer* layer = toRenderBoxModelObject(renderer)->layer();
 
         // Don't need to do this for composited fixed items.
         if (layer->compositingState() == PaintsIntoOwnBacking)
             continue;
 
-        // Also don't need to do this for invisible items.
-        if (layer->viewportConstrainedNotCompositedReason() == RenderLayer::NotCompositedForBoundsOutOfView
-            || layer->viewportConstrainedNotCompositedReason() == RenderLayer::NotCompositedForNoVisibleContent)
-            continue;
-
         layer->repainter().computeRepaintRectsIncludingNonCompositingDescendants();
     }
 }
 
 void FrameView::updateCompositedSelectionBoundsIfNeeded()
 {
     if (!RuntimeEnabledFeatures::compositedSelectionUpdatesEnabled())
         return;
 
     Page* page = frame().page();
@@ skipping 1583 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace blink