Simply rules for compositing fixed position elements

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 110 matching lines @@
     , m_has3DTransformedDescendant(false)
     , m_containsDirtyOverlayScrollbars(false)
     , m_hasFilterInfo(false)
     , m_needsAncestorDependentCompositingInputsUpdate(true)
     , m_needsDescendantDependentCompositingInputsUpdate(true)
     , m_childNeedsCompositingInputsUpdate(true)
     , m_hasCompositingDescendant(false)
     , m_hasNonCompositedChild(false)
     , m_shouldIsolateCompositedDescendants(false)
     , m_lostGroupedMapping(false)
-    , m_viewportConstrainedNotCompositedReason(NoNotCompositedReason)
     , m_renderer(renderer)
     , m_parent(0)
     , m_previous(0)
     , m_next(0)
     , m_first(0)
     , m_last(0)
     , m_staticInlinePosition(0)
     , m_staticBlockPosition(0)
     , m_enclosingPaginationLayer(0)
     , m_potentialCompositingReasonsFromStyle(CompositingReasonNone)
@@ skipping 1520 matching lines @@
     DisableCompositingQueryAsserts disabler;
 
     if (compositingState() != NotComposited) {
         if (context->updatingControlTints() || (paintingInfo.paintBehavior & PaintBehaviorFlattenCompositingLayers)) {
             // The updatingControlTints() painting pass goes through compositing layers,
             // but we need to ensure that we don't cache clip rects computed with the wrong root in this case.
             // FIXME: ok, but what about PaintBehaviorFlattenCompositingLayers? That's for printing.
             // FIXME: why isn't the code here global, as opposed to being set on each paintLayer() call?
             paintFlags |= PaintLayerUncachedClipRects;
         }
-    } else if (viewportConstrainedNotCompositedReason() == NotCompositedForBoundsOutOfView) {
-        // Don't paint out-of-view viewport constrained layers (when doing prepainting) because they will never be visible
-        // unless their position or viewport size is changed.
-        return;
     }
 
     // Non self-painting leaf layers don't need to be painted as their renderer() should properly paint itself.
     if (!isSelfPaintingLayer() && !hasSelfPaintingLayerDescendant())
         return;
 
     if (shouldSuppressPaintingLayer(this))
         return;
 
     // If this layer is totally invisible then there is nothing to paint.
@@ skipping 2049 matching lines @@
         } else {
             rect.append(logicalBoundingBox());
             rects.set(this, rect);
         }
     }
 }
 
 DisableCompositingQueryAsserts::DisableCompositingQueryAsserts()
     : m_disabler(gCompositingQueryMode, CompositingQueriesAreAllowed) { }
 
-COMPILE_ASSERT(1 << RenderLayer::ViewportConstrainedNotCompositedReasonBits >= RenderLayer::NumNotCompositedReasons, too_many_viewport_constrained_not_compositing_reasons);
-
 } // namespace blink
 
 #ifndef NDEBUG
 void showLayerTree(const blink::RenderLayer* layer)
 {
     if (!layer)
         return;
 
     if (blink::LocalFrame* frame = layer->renderer()->frame()) {
         WTF::String output = externalRepresentation(frame, blink::RenderAsTextShowAllLayers | blink::RenderAsTextShowLayerNesting | blink::RenderAsTextShowCompositedLayers | blink::RenderAsTextShowAddresses | blink::RenderAsTextShowIDAndClass | blink::RenderAsTextDontUpdateLayout | blink::RenderAsTextShowLayoutState);
         fprintf(stderr, "%s\n", output.utf8().data());
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif