Don't split text runs on underline style change

ui/gfx/render_text.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text.h"
 
 #include <algorithm>
 #include <climits>
 
 #include "base/command_line.h"
@@ skipping 394 matching lines @@
 #endif
 }
 
 void RenderText::SetText(const base::string16& text) {
   DCHECK(!composition_range_.IsValid());
   if (text_ == text)
     return;
   text_ = text;
 
   // Adjust ranged styles and colors to accommodate a new text length.
+  // Clear style ranges as they might break new text graphemes and apply
+  // the first style to the whole text instead.
   const size_t text_length = text_.length();
   colors_.SetMax(text_length);
-  for (size_t style = 0; style < NUM_TEXT_STYLES; ++style)
-    styles_[style].SetMax(text_length);
+  for (size_t style = 0; style < NUM_TEXT_STYLES; ++style) {
+    BreakList<bool>& break_list = styles_[style];
+    break_list.SetValue(break_list.breaks().begin()->second);
+    break_list.SetMax(text_length);
+  }
   cached_bounds_and_offset_valid_ = false;
 
   // Reset selection model. SetText should always followed by SetSelectionModel
   // or SetCursorPosition in upper layer.
   SetSelectionModel(SelectionModel());
 
   // Invalidate the cached text direction if it depends on the text contents.
   if (directionality_mode_ == DIRECTIONALITY_FROM_TEXT)
     text_direction_ = base::i18n::UNKNOWN_DIRECTION;
 
@@ skipping 215 matching lines @@
 }
 
 void RenderText::SetStyle(TextStyle style, bool value) {
   styles_[style].SetValue(value);
 
   cached_bounds_and_offset_valid_ = false;
   ResetLayout();
 }
 
 void RenderText::ApplyStyle(TextStyle style, bool value, const Range& range) {
-  styles_[style].ApplyValue(value, range);
+  // Do not change styles mid-grapheme to avoid breaking ligatures.
+  const size_t start = IsValidCursorIndex(range.start()) ? range.start() :
+      IndexOfAdjacentGrapheme(range.start(), CURSOR_BACKWARD);
+  const size_t end = IsValidCursorIndex(range.end()) ? range.end() :
+      IndexOfAdjacentGrapheme(range.end(), CURSOR_FORWARD);
+  styles_[style].ApplyValue(value, Range(start, end));
 
   cached_bounds_and_offset_valid_ = false;
   ResetLayout();
 }
 
 bool RenderText::GetStyle(TextStyle style) const {
   return (styles_[style].breaks().size() == 1) &&
       styles_[style].breaks().front().second;
 }
 
@@ skipping 703 matching lines @@
   SetDisplayOffset(display_offset_.x() + delta_x);
 }
 
 void RenderText::DrawSelection(Canvas* canvas) {
   const std::vector<Rect> sel = GetSubstringBounds(selection());
   for (std::vector<Rect>::const_iterator i = sel.begin(); i < sel.end(); ++i)
     canvas->FillRect(*i, selection_background_focused_color_);
 }
 
 }  // namespace gfx