Implement Pango RenderText for Linux.

ui/gfx/render_text_linux.cc

 // Copyright (c) 2011 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_linux.h"
 
+#include <pango/pangocairo.h>
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "ui/gfx/canvas_skia.h"
+#include "ui/gfx/pango_util.h"
+#include "unicode/uchar.h"
+#include "unicode/ustring.h"
+
+namespace {
+
+// TODO(xji): instead of converting each R or G or B from 8-bit to 16-bit,
+// it should also massage A in the conversion.
+int ConvertColorFrom8BitTo16Bit(int c) {
+  return (c << 8) + c;
+}
+
+}  // namespace
+
+// TODO(xji): index saved in upper layer is utf16 index. Pango uses utf8 index.
+// Since caret_pos is used internally, we could save utf8 index for caret_pos
+// to avoid conversion.
+
 namespace gfx {
 
 RenderTextLinux::RenderTextLinux()
-    : RenderText() {
+    : layout_(NULL),
+      layout_line_(NULL) {
 }
 
 RenderTextLinux::~RenderTextLinux() {
+  ResetLayout();
 }
 
 RenderText* RenderText::CreateRenderText() {
   return new RenderTextLinux;
 }
 
+void RenderTextLinux::SetText(const string16& text) {
+  RenderText::SetText(text);
+  ResetLayout();
+}
+
+void RenderTextLinux::SetDisplayRect(const Rect&r) {
+  RenderText::SetDisplayRect(r);
+  ResetLayout();
+}
+
+void RenderTextLinux::SetCompositionRange(const ui::Range& composition_range) {
+  RenderText::SetCompositionRange(composition_range);
+  ResetLayout();
+}
+
+void RenderTextLinux::ApplyStyleRange(StyleRange style_range) {
+  RenderText::ApplyStyleRange(style_range);
+  ResetLayout();
+}
+
+void RenderTextLinux::ApplyDefaultStyle() {
+  RenderText::ApplyDefaultStyle();
+  ResetLayout();
+}
+
+base::i18n::TextDirection RenderTextLinux::GetTextDirection() {
+  EnsureLayout();
+
+  const char* layout_text = pango_layout_get_text(layout_);
+  PangoDirection base_dir = pango_find_base_dir(layout_text, -1);
+  if (base_dir == PANGO_DIRECTION_RTL || base_dir == PANGO_DIRECTION_WEAK_RTL)
+    return base::i18n::RIGHT_TO_LEFT;
+  return base::i18n::LEFT_TO_RIGHT;
+}
+
+int RenderTextLinux::GetStringWidth() {
+  PangoLayout* layout = EnsureLayout();
+  int width;
+  pango_layout_get_pixel_size(layout, &width, NULL);
+  return width;
+}
+
+void RenderTextLinux::Draw(Canvas* canvas) {
+  PangoLayout* layout = EnsureLayout();
+  Rect bounds(display_rect());
+
+  // Clip the canvas to the text display area.
+  CanvasSkia* canvas_skia = canvas->AsCanvasSkia();
+  canvas_skia->ClipRectInt(
+      bounds.x(), bounds.y(), bounds.width(), bounds.height());
+
+  skia::ScopedPlatformPaint scoped_platform_paint(canvas_skia);
+  cairo_t* cr = scoped_platform_paint.GetPlatformSurface();
+  cairo_save(cr);
+  cairo_rectangle(cr, bounds.x(), bounds.y(), bounds.width(), bounds.height());
+  cairo_clip(cr);
+
+  int text_width, text_height;
+  pango_layout_get_pixel_size(layout, &text_width, &text_height);
+  Point offset(ToViewPoint(Point()));
+  // Vertically centered.
+  int text_y = offset.y() + ((bounds.height() - text_height) / 2);
+  // TODO(xji): need to use SkCanvas->drawPosText() for gpu acceleration.
+  cairo_move_to(cr, offset.x(), text_y);
+  pango_cairo_show_layout(cr, layout);
