[New Multicolumn] Create RenderMultiColumnSet during renderer creation, not during layout.

Source/core/rendering/RenderMultiColumnFlowThread.cpp

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 34 matching lines @@
 }
 
 RenderMultiColumnFlowThread* RenderMultiColumnFlowThread::createAnonymous(Document& document, RenderStyle* parentStyle)
 {
     RenderMultiColumnFlowThread* renderer = new RenderMultiColumnFlowThread();
     renderer->setDocumentForAnonymous(&document);
     renderer->setStyle(RenderStyle::createAnonymousStyleWithDisplay(parentStyle, BLOCK));
     return renderer;
 }
 
+RenderMultiColumnSet* RenderMultiColumnFlowThread::firstMultiColumnSet() const
+{
+    for (RenderObject* sibling = nextSibling(); sibling; sibling = sibling->nextSibling()) {
+        if (sibling->isRenderMultiColumnSet())
+            return toRenderMultiColumnSet(sibling);
+    }
+    return 0;
+}
+
+RenderMultiColumnSet* RenderMultiColumnFlowThread::lastMultiColumnSet() const
+{
+    for (RenderObject* sibling = multiColumnBlockFlow()->lastChild(); sibling; sibling = sibling->previousSibling()) {
+        if (sibling->isRenderMultiColumnSet())
+            return toRenderMultiColumnSet(sibling);
+    }
+    return 0;
+}
+
+void RenderMultiColumnFlowThread::addChild(RenderObject* newChild, RenderObject* beforeChild)
+{
+    RenderBlockFlow::addChild(newChild, beforeChild);
+    if (firstMultiColumnSet())
+        return;
+
+    // For now we only create one column set. It's created as soon as the multicol container gets
+    // any content at all.
+    RenderMultiColumnSet* newSet = RenderMultiColumnSet::createAnonymous(this, multiColumnBlockFlow()->style());
+    multiColumnBlockFlow()->RenderBlock::addChild(newSet);

[ojan, 2014/04/24 21:38:43]

Why do we need the RenderBlock version? Can the multiColumnBlockFlow() have a
flowThread? In either case, this might deserve a comment.

[mstensho (USE GERRIT), 2014/04/24 22:22:22]

Yes, multiColumnBlockFlow() is the one that has a flow thread, so if we use
RenderBlockFlow::addChild(), we'd get redirected right back here. Would cause an
infinite recursion.

Anyway, worth a comment. Done.

+    invalidateRegions();
+}
+
 void RenderMultiColumnFlowThread::populate()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
     ASSERT(!nextSibling());
     // Reparent children preceding the flow thread into the flow thread. It's multicol content
     // now. At this point there's obviously nothing after the flow thread, but renderers (column
     // sets and spanners) will be inserted there as we insert elements into the flow thread.
     multicolContainer->moveChildrenTo(this, multicolContainer->firstChild(), this, true);
 }
 
 void RenderMultiColumnFlowThread::evacuateAndDestroy()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
 
     // Remove all sets.
-    for (RenderBox* sibling = nextSiblingBox(); sibling;) {
-        RenderBox* nextSibling = sibling->nextSiblingBox();
-        if (sibling->isRenderMultiColumnSet())
-            sibling->destroy();
-        sibling = nextSibling;
-    }
+    while (RenderMultiColumnSet* columnSet = firstMultiColumnSet())

[ojan, 2014/04/24 21:38:43]

How do we have multiple sets? It looks like addChild will only ever create one.
From your comment above it sounds like maybe in the future we'll have multiple,
but if that's the case, maybe we could add the loops (here and below) then?

[mstensho (USE GERRIT), 2014/04/24 22:22:22]

For now, only one set. In the (near) future, we can have multiple sets, because
of spanners. This is already a while-loop, so I'm not sure I understand what you
mean.

If by "below" you mean the for-loop in layoutColumns(), I agree. I missed
updating that one. Will fix.

[ojan, 2014/04/24 22:46:59]

It's just a bit weird to me to have a while loop that never loops. But, it's
true that it was a loop before as well and it will soon loop. So it's fine. If I
were doing this, I'd add the while back in when adding spanners, but I don't
feel strongly about this.

+        columnSet->destroy();
 
     ASSERT(!previousSibling());
     ASSERT(!nextSibling());
 
     // Finally we can promote all flow thread's children. Before we move them to the flow thread's
     // container, we need to unregister the flow thread, so that they aren't just re-added again to
     // the flow thread that we're trying to empty.
     multicolContainer->resetMultiColumnFlowThread();
     moveAllChildrenTo(multicolContainer, true);
 
@@ skipping 74 matching lines @@
 {
     if (!m_needsRebalancing)
         return false;
 
     // Column heights may change here because of balancing. We may have to do multiple layout
     // passes, depending on how the contents is fitted to the changed column heights. In most
     // cases, laying out again twice or even just once will suffice. Sometimes we need more
     // passes than that, though, but the number of retries should not exceed the number of
     // columns, unless we have a bug.
     bool needsRelayout = false;
-    for (RenderBox* childBox = multiColumnBlockFlow()->firstChildBox(); childBox; childBox = childBox->nextSiblingBox()) {
-        if (childBox != this && childBox->isRenderMultiColumnSet()) {
-            RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(childBox);
-            if (multicolSet->recalculateBalancedHeight(!m_inBalancingPass)) {
-                multicolSet->setChildNeedsLayout(MarkOnlyThis);
-                needsRelayout = true;
-            }
+    for (RenderMultiColumnSet* multicolSet = firstMultiColumnSet(); multicolSet; multicolSet = multicolSet->nextSiblingMultiColumnSet()) {
+        if (multicolSet->recalculateBalancedHeight(!m_inBalancingPass)) {
+            multicolSet->setChildNeedsLayout(MarkOnlyThis);
+            needsRelayout = true;
         }
     }
 
     if (needsRelayout)
         setChildNeedsLayout(MarkOnlyThis);
 
     m_inBalancingPass = needsRelayout;
     return needsRelayout;
 }
 
 const char* RenderMultiColumnFlowThread::renderName() const
 {
     return "RenderMultiColumnFlowThread";
 }
 
