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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/168836">168836</a></dd>

<dt>Author</dt> <dd>abucur@adobe.com</dd>

<dt>Date</dt> <dd>2014-05-14 07:35:07 -0700 (Wed, 14 May 2014)</dd>

</dl>

<h3>Log Message</h3>

<pre>[CSS Regions] Don't relayout when updating the region range unless necessary

https://bugs.webkit.org/show_bug.cgi?id=132120

Reviewed by Antti Koivisto.

The patch reduces the cases when a relayout is made for boxes that change the region range.

This lowers the amount of nested layouts in most cases and produces big layout speedups for trees

without overhanging floats.

Tests: Major performance improvement with speedups of 50-60% on:

Layout/RegionsAuto.html, Layout/RegionsAutoMaxHeight.html and Layout/RegionsFixed.html

* rendering/RenderBlock.cpp:

(WebCore::RenderBlock::updateRegionRangeForBoxChild): Ask the child box if it needs a relayout

in case its region range changes.

* rendering/RenderBlockFlow.cpp:

(WebCore::RenderBlockFlow::layoutBlockChild): It's not necessary to do two layouts here because

there's no block direction position change between them for the child.

(WebCore::RenderBlockFlow::needsLayoutAfterRegionRangeChange): If the block doesn't have floats

or if it expands to enclose the floats it doesn't need to relayout after a region range chage.

It's not possible for it to have a float inside overflow that must be repositioned using the new

range.

* rendering/RenderBlockFlow.h:

* rendering/RenderBox.h:

(WebCore::RenderBox::needsLayoutAfterRegionRangeChange): By default don't relayout after a region

range change.</pre>

<h3>Modified Paths</h3>

<ul>

<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>

<li><a href="#trunkSourceWebCorerenderingRenderBlockcpp">trunk/Source/WebCore/rendering/RenderBlock.cpp</a></li>

<li><a href="#trunkSourceWebCorerenderingRenderBlockFlowcpp">trunk/Source/WebCore/rendering/RenderBlockFlow.cpp</a></li>

<li><a href="#trunkSourceWebCorerenderingRenderBlockFlowh">trunk/Source/WebCore/rendering/RenderBlockFlow.h</a></li>

<li><a href="#trunkSourceWebCorerenderingRenderBoxh">trunk/Source/WebCore/rendering/RenderBox.h</a></li>

</ul>

</div>

<div id="patch">

<h3>Diff</h3>

<a id="trunkSourceWebCoreChangeLog"></a>

<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (168835 => 168836)</h4>

<pre class="diff"><span>

<span class="info">--- trunk/Source/WebCore/ChangeLog        2014-05-14 13:43:30 UTC (rev 168835)

+++ trunk/Source/WebCore/ChangeLog        2014-05-14 14:35:07 UTC (rev 168836)

</span><span class="lines">@@ -1,3 +1,32 @@

</span><ins>+2014-05-14  Andrei Bucur  &lt;abucur@adobe.com&gt;

+

+        [CSS Regions] Don't relayout when updating the region range unless necessary

+        https://bugs.webkit.org/show_bug.cgi?id=132120

+

+        Reviewed by Antti Koivisto.

+

+        The patch reduces the cases when a relayout is made for boxes that change the region range.

+        This lowers the amount of nested layouts in most cases and produces big layout speedups for trees

+        without overhanging floats.

+

+        Tests: Major performance improvement with speedups of 50-60% on:

+        Layout/RegionsAuto.html, Layout/RegionsAutoMaxHeight.html and Layout/RegionsFixed.html

+

+        * rendering/RenderBlock.cpp:

+        (WebCore::RenderBlock::updateRegionRangeForBoxChild): Ask the child box if it needs a relayout

+        in case its region range changes.

+        * rendering/RenderBlockFlow.cpp:

+        (WebCore::RenderBlockFlow::layoutBlockChild): It's not necessary to do two layouts here because

+        there's no block direction position change between them for the child.

+        (WebCore::RenderBlockFlow::needsLayoutAfterRegionRangeChange): If the block doesn't have floats

+        or if it expands to enclose the floats it doesn't need to relayout after a region range chage.

+        It's not possible for it to have a float inside overflow that must be repositioned using the new

+        range.

+        * rendering/RenderBlockFlow.h:

+        * rendering/RenderBox.h:

+        (WebCore::RenderBox::needsLayoutAfterRegionRangeChange): By default don't relayout after a region

+        range change.

+

</ins><span class="cx"> 2014-05-14  Antti Koivisto  &lt;antti@apple.com&gt;

</span><span class="cx"> 

</span><span class="cx">         RuleData should ref the StyleRule

</span></span></pre></div>

<a id="trunkSourceWebCorerenderingRenderBlockcpp"></a>

<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderBlock.cpp (168835 => 168836)</h4>

<pre class="diff"><span>

<span class="info">--- trunk/Source/WebCore/rendering/RenderBlock.cpp        2014-05-14 13:43:30 UTC (rev 168835)

+++ trunk/Source/WebCore/rendering/RenderBlock.cpp        2014-05-14 14:35:07 UTC (rev 168836)

</span><span class="lines">@@ -3966,10 +3966,14 @@

</span><span class="cx">     RenderRegion* newEndRegion = nullptr;

</span><span class="cx">     flowThread-&gt;getRegionRangeForBox(&amp;box, newStartRegion, newEndRegion);

</span><span class="cx"> 

</span><ins>+

+    // Changing the start region means we shift everything and a relayout is needed.