+
+  cairo_restore(cr);
+
+  // Paint cursor.
+  bounds = GetUpdatedCursorBounds();
+  if (cursor_visible() && focused())
+      canvas->DrawRectInt(kCursorColor,
+                          bounds.x(),
+                          bounds.y(),
+                          bounds.width(),
+                          bounds.height());
+}
+
+SelectionModel RenderTextLinux::FindCursorPosition(const Point& point) {
+  // TODO(xji): when points outside of text, return HOME/END position.
+  PangoLayout* layout = EnsureLayout();
+
+  if (text().empty())
+    return SelectionModel(0, 0, SelectionModel::LEADING);
+
+  Point p(ToTextPoint(point));
+  int caret_pos, trailing;
+  pango_layout_xy_to_index(layout, p.x() * PANGO_SCALE, p.y() * PANGO_SCALE,
+                           &caret_pos, &trailing);
+
+  size_t selection_end = caret_pos;
+  if (trailing > 0) {
+    const char* pango_text = pango_layout_get_text(layout);
+    const char* ch = g_utf8_offset_to_pointer(pango_text + caret_pos, trailing);
+    DCHECK_GE(ch, pango_text);
+    DCHECK_LE(ch, pango_text + strlen(pango_text));
+    selection_end = ch - pango_text;
+  }
+
+  return SelectionModel(
+      Utf8IndexToUtf16Index(selection_end),
+      Utf8IndexToUtf16Index(caret_pos),
+      trailing > 0 ? SelectionModel::TRAILING : SelectionModel::LEADING);
+}
+
+Rect RenderTextLinux::GetCursorBounds(const SelectionModel& selection,
+                                      bool insert_mode) {
+  PangoLayout* layout = EnsureLayout();
+
+  size_t caret_pos = insert_mode ? selection.caret_pos() :
+                                   selection.selection_end();
+  PangoRectangle pos;
+  pango_layout_index_to_pos(layout, Utf16IndexToUtf8Index(caret_pos), &pos);
+
+  SelectionModel::CaretPlacement caret_placement = selection.caret_placement();
+  int x = pos.x;
+  if ((insert_mode && caret_placement == SelectionModel::TRAILING) ||
+      (!insert_mode && pos.width < 0))
+    x += pos.width;
+  x = PANGO_PIXELS(x);
+
+  int h = std::min(display_rect().height(), PANGO_PIXELS(pos.height));
+  Rect bounds(x, (display_rect().height() - h) / 2, 0, h);
+  bounds.set_origin(ToViewPoint(bounds.origin()));
+
+  if (!insert_mode)
+    bounds.set_width(std::abs(pos.width));
+
+  return bounds;
+}
+
+SelectionModel RenderTextLinux::GetLeftSelectionModel(
+    const SelectionModel& current,
+    BreakType break_type) {
+  EnsureLayout();
+
+  if (break_type == LINE_BREAK || text().empty())
+    return LeftEndSelectionModel();
+  if (break_type == CHARACTER_BREAK)
+    return LeftSelectionModel(current);
+  // TODO(xji): not implemented yet.
+  return RenderText::GetLeftSelectionModel(current, break_type);
+}
+
+SelectionModel RenderTextLinux::GetRightSelectionModel(
+    const SelectionModel& current,
+    BreakType break_type) {
+  EnsureLayout();
+
+  if (break_type == LINE_BREAK || text().empty())
+    return RightEndSelectionModel();
+  if (break_type == CHARACTER_BREAK)
+    return RightSelectionModel(current);
+  // TODO(xji): not implemented yet.
+  return RenderText::GetRightSelectionModel(current, break_type);
+}
+
+SelectionModel RenderTextLinux::LeftEndSelectionModel() {
