Fix textarea font autosizing oscillation when the number of lines exceeds 4. The proposed fix is no…

Source/core/rendering/TextAutosizer.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 346 matching lines @@
     // the same amount even if they're different widths; so do hasColumns()
     // containers, and probably flexboxes...
 }
 
 bool TextAutosizer::isAutosizingCluster(const RenderBlock* renderer, TextAutosizingClusterInfo& parentClusterInfo)
 {
     ASSERT(isAutosizingContainer(renderer));
 
     return isNarrowDescendant(renderer, parentClusterInfo)
         || isWiderDescendant(renderer, parentClusterInfo)
-        || isIndependentDescendant(renderer);
+        || isIndependentDescendant(renderer)
+        || containerIsTextArea(renderer);

[johnme, 2013/04/29 11:11:26]

Please add this as a condition in isIndependentDescendant instead of here. This
is just a convenience method; isIndependentDescendant has all the logic for
determining what is a cluster, except for the width-based checks which are done
in the other two methods.

[timvolodine, 2013/04/29 17:59:13]

Done.

 }
 
 bool TextAutosizer::containerShouldBeAutosized(const RenderBlock* container)
 {
     if (containerContainsOneOfTags(container, formInputTags()))
         return false;
 
     if (containerIsRowOfLinks(container))
         return false;
 
@@ skipping 53 matching lines @@
             linkCount++;
             // Skip traversing descendants of the link.
             renderer = renderer->nextInPreOrderAfterChildren(container);
         } else
             renderer = nextInPreOrderSkippingDescendantsOfContainers(renderer, container);
     }
 
     return (linkCount >= 3);
 }
 
+bool TextAutosizer::containerIsTextArea(const RenderBlock* container)

[johnme, 2013/04/29 11:11:26]

Nit: This method is so simple, that you might as well just inline it in the two
places it gets used.

[timvolodine, 2013/04/29 17:59:13]

Done.

+{
+    return container->isTextArea();
+}
+
 bool TextAutosizer::contentHeightIsConstrained(const RenderBlock* container)
 {
     // FIXME: Propagate constrainedness down the tree, to avoid inefficiently walking back up from each box.
     // FIXME: This code needs to take into account vertical writing modes.
     // FIXME: Consider additional heuristics, such as ignoring fixed heights if the content is already overflowing before autosizing kicks in.
     for (; container; container = container->containingBlock()) {
         RenderStyle* style = container->style();
         if (style->overflowY() >= OSCROLL)
             return false;
         if (style->height().isSpecified() || style->maxHeight().isSpecified()) {
@@ skipping 18 matching lines @@
     // Don't autosize clusters that contain less than 4 lines of text (in
     // practice less lines are required, since measureDescendantTextWidth
     // assumes that characters are 1em wide, but most characters are narrower
     // than that, so we're overestimating their contribution to the linecount).
     //
     // This is to reduce the likelihood of autosizing things like headers and
     // footers, which can be quite visually distracting. The rationale is that
     // if a cluster contains very few lines of text then it's ok to have to zoom
     // in and pan from side to side to read each line, since if there are very
     // few lines of text you'll only need to pan across once or twice.
+    //
+    // An exception to the 4 lines of text are the textarea clusters, which are
+    // always autosized by default (i.e. threated as if they contain more than 4
+    // lines of text). This is to ensure that the text does not suddenly gets

[johnme, 2013/04/29 11:11:26]

Nit: s/gets/get/

[timvolodine, 2013/04/29 17:59:13]

Done.

+    // autosized when the user enters more than 4 lines of text.
     float totalTextWidth = 0;
     const float minLinesOfText = 4;
     float minTextWidth = blockWidth * minLinesOfText;
     for (size_t i = 0; i < clusterInfos.size(); ++i) {
         measureDescendantTextWidth(clusterInfos[i].blockContainingAllText, clusterInfos[i], minTextWidth, totalTextWidth);
         if (totalTextWidth >= minTextWidth)
             return true;
+        if (containerIsTextArea(clusterInfos[i].root))

[johnme, 2013/04/29 11:11:26]

Nit: would be nice to move this check to the start of the for loop, so that when
it is a textarea we early-out rather than doing the expensive call to
measureDescendantTextWidth.

[timvolodine, 2013/04/29 17:59:13]

Done.

+            return true;
     }
     return false;
 }
 
 void TextAutosizer::measureDescendantTextWidth(const RenderBlock* container, TextAutosizingClusterInfo& clusterInfo, float minTextWidth, float& textWidth)
 {
     bool skipLocalText = !containerShouldBeAutosized(container);
 
     RenderObject* descendant = nextInPreOrderSkippingDescendantsOfContainers(container, container);
     while (descendant) {
@@ skipping 110 matching lines @@
         if (i + 1 < clusterInfos.size()) {
             float currentWidth = clusterInfos[i].root->contentLogicalWidth();
             float nextWidth = clusterInfos[i + 1].root->contentLogicalWidth();
             if (currentWidth - nextWidth > maxWidthDifferenceWithinGroup)
                 groups.grow(groups.size() + 1);
         }
     }
 }
 
 } // namespace WebCore