+void RenderMultiColumnFlowThread::addRegionToThread(RenderRegion* renderRegion)
+{
+    RenderMultiColumnSet* columnSet = toRenderMultiColumnSet(renderRegion);
+    if (RenderMultiColumnSet* nextSet = columnSet->nextSiblingMultiColumnSet()) {
+        RenderRegionList::iterator it = m_regionList.find(nextSet);
+        ASSERT(it != m_regionList.end());
+        m_regionList.insertBefore(it, columnSet);
+    } else {
+        m_regionList.add(columnSet);
+    }
+    renderRegion->setIsValid(true);
+}
+
+void RenderMultiColumnFlowThread::willBeRemovedFromTree()
+{
+    // Detach all column sets from the flow thread. Cannot destroy them at this point, since they
+    // are siblings of this object, and there may be pointers to this object's sibling somewhere
+    // further up on the call stack.
+    for (RenderMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet())
+        columnSet->detachRegion();
+    multiColumnBlockFlow()->resetMultiColumnFlowThread();
+    RenderFlowThread::willBeRemovedFromTree();
+}
+
 void RenderMultiColumnFlowThread::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
 {
     // We simply remain at our intrinsic height.
     computedValues.m_extent = logicalHeight;
     computedValues.m_position = logicalTop;
 }
 
 LayoutUnit RenderMultiColumnFlowThread::initialLogicalWidth() const
 {
     return columnWidth();
 }
 
-void RenderMultiColumnFlowThread::autoGenerateRegionsToBlockOffset(LayoutUnit /*offset*/)
-{
-    // This function ensures we have the correct column set information at all times.
-    // For a simple multi-column layout in continuous media, only one column set child is required.
-    // Once a column is nested inside an enclosing pagination context, the number of column sets
-    // required becomes 2n-1, where n is the total number of nested pagination contexts. For example:
-    //
-    // Column layout with no enclosing pagination model = 2 * 1 - 1 = 1 column set.
-    // Columns inside pages = 2 * 2 - 1 = 3 column sets (bottom of first page, all the subsequent pages, then the last page).
-    // Columns inside columns inside pages = 2 * 3 - 1 = 5 column sets.
-    //
-    // In addition, column spans will force a column set to "split" into before/after sets around the spanning element.
-    //
-    // Finally, we will need to deal with columns inside regions. If regions have variable widths, then there will need
-    // to be unique column sets created inside any region whose width is different from its surrounding regions. This is
-    // actually pretty similar to the spanning case, in that we break up the column sets whenever the width varies.
-    //
-    // FIXME: For now just make one column set. This matches the old multi-column code.
-    // Right now our goal is just feature parity with the old multi-column code so that we can switch over to the
-    // new code as soon as possible.
-    RenderMultiColumnSet* firstSet = toRenderMultiColumnSet(firstRegion());
-    if (firstSet)
-        return;
-
-    invalidateRegions();
-
-    RenderBlockFlow* parentBlock = multiColumnBlockFlow();
-    firstSet = RenderMultiColumnSet::createAnonymous(this);
-    firstSet->setStyle(RenderStyle::createAnonymousStyleWithDisplay(parentBlock->style(), BLOCK));
-    parentBlock->RenderBlock::addChild(firstSet);
-
-    // Even though we aren't placed yet, we can go ahead and set up our size. At this point we're
-    // typically in the middle of laying out the thread, attempting to paginate, and we need to do
-    // some rudimentary "layout" of the set now, so that pagination will work.
-    firstSet->prepareForLayout();
-
-    validateRegions();
-}
-
 void RenderMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
 {
     if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
         multicolSet->recordSpaceShortage(spaceShortage);
 }
 
 void RenderMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
 {
     if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
         multicolSet->updateMinimumColumnHeight(minHeight);
 }
 
+RenderRegion* RenderMultiColumnFlowThread::regionAtBlockOffset(LayoutUnit /*offset*/)
+{
+    // For now there's only one column set, so this is easy:
+    return firstMultiColumnSet();
+}
+
 bool RenderMultiColumnFlowThread::addForcedRegionBreak(LayoutUnit offset, RenderObject* /*breakChild*/, bool /*isBefore*/, LayoutUnit* offsetBreakAdjustment)
 {
     if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset))) {
         multicolSet->addForcedBreak(offset);
         if (offsetBreakAdjustment)
             *offsetBreakAdjustment = pageLogicalHeightForOffset(offset) ? pageRemainingLogicalHeightForOffset(offset, IncludePageBoundary) : LayoutUnit();
         return true;
     }
     return false;
 }
 
 bool RenderMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
-    for (RenderBox* renderer = parentBox()->lastChildBox(); renderer; renderer = renderer->previousSiblingBox()) {
-        if (renderer->isRenderMultiColumnSet())
-            return toRenderMultiColumnSet(renderer)->computedColumnHeight();
-    }
-    // A column set hasn't been created yet. Height may already be known if column-fill is 'auto', though.
-    return !requiresBalancing();
+    if (RenderMultiColumnSet* columnSet = lastMultiColumnSet())
+        return columnSet->computedColumnHeight();
+    return false;
 }
 
 }