+  if (GetTextDirection() == base::i18n::RIGHT_TO_LEFT) {
+    if (layout_line_->runs) {
+      PangoLayoutRun* first_visual_run =
+          reinterpret_cast<PangoLayoutRun*>(layout_line_->runs->data);
+      PangoItem* item = first_visual_run->item;
+      if (item->analysis.level % 2 == 0) {  // LTR.
+        size_t caret = Utf8IndexToUtf16Index(item->offset);
+        return SelectionModel(text().length(), caret, SelectionModel::LEADING);
+      } else {  // RTL.
+        size_t caret = Utf16IndexOfAdjacentGrapheme(item->offset + item->length,
+                                                    PREVIOUS);
+        return SelectionModel(text().length(), caret, SelectionModel::TRAILING);
+      }
+    }
+  }
+  return SelectionModel(0, 0, SelectionModel::LEADING);
+}
+
+SelectionModel RenderTextLinux::RightEndSelectionModel() {
+  if (GetTextDirection() == base::i18n::LEFT_TO_RIGHT) {
+    GSList* last_visual_run = GetLastRun();
+    if (last_visual_run) {
+      PangoItem* item =
+          reinterpret_cast<PangoLayoutRun*>(last_visual_run->data)->item;
+      if (item->analysis.level % 2 == 0) {  // LTR.
+        size_t caret = Utf16IndexOfAdjacentGrapheme(item->offset + item->length,
+                                                    PREVIOUS);
+        return SelectionModel(text().length(), caret, SelectionModel::TRAILING);
+      } else {  // RTL.
+        size_t caret = Utf8IndexToUtf16Index(item->offset);
+        return SelectionModel(text().length(), caret, SelectionModel::LEADING);
+      }
+    }
+  }
+  return SelectionModel(0, 0, SelectionModel::LEADING);
+}
+
+size_t RenderTextLinux::GetIndexOfPreviousGrapheme(size_t position) {
+  EnsureLayout();
+  size_t index = Utf16IndexToUtf8Index(position);
+  return Utf16IndexOfAdjacentGrapheme(index, PREVIOUS);
+}
+
+size_t RenderTextLinux::GetIndexOfNextGrapheme(size_t position) {
+  EnsureLayout();
+  size_t index = Utf16IndexToUtf8Index(position);
+  return Utf16IndexOfAdjacentGrapheme(index, NEXT);
+}
+
+GSList* RenderTextLinux::GetRunContainingPosition(size_t position) const {
+  GSList* run = layout_line_->runs;
+  while (run) {
+    PangoItem* box = reinterpret_cast<PangoLayoutRun*>(run->data)->item;
+    size_t run_start = Utf8IndexToUtf16Index(box->offset);
+    size_t run_end = Utf8IndexToUtf16Index(box->offset + box->length);
+
+    if (position >= run_start && position < run_end)
+      return run;
+    run = run->next;
+  }
+  return NULL;
+}
+
+size_t RenderTextLinux::Utf8IndexOfAdjacentGrapheme(
+    size_t utf8_index_of_current_grapheme,
+    RelativeLogicalPosition pos) const {
+  PangoLogAttr* log_attrs;
+  gint n_attrs;
+  pango_layout_get_log_attrs(layout_, &log_attrs, &n_attrs);
+
+  const char* layout_text = pango_layout_get_text(layout_);
+  const char* ch = layout_text + utf8_index_of_current_grapheme;
+  int char_offset = static_cast<int>(g_utf8_pointer_to_offset(layout_text, ch));
+
+  if (pos == PREVIOUS) {
+    if (ch > layout_text) {
+      do {
+        ch = g_utf8_find_prev_char(layout_text, ch);
+        --char_offset;
+      } while (ch && *ch && !log_attrs[char_offset].is_cursor_position);

[behdad_google, 2011/09/06 21:57:17]

I would change this while condition to:

while (layout_text < ch && !log_attrs[char_offset].is_cursor_position);

[xji, 2011/09/07 17:14:36]

Done.

+      if (!ch)
+        ch = layout_text;

[behdad_google, 2011/09/06 21:57:17]

Then you shouldn't need this.

[xji, 2011/09/07 17:14:36]

Done.

+    }
+  } else {
+    if (ch < layout_text + strlen(layout_text)) {
+      do {
+        ch = g_utf8_find_next_char(ch, NULL);
+        ++char_offset;
+      } while (ch && *ch && !log_attrs[char_offset].is_cursor_position);

[behdad_google, 2011/09/06 21:57:17]

I would then do this one as:

while (ch < layout_text + text_len &&
!log_attrs[char_offset].is_cursor_position);

[xji, 2011/09/07 17:14:36]

Done.

+      if (!ch || ch >= layout_text + strlen(layout_text))
+        ch = layout_text + strlen(layout_text);

[behdad_google, 2011/09/06 21:57:17]

You do three strlen()s in this block alone!  Save the length and reuse please.

[xji, 2011/09/07 17:14:36]

Done.

+    }
+  }
+
+  size_t utf8_index = static_cast<size_t>(ch - layout_text);

[behdad_google, 2011/09/06 21:57:17]

So, you maintain both ch and char_offset.  You can simplify the code by not
tracking ch in the while loops, and do a single g_utf8_offset_to_pointer() at
the end to move ch to the correct position.

[xji, 2011/09/07 17:14:36]

This function is re-written by only use char_offset in the loop.

+  g_free(log_attrs);

[behdad_google, 2011/09/06 21:57:17]

Ok, this is no good.  Please save log_attrs in the controller.  While there,
perhaps simply save layout_text and layout_text_len too.  Since you have
EnsureLayout() and ResetLayout(), keeping those updated is supereasy.

[xji, 2011/09/07 17:14:36]

Done.

+  return utf8_index;
+}
+
+size_t RenderTextLinux::Utf16IndexOfAdjacentGrapheme(
+    size_t utf8_index_of_current_grapheme,
+    RelativeLogicalPosition pos) const {
+  size_t utf8_index = Utf8IndexOfAdjacentGrapheme(
+      utf8_index_of_current_grapheme, pos);
+  return Utf8IndexToUtf16Index(utf8_index);
+}
+
+SelectionModel RenderTextLinux::FirstSelectionModelInsideRun(
+    const PangoItem* run) const {
+  size_t caret = Utf8IndexToUtf16Index(run->offset);
+  size_t cursor = Utf16IndexOfAdjacentGrapheme(run->offset, NEXT);
+  return SelectionModel(cursor, caret, SelectionModel::TRAILING);
+}
+
+SelectionModel RenderTextLinux::LastSelectionModelInsideRun(
+    const PangoItem* run) const {

[behdad_google, 2011/09/06 21:57:17]

Would be easier to call PangoItem instances item instead of run, to
differentiate between PangoLayoutRun and PangoItem.  Alternatively, just make
the API get PangoLayoutRun and use run->item instead.

[xji, 2011/09/07 17:14:36]

Done.

+  size_t caret = Utf16IndexOfAdjacentGrapheme(run->offset + run->length,
+                                              PREVIOUS);
+  return SelectionModel(caret, caret, SelectionModel::LEADING);
+}
+
+// Assume caret_pos in |current| is n, 'l' represents leading in
+// caret_placement and 't' represents trailing in caret_placement. Following
+// is the calculation from (caret_pos, caret_placement) in |current| to
+// (selection_end, caret_pos, caret_placement) when moving cursor left by
+// one grapheme (for simplicity, assume each grapheme is one character).
+// If n is in LTR run,
+// (n, t) ---> (n, n, l).
+// (n, l) ---> (n-1, n-1, l) if n is inside run (not at boundary).
+// (n, l) ---> goto across run case if n is at run boundary.
+// If n is in RTL run,
+// (n, l) --> (n+1, n, t).
+// (n, t) --> (n+2, n+1, t) if n is inside run.
+// (n, t) --> goto across run case if n is at run boundary.
+// If n is at run boundary, get its visually left run,
+// If left run is LTR run,
+// (n, t) --> (left run's end, left run's end, l).
+// If left run is RTL run,
+// (n, t) --> (left run's begin + 1, left run's begin, t).
+SelectionModel RenderTextLinux::LeftSelectionModel(

[behdad_google, 2011/09/06 21:57:17]

I need much more time to review this one for correctness, so that has to wait
till tomorrow morning.

+    const SelectionModel& selection) {
+  size_t caret = selection.caret_pos();
+  SelectionModel::CaretPlacement caret_placement = selection.caret_placement();
+  GSList* run = GetRunContainingPosition(caret);
+  DCHECK(run);
+
+  PangoItem* box = reinterpret_cast<PangoLayoutRun*>(run->data)->item;
+  size_t run_start = Utf8IndexToUtf16Index(box->offset);
+  size_t run_end = Utf8IndexToUtf16Index(box->offset + box->length);
+
+  if (box->analysis.level % 2 == 0) {  // LTR run.
+    if (caret_placement == SelectionModel::TRAILING)
+      return SelectionModel(caret, caret, SelectionModel::LEADING);
+    else if (caret > run_start) {
+      caret = GetIndexOfPreviousGrapheme(caret);
+      return SelectionModel(caret, caret, SelectionModel::LEADING);
+    }
+  } else {  // RTL run.
+    if (caret_placement == SelectionModel::LEADING) {
+      size_t cursor = GetIndexOfNextGrapheme(caret);
+      return SelectionModel(cursor, caret, SelectionModel::TRAILING);
+    } else if (selection.selection_end() < run_end) {
+      caret = GetIndexOfNextGrapheme(caret);
+      size_t cursor = GetIndexOfNextGrapheme(caret);
+      return SelectionModel(cursor, caret, SelectionModel::TRAILING);
+    }
+  }
+
+  // The character is at the begin of its run; advance to the previous visual
+  // run.
+  GSList* prev_run = GetPreviousRun(run);
+  if (!prev_run)
+    return LeftEndSelectionModel();
+
+  box = reinterpret_cast<PangoLayoutRun*>(prev_run->data)->item;
+  return (box->analysis.level % 2) ? FirstSelectionModelInsideRun(box) :
+                                     LastSelectionModelInsideRun(box);
+}
+
+// Assume caret_pos in |current| is n, 'l' represents leading in
+// caret_placement and 't' represents trailing in caret_placement. Following
+// is the calculation from (caret_pos, caret_placement) in |current| to
+// (selection_end, caret_pos, caret_placement) when moving cursor right by
+// one grapheme (for simplicity, assume each grapheme is one character).
+// If n is in LTR run,
+// (n, l) ---> (n+1, n, t).
+// (n, t) ---> (n+2, n+1, t) if n is inside run (not at boundary).
+// (n, t) ---> goto across run case if n is at run boundary.
+// If n is in RTL run,
+// (n, t) --> (n, n, l).
+// (n, l) --> (n-1, n-1, l) if n is inside run.
+// (n, l) --> goto across run case if n is at run boundary.
+// If n is at run boundary, get its visually right run,
+// If right run is LTR run,
+// (n, t) --> (right run's begin + 1, right run's begin, t).
+// If right run is RTL run,
+// (n, t) --> (right run's end, right run's end, l).
+SelectionModel RenderTextLinux::RightSelectionModel(
+    const SelectionModel& selection) {
+  size_t caret = selection.caret_pos();
+  SelectionModel::CaretPlacement caret_placement = selection.caret_placement();
+  GSList* run = GetRunContainingPosition(caret);
+  DCHECK(run);
+
+  PangoItem* box = reinterpret_cast<PangoLayoutRun*>(run->data)->item;
+  size_t run_start = Utf8IndexToUtf16Index(box->offset);
+  size_t run_end = Utf8IndexToUtf16Index(box->offset + box->length);
+
+  if (box->analysis.level % 2 == 0) {  // LTR run.
+    if (caret_placement == SelectionModel::LEADING) {
+      size_t cursor = GetIndexOfNextGrapheme(caret);