+    if (newStartRegion != startRegion)

+        return true;

+

</ins><span class="cx">     // The region range of the box has changed. Some boxes (e.g floats) may have been positioned assuming

<span class="cx">     // a different range.

<del>-    // FIXME: Be smarter about this. We don't need to relayout all the time.

-    if (newStartRegion != startRegion || newEndRegion != endRegion)

</del><ins>+    if (box.needsLayoutAfterRegionRangeChange() &amp;&amp; newEndRegion != endRegion)

</ins><span class="cx">         return true;

</span><span class="cx"> 

</span><span class="cx">     return false;

</span></span></pre></div>

<a id="trunkSourceWebCorerenderingRenderBlockFlowcpp"></a>

<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderBlockFlow.cpp (168835 => 168836)</h4>

<pre class="diff"><span>

<span class="info">--- trunk/Source/WebCore/rendering/RenderBlockFlow.cpp        2014-05-14 13:43:30 UTC (rev 168835)

+++ trunk/Source/WebCore/rendering/RenderBlockFlow.cpp        2014-05-14 14:35:07 UTC (rev 168836)

</span><span class="lines">@@ -746,16 +746,14 @@

</span><span class="cx">             if (!child.needsLayout())

</span><span class="cx">                 child.markForPaginationRelayoutIfNeeded();

</span><span class="cx">         }

</span><del>-

-        // Our guess was wrong. Make the child lay itself out again.

-        child.layoutIfNeeded();

</del><span class="cx">     }

</span><span class="cx"> 

</span><del>-    if (updateRegionRangeForBoxChild(child)) {

</del><ins>+    if (updateRegionRangeForBoxChild(child))

</ins><span class="cx">         child.setNeedsLayout(MarkOnlyThis);

</span><del>-        child.layoutIfNeeded();

-    }

</del><span class="cx"> 

<ins>+    // In case our guess was wrong, relayout the child.

+    child.layoutIfNeeded();

+

</ins><span class="cx">     // We are no longer at the top of the block if we encounter a non-empty child.  

<span class="cx">     // This has to be done after checking for clear, so that margins can be reset if a clear occurred.

</span><span class="cx">     if (marginInfo.atBeforeSideOfBlock() &amp;&amp; !child.isSelfCollapsingBlock())

</span><span class="lines">@@ -3003,6 +3001,17 @@

</span><span class="cx">     }

</span><span class="cx"> }

</span><span class="cx"> 

</span><ins>+bool RenderBlockFlow::needsLayoutAfterRegionRangeChange() const

+{

+    // A block without floats or that expands to enclose them won't need a relayout

+    // after a region range change. There is no overflow content needing relayout

+    // in the region chain because the region range can only shrink after the estimation.

+    if (!containsFloats() || expandsToEncloseOverhangingFloats())

+        return false;

+

+    return true;

+}

+

</ins><span class="cx"> bool RenderBlockFlow::canHaveChildren() const

</span><span class="cx"> {

</span><span class="cx">     return !renderNamedFlowFragment() ? RenderBlock::canHaveChildren() : renderNamedFlowFragment()-&gt;canHaveChildren();

</span></span></pre></div>

<a id="trunkSourceWebCorerenderingRenderBlockFlowh"></a>

<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderBlockFlow.h (168835 => 168836)</h4>

<pre class="diff"><span>

<span class="info">--- trunk/Source/WebCore/rendering/RenderBlockFlow.h        2014-05-14 13:43:30 UTC (rev 168835)

+++ trunk/Source/WebCore/rendering/RenderBlockFlow.h        2014-05-14 14:35:07 UTC (rev 168836)

</span><span class="lines">@@ -388,6 +388,8 @@

</span><span class="cx">     

</span><span class="cx">     void updateColumnProgressionFromStyle(RenderStyle*);

</span><span class="cx"> 

</span><ins>+    virtual bool needsLayoutAfterRegionRangeChange() const override;

+

</ins><span class="cx"> protected:

</span><span class="cx">     virtual void computeIntrinsicLogicalWidths(LayoutUnit&amp; minLogicalWidth, LayoutUnit&amp; maxLogicalWidth) const override;

</span><span class="cx">     

</span></span></pre></div>

<a id="trunkSourceWebCorerenderingRenderBoxh"></a>

<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderBox.h (168835 => 168836)</h4>

<pre class="diff"><span>

<span class="info">--- trunk/Source/WebCore/rendering/RenderBox.h        2014-05-14 13:43:30 UTC (rev 168835)

+++ trunk/Source/WebCore/rendering/RenderBox.h        2014-05-14 14:35:07 UTC (rev 168836)

</span><span class="lines">@@ -615,6 +615,7 @@

</span><span class="cx"> 

<span class="cx">     // True if this box can have a range in an outside fragmentation context.

</span><span class="cx">     bool canHaveOutsideRegionRange() const { return !isInFlowRenderFlowThread(); }

</span><ins>+    virtual bool needsLayoutAfterRegionRangeChange() const { return false; }

</ins><span class="cx"> 

</span><span class="cx"> protected:

</span><span class="cx">     RenderBox(Element&amp;, PassRef&lt;RenderStyle&gt;, unsigned baseTypeFlags);

</span></span></pre>

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