Improve LayoutMultiColumnFlowThread::IsPageLogicalHeightKnown().

third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.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 345 matching lines @@
 }
 
 bool LayoutMultiColumnFlowThread::NeedsNewWidth() const {
   LayoutUnit new_width;
   unsigned dummy_column_count;  // We only care if used column-width changes.
   CalculateColumnCountAndWidth(new_width, dummy_column_count);
   return new_width != LogicalWidth();
 }
 
 bool LayoutMultiColumnFlowThread::IsPageLogicalHeightKnown() const {
-  if (LayoutMultiColumnSet* column_set = LastMultiColumnSet())
-    return column_set->IsPageLogicalHeightKnown();
-  return false;
+  return all_columns_have_known_height_;
 }
 
 bool LayoutMultiColumnFlowThread::MayHaveNonUniformPageLogicalHeight() const {
   const LayoutMultiColumnSet* column_set = FirstMultiColumnSet();
   if (!column_set)
     return false;
   if (column_set->NextSiblingMultiColumnSet())
     return true;
   return EnclosingFragmentationContext();
 }
@@ skipping 157 matching lines @@
         // new outer row). Without sufficient rows in all ancestor multicol
         // containers, we may use the wrong column height.
         LayoutUnit offset = block_offset_in_enclosing_fragmentation_context_ +
                             first_set->LogicalTopFromMulticolContentEdge();
         enclosing_flow_thread->AppendNewFragmentainerGroupIfNeeded(
             offset, kAssociateWithLatterPage);
       }
     }
   }
 
+  // We'll start by assuming that all columns have some known height, and flip
+  // it to false if we discover that this isn't the case.
+  all_columns_have_known_height_ = true;
+
   for (LayoutBox* column_box = FirstMultiColumnBox(); column_box;
        column_box = column_box->NextSiblingMultiColumnBox()) {
     if (!column_box->IsLayoutMultiColumnSet()) {
       // No other type is expected.
       DCHECK(column_box->IsLayoutMultiColumnSpannerPlaceholder());
       continue;
     }
     LayoutMultiColumnSet* column_set = ToLayoutMultiColumnSet(column_box);
     layout_scope.SetChildNeedsLayout(column_set);
     if (!column_heights_changed_) {
       // This is the initial layout pass. We need to reset the column height,
       // because contents typically have changed.
       column_set->ResetColumnHeight();
     }
+    if (all_columns_have_known_height_ &&
+        !column_set->IsPageLogicalHeightKnown()) {
+      // If any of the column sets requires a layout pass before it has any
+      // clue about its height, we cannot fragment in this pass, just measure
+      // the block sizes.
+      all_columns_have_known_height_ = false;
+    }
     // Since column sets are regular block flow objects, and their position is
     // changed in regular block layout code (with no means for the multicol code
     // to notice unless we add hooks there), store the previous position now. If
     // it changes in the imminent layout pass, we may have to rebalance its
     // columns.
     column_set->StoreOldPosition();
   }
 
   column_heights_changed_ = false;
   InvalidateColumnSets();
@@ skipping 368 matching lines @@
   // and where such out-of-flow objects might be, just go through the whole
   // subtree.
   for (LayoutObject* descendant = layout_object->SlowFirstChild(); descendant;
        descendant = descendant->NextInPreOrder()) {
     if (descendant->IsBox() && descendant->IsOutOfFlowPositioned())
       descendant->ContainingBlock()->InsertPositionedObject(
           ToLayoutBox(descendant));
   }
 }
 
+bool LayoutMultiColumnFlowThread::FinishLayout() {
+  all_columns_have_known_height_ = true;
+  for (const auto* column_set = FirstMultiColumnSet(); column_set;
+       column_set = column_set->NextSiblingMultiColumnSet()) {
+    if (!column_set->IsPageLogicalHeightKnown()) {
+      all_columns_have_known_height_ = false;
+      break;
+    }
+  }
+  return !ColumnHeightsChanged();
+}
+
 // When processing layout objects to remove or when processing layout objects
 // that have just been inserted, certain types of objects should be skipped.
 static bool ShouldSkipInsertedOrRemovedChild(
     LayoutMultiColumnFlowThread* flow_thread,
     const LayoutObject& child) {
   if (child.IsSVGChild()) {
     // Don't descend into SVG objects. What's in there is of no interest, and
     // there might even be a foreignObject there with column-span:all, which
     // doesn't apply to us.
     return true;
@@ skipping 432 matching lines @@
     const {
   return MultiColumnLayoutState(last_set_worked_on_);
 }
 
 void LayoutMultiColumnFlowThread::RestoreMultiColumnLayoutState(
     const MultiColumnLayoutState& state) {
   last_set_worked_on_ = state.ColumnSet();
 }
 
 }  // namespace blink