+      return SelectionModel(cursor, caret, SelectionModel::TRAILING);
+    } else if (selection.selection_end() < run_end) {
+      caret = GetIndexOfNextGrapheme(caret);
+      size_t cursor = GetIndexOfNextGrapheme(caret);
+      return SelectionModel(cursor, caret, SelectionModel::TRAILING);
+    }
+  } else {  // RTL run.
+    if (caret_placement == SelectionModel::TRAILING)
+      return SelectionModel(caret, caret, SelectionModel::LEADING);
+    else if (caret > run_start) {
+      caret = GetIndexOfPreviousGrapheme(caret);
+      return SelectionModel(caret, caret, SelectionModel::LEADING);
+    }
+  }
+
+  // The character is at the end of its run; advance to the next visual run.
+  GSList* next_run = run->next;
+  if (!next_run)
+    return RightEndSelectionModel();
+
+  box = reinterpret_cast<PangoLayoutRun*>(next_run->data)->item;
+  return (box->analysis.level % 2) ? LastSelectionModelInsideRun(box) :
+                                     FirstSelectionModelInsideRun(box);
+}
+
+PangoLayout* RenderTextLinux::EnsureLayout() {
+  if (layout_ == NULL) {
+    CanvasSkia canvas(display_rect().width(), display_rect().height(), false);
+    skia::ScopedPlatformPaint scoped_platform_paint(&canvas);
+    cairo_t* cr = scoped_platform_paint.GetPlatformSurface();
+
+    layout_ = pango_cairo_create_layout(cr);
+    SetupPangoLayout(
+        layout_,
+        text(),
+        default_style().font,
+        display_rect().width(),
+        base::i18n::GetFirstStrongCharacterDirection(text()),
+        CanvasSkia::DefaultCanvasTextAlignment());
+
+    // No width set so that the x-axis position is relative to the start of the
+    // text. ToViewPoint and ToTextPoint take care of the position conversion
+    // between text space and view spaces.
+    pango_layout_set_width(layout_, -1);
+    pango_layout_set_height(layout_, display_rect().height() * PANGO_SCALE);
+    SetupPangoAttributes(layout_);
+
+    layout_line_ = pango_layout_get_line_readonly(layout_, 0);
+    pango_layout_line_ref(layout_line_);
+  }
+  return layout_;
+}
+
+void RenderTextLinux::ResetLayout() {
+  // set_cached_bounds_and_offset_valid(false) is done in RenderText for every
+  // operation that triggers ResetLayout().
+  if (layout_) {
+    g_object_unref(layout_);
+    layout_ = NULL;
+  }
+  if (layout_line_) {
+    pango_layout_line_unref(layout_line_);
+    layout_line_ = NULL;
+  }
+}
+
+void RenderTextLinux::SetupPangoAttributes(PangoLayout* layout) {
+  PangoAttrList* attrs = pango_attr_list_new();
+  // Set selection background color.
+  SkColor selection_color =
+      focused() ? kFocusedSelectionColor : kUnfocusedSelectionColor;
+  size_t start = std::min(MinOfSelection(), text().length());
+  size_t end = std::min(MaxOfSelection(), text().length());
+  PangoAttribute* pango_attr;
+  if (end > start) {
+    pango_attr = pango_attr_background_new(
+        ConvertColorFrom8BitTo16Bit(SkColorGetR(selection_color)),
+        ConvertColorFrom8BitTo16Bit(SkColorGetG(selection_color)),
+        ConvertColorFrom8BitTo16Bit(SkColorGetB(selection_color)));
+    AppendPangoAttribute(start, end, pango_attr, attrs);
+  }
+
+  StyleRanges ranges_of_style(style_ranges());
+  ApplyCompositionAndSelectionStyles(&ranges_of_style);
+
+  for (StyleRanges::const_iterator i = ranges_of_style.begin();
+       i < ranges_of_style.end(); ++i) {
+    start = std::min(i->range.start(), text().length());
+    end = std::min(i->range.end(), text().length());
+    if (start >= end)
+      continue;
+
+    const Font& font = !i->underline ? i->font :
+        i->font.DeriveFont(0, i->font.GetStyle() | Font::UNDERLINED);
+    PangoFontDescription* desc = font.GetNativeFont();
+    pango_attr = pango_attr_font_desc_new(desc);
+    AppendPangoAttribute(start, end, pango_attr, attrs);
+    pango_font_description_free(desc);
+
+    SkColor foreground = i->foreground;
+    pango_attr = pango_attr_foreground_new(
+        ConvertColorFrom8BitTo16Bit(SkColorGetR(foreground)),
+        ConvertColorFrom8BitTo16Bit(SkColorGetG(foreground)),
+        ConvertColorFrom8BitTo16Bit(SkColorGetB(foreground)));
+    AppendPangoAttribute(start, end, pango_attr, attrs);
+
+    if (i->strike) {
+      pango_attr = pango_attr_strikethrough_new(true);
+      AppendPangoAttribute(start, end, pango_attr, attrs);
+    }
+  }
+
+  pango_layout_set_attributes(layout, attrs);
+  pango_attr_list_unref(attrs);
+}
+
+void RenderTextLinux::AppendPangoAttribute(size_t start,
+                                           size_t end,
+                                           PangoAttribute* pango_attr,
+                                           PangoAttrList* attrs) {
+  pango_attr->start_index = Utf16IndexToUtf8Index(start);
+  pango_attr->end_index = Utf16IndexToUtf8Index(end);
+  pango_attr_list_insert(attrs, pango_attr);
+}
+
+GSList* RenderTextLinux::GetPreviousRun(GSList* run) const {
+  GSList* current = layout_line_->runs;
+  GSList* prev = NULL;
+  while (current) {
+    if (current == run)
+      return prev;
+    prev = current;
+    current = current->next;
+  }
+  return NULL;
+}
+
+GSList* RenderTextLinux::GetLastRun() const {
+  GSList* current = layout_line_->runs;
+  while (current && current->next) {
+    current = current->next;
+  }
+  return current;
+}
+
+size_t RenderTextLinux::Utf16IndexToUtf8Index(size_t index) const {
+  int32_t utf8_index = 0;
+  UErrorCode ec = U_ZERO_ERROR;
+  u_strToUTF8(NULL, 0, &utf8_index, text().data(), index, &ec);
+  // Even given a destination buffer as NULL and destination capacity as 0,
+  // if the output length is equal to or greater than the capacity, then the
+  // UErrorCode is set to U_STRING_NOT_TERMINATED_WARNING or
+  // U_BUFFER_OVERFLOW_ERROR respectively.
+  // Please refer to
+  // http://userguide.icu-project.org/strings#TOC-Using-C-Strings:-NUL-Terminated-vs
+  // for detail (search for "Note that" below "Preflighting").
+  DCHECK(ec == U_BUFFER_OVERFLOW_ERROR ||
+         ec == U_STRING_NOT_TERMINATED_WARNING);
+  return utf8_index;
+}
+
+size_t RenderTextLinux::Utf8IndexToUtf16Index(size_t index) const {
+  int32_t utf16_index = 0;
+  UErrorCode ec = U_ZERO_ERROR;
+  const char* layout_text = pango_layout_get_text(layout_);
+  u_strFromUTF8(NULL, 0, &utf16_index, layout_text, index, &ec);
+  DCHECK(ec == U_BUFFER_OVERFLOW_ERROR ||
+         ec == U_STRING_NOT_TERMINATED_WARNING);
+  return utf16_index;
+}
+
 }  // namespace gfx