Update should paint flag when a float's composited scrolling status changes

third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 2027 matching lines @@
     if (!hasOverhangingFloats())
         return;
 
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator end = floatingObjectSet.end();
     for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
         const FloatingObject& floatingObject = *it->get();
         // Only issue paint invaldiations for the object if it is overhanging, is not in its own layer, and
         // is our responsibility to paint (m_shouldPaint is set). When paintAllDescendants is true, the latter
         // condition is replaced with being a descendant of us.
-        if (logicalBottomForFloat(floatingObject) > logicalHeight()
+        if (isOverhangingFloat(floatingObject)
             && !floatingObject.layoutObject()->hasSelfPaintingLayer()
             && (floatingObject.shouldPaint() || (paintAllDescendants && floatingObject.layoutObject()->isDescendantOf(this)))) {
 
             LayoutBox* floatingLayoutBox = floatingObject.layoutObject();
             floatingLayoutBox->setShouldDoFullPaintInvalidation();
             floatingLayoutBox->invalidatePaintForOverhangingFloats(false);
         }
     }
 }
 
@@ skipping 395 matching lines @@
 bool LayoutBlockFlow::hasOverhangingFloat(LayoutBox* layoutBox)
 {
     if (!m_floatingObjects || !parent())
         return false;
 
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(layoutBox);
     if (it == floatingObjectSet.end())
         return false;
 
-    return logicalBottomForFloat(*it->get()) > logicalHeight();
+    return isOverhangingFloat(**it);
 }
 
 void LayoutBlockFlow::addIntrudingFloats(LayoutBlockFlow* prev, LayoutUnit logicalLeftOffset, LayoutUnit logicalTopOffset)
 {
     ASSERT(!avoidsFloats());
 
     // If we create our own block formatting context then our contents don't interact with floats outside it, even those from our parent.
     if (createsNewFormattingContext())
         return;
 
@@ skipping 146 matching lines @@
 }
 
 LayoutUnit LayoutBlockFlow::logicalRightFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit logicalHeight) const
 {
     if (m_floatingObjects && m_floatingObjects->hasRightObjects())
         return m_floatingObjects->logicalRightOffset(fixedOffset, logicalTop, logicalHeight);
 
     return fixedOffset;
 }
 
+void LayoutBlockFlow::setAncestorShouldPaintFloatingObject(const LayoutBox& floatBox, bool shouldPaint)
+{
+    ASSERT(floatBox.isFloating());
+    ASSERT(!floatBox.hasSelfPaintingLayer());
+    for (LayoutObject* ancestor = floatBox.parent(); ancestor && ancestor->isLayoutBlockFlow(); ancestor = ancestor->parent()) {
+        LayoutBlockFlow* ancestorBlock = toLayoutBlockFlow(ancestor);
+        FloatingObjects* ancestorFloatingObjects = ancestorBlock->m_floatingObjects.get();
+        if (!ancestorFloatingObjects)
+            break;
+        FloatingObjectSet::iterator it = ancestorFloatingObjects->set().find<FloatingObjectHashTranslator>(const_cast<LayoutBox*>(&floatBox));
+        if (it == ancestorFloatingObjects->set().end())
+            break;
+
+        FloatingObject& floatingObject = **it;
+        if (shouldPaint) {
+            ASSERT(!floatingObject.shouldPaint());
+            if (ancestorBlock->hasSelfPaintingLayer() || !ancestorBlock->isOverhangingFloat(floatingObject)) {

[chrishtr, 2016/02/02 20:49:40]

Please paste your explanatory comment here:

The rules of float painting are:
- Let the nearest enclosing block in which the float doesn't overhang paint the
float;
- Or even if the float overhangs, if the block has self-painting layer, the
block paints the float.

[Xianzhu, 2016/02/02 22:47:12]

Done.

+                floatingObject.setShouldPaint(true);
+                return;
+            }
+        } else if (floatingObject.shouldPaint()) {
+            floatingObject.setShouldPaint(false);
+            return;
+        }
+    }
+    // We should have found the ancestor to update shouldPaint flag.
+    ASSERT_NOT_REACHED();
+}
+
 IntRect alignSelectionRectToDevicePixels(LayoutRect& rect)
 {
     LayoutUnit roundedX = LayoutUnit(rect.x().round());
     return IntRect(roundedX, rect.y().round(),
         (rect.maxX() - roundedX).round(),
         snapSizeToPixel(rect.height(), rect.y()));
 }
 
 bool LayoutBlockFlow::allowsPaginationStrut() const
 {
@@ skipping 194 matching lines @@
     FrameView* frameView = document().view();
     LayoutUnit top = LayoutUnit((style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height());
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (size().height() < visibleHeight)
         top += (visibleHeight - size().height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }
 
 } // namespace blink