Remove unnecessary checks in PaintLayer::backgroundIsKnownToBeOpaqueInRect

third_party/WebKit/Source/core/paint/PaintLayer.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 2379 matching lines @@
     return m_rareData && m_rareData->compositedLayerMapping && m_rareData->compositedLayerMapping->hasChildClippingMaskLayer();
 }
 
 bool PaintLayer::paintsWithTransform(GlobalPaintFlags globalPaintFlags) const
 {
     return (transform() || layoutObject()->style()->position() == FixedPosition) && ((globalPaintFlags & GlobalPaintFlattenCompositingLayers) || compositingState() != PaintsIntoOwnBacking);
 }
 
 bool PaintLayer::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) const
 {
-    if (!isSelfPaintingLayer() && !hasSelfPaintingLayerDescendant())

[chrishtr, 2016/08/30 20:49:01]

childBackgroundIsKnownToBeOpaqueInRect calls backgroundIsKnownToBeOpaqueInRect
on all stacking-children
PaintLayers that paint into the same backing. They don't have to be
self-painting, right?

[Stephen Chennney, 2016/08/30 20:58:51]

Right, in fact we only want the ones that are not self painting, because self
painters contribute to a different backing. That check already exists in
childBackgroundIsKnownToBeOpaqueInRect, in the form of
childLayer->isPaintInvalidationContainer()

[chrishtr, 2016/08/30 21:15:39]

No. self-painting is not the same thing as independently composited.
self-painting means something
sort of like stacking context.

-        return false;
-
     if (paintsWithTransparency(GlobalPaintNormalPhase))
         return false;
 
     // We can't use hasVisibleContent(), because that will be true if our layoutObject is hidden, but some child
     // is visible and that child doesn't cover the entire rect.
     if (layoutObject()->style()->visibility() != EVisibility::Visible)
         return false;
 
     if (paintsWithFilters() && layoutObject()->style()->filter().hasFilterThatAffectsOpacity())
         return false;
 
     // FIXME: Handle simple transforms.
     if (paintsWithTransform(GlobalPaintNormalPhase))
         return false;
 
-    // FIXME: Remove this check.
     // This function should not be called when layer-lists are dirty.
-    // It is somehow getting triggered during style update.
-    if (m_stackingNode->zOrderListsDirty())
-        return false;
+    DCHECK(!m_stackingNode->zOrderListsDirty());
 
     // FIXME: We currently only check the immediate layoutObject,
-    // which will miss many cases.
+    // which will miss many cases where additional layout objects paint
+    // into this layer.
     if (layoutObject()->backgroundIsKnownToBeOpaqueInRect(localRect))
         return true;
 
     // We can't consult child layers if we clip, since they might cover
     // parts of the rect that are clipped out.
     if (layoutObject()->hasClipRelatedProperty())
         return false;
 
     return childBackgroundIsKnownToBeOpaqueInRect(localRect);
 }
@@ skipping 512 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif