Implement Pango RenderText for Linux.

ui/gfx/render_text_linux.h

 // 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.
 
 #ifndef UI_GFX_RENDER_TEXT_LINUX_H_
 #define UI_GFX_RENDER_TEXT_LINUX_H_
 #pragma once
 
+#include <pango/pango.h>
+
 #include "ui/gfx/render_text.h"
 
 namespace gfx {
 
 // RenderTextLinux is the Linux implementation of RenderText using Pango.
 class RenderTextLinux : public RenderText {
  public:
   RenderTextLinux();
   virtual ~RenderTextLinux();
 
-private:
+  // Overridden from RenderText:
+  virtual void SetText(const string16& text) OVERRIDE;
+  virtual void SetDisplayRect(const Rect&r) OVERRIDE;
+  virtual void SetCompositionRange(const ui::Range& composition_range) OVERRIDE;
+  virtual void ApplyStyleRange(StyleRange style_range) OVERRIDE;
+  virtual void ApplyDefaultStyle() OVERRIDE;
+  virtual base::i18n::TextDirection GetTextDirection() OVERRIDE;
+  virtual int GetStringWidth() OVERRIDE;
+  virtual void Draw(Canvas* canvas) OVERRIDE;
+  virtual SelectionModel FindCursorPosition(const Point& point) OVERRIDE;
+  virtual Rect GetCursorBounds(const SelectionModel& position,
+                               bool insert_mode) OVERRIDE;
+
+ protected:
+  // Overridden from RenderText:
+  virtual SelectionModel GetLeftSelectionModel(const SelectionModel& current,
+                                               BreakType break_type) OVERRIDE;
+  virtual SelectionModel GetRightSelectionModel(const SelectionModel& current,
+                                                BreakType break_type) OVERRIDE;
+  virtual SelectionModel LeftEndSelectionModel() OVERRIDE;
+  virtual SelectionModel RightEndSelectionModel() OVERRIDE;
+  virtual size_t GetIndexOfPreviousGrapheme(size_t position) OVERRIDE;
+
+ private:
+  enum RelativeLogicalPosition {
+    PREVIOUS,
+    NEXT
+  };
+
+  // Get the logical start index of the next grapheme after |position|.
+  size_t GetIndexOfNextGrapheme(size_t position);
+
+  // Returns the run that contains |position|. Return NULL if not found.
+  GSList* GetRunContainingPosition(size_t position) const;

[behdad_google, 2011/09/06 16:05:03]

Return PangoLayoutRun* instead?

[xji, 2011/09/06 19:54:13]

The comments about the 3 functions using PangoLayoutRun* instead of GSList* make
sense.

But the problems are:
1. the return value of GetRunContainingPosition() is also used to get previous
and next run.
Only GSList carries the links, PangoLayoutLine does not carry the link.

+
+  // Given |utf8_index_of_current_grapheme|, returns the UTF8 or UTF16 index of
+  // next grapheme in the text if |pos| is NEXT, otherwise, returns the index of
+  // previous grapheme. Returns 0 if there is no previous grapheme, and returns
+  // the |text_| length if there is no next grapheme.
+  size_t Utf8IndexOfAdjacentGrapheme(size_t utf8_index_of_current_grapheme,
+                                     RelativeLogicalPosition pos) const;
+  size_t Utf16IndexOfAdjacentGrapheme(size_t utf8_index_of_current_grapheme,
+                                      RelativeLogicalPosition pos) const;
+
+  // Given a |run|, returns the SelectionModel that contains the logical first
+  // or last caret position inside (not at a boundary of) the run.
+  // The returned value represents a cursor/caret position without a selection.
+  SelectionModel FirstSelectionModelInsideRun(const PangoItem* run) const;
+  SelectionModel LastSelectionModelInsideRun(const PangoItem* run) const;
+
+  // Get the selection model visually left or right of |current| by one
+  // grapheme.
+  // The returned value represents a cursor/caret position without a selection.
+  SelectionModel LeftSelectionModel(const SelectionModel& current);
+  SelectionModel RightSelectionModel(const SelectionModel& current);
+
+  // If |layout_| is NULL, create and setup |layout_|, retain and ref
+  // |layout_line_|. Return |layout_|.
+  PangoLayout* EnsureLayout();
+
+  // Unref |layout_| and |pango_line_|. Set them to NULL.
+  void ResetLayout();
+
+  // Setup pango attribute: foreground, background, font, strike.
+  void SetupPangoAttributes(PangoLayout* layout);
+
+  // Append one pango attribute |pango_attr| into pango attribute list |attrs|.
+  void AppendPangoAttribute(size_t start,
+                            size_t end,
+                            PangoAttribute* pango_attr,
+                            PangoAttrList* attrs);
+
+  // Returns |run|'s visually previous run.
+  // The complexity is O(n) since it is a single-linked list.
+  GSList* GetPreviousRun(GSList* run) const;

[behdad_google, 2011/09/06 16:05:03]

So, you search within the current line, right?  I think PangoLayoutRun* both for
input and output is more appropriate.

[xji, 2011/09/06 19:54:13]

input can not be PangoLayoutLine since it does not carry links.

So, to keep it consistent, I still keep the output as GSList .

+
+  // Returns the last run in |layout_line_|.
+  // The complexity is O(n) since it is a single-linked list.
+  GSList* GetLastRun() const;

[behdad_google, 2011/09/06 16:05:03]

Same here.  And in any other place a single run is referenced.

[xji, 2011/09/06 19:54:13]

This could be changed to PangoLayoutLine*.
I have not changed it yet to keep it consistent with the other functions
returning GSList.
If you think it is better to use PangoLayoutLine, I will change.

+
+  size_t Utf16IndexToUtf8Index(size_t index) const;
+  size_t Utf8IndexToUtf16Index(size_t index) const;
+
+  PangoLayout* layout_;
+
+  PangoLayoutLine* layout_line_;

[behdad_google, 2011/09/06 16:05:03]

Something like current_line_ may be more appropriate.  Humm, or do we only care
about single-line paragraphs?  If that's the case, maybe call
pango_layout_set_single_paragraph_mode() too.

[xji, 2011/09/06 19:54:13]

Done.
It is single line mode.
Does pango_layout_set_single_paragraph_mode() save performance as well?

+
   DISALLOW_COPY_AND_ASSIGN(RenderTextLinux);
 };
 
 }  // namespace gfx;
 
 #endif  // UI_GFX_RENDER_TEXT_LINUX_H_