Separate selection highlight from pango layout

ui/gfx/render_text.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_H_
 #define UI_GFX_RENDER_TEXT_H_
 #pragma once
 
 #include <algorithm>
 #include <vector>
@@ skipping 191 matching lines @@
   virtual SelectionModel GetLeftSelectionModel(const SelectionModel& current,
                                                BreakType break_type);
   virtual SelectionModel GetRightSelectionModel(const SelectionModel& current,
                                                 BreakType break_type);
 
   // Get the SelectionModels corresponding to visual text ends.
   // The returned value represents a cursor/caret position without a selection.
   virtual SelectionModel LeftEndSelectionModel();
   virtual SelectionModel RightEndSelectionModel();
 
-  // Get the logical index of the grapheme preceeding the argument |position|.
-  virtual size_t GetIndexOfPreviousGrapheme(size_t position);
-
   // Get the visual bounds containing the logical substring within |from| to
   // |to|. These bounds could be visually discontinuous if the substring is
   // split by a LTR/RTL level change. These bounds are in local coordinates, but
   // may be outside the visible region if the text is longer than the textfield.
   // Subsequent text, cursor, or bounds changes may invalidate returned values.
-  // TODO(msw) Re-evaluate this function's necessity and signature.
   virtual std::vector<Rect> GetSubstringBounds(size_t from, size_t to);

[Alexei Svitkine (slow), 2011/11/28 19:56:14]

Maybe change the signature of this to:

virtual void GetSubstringBounds(size_t from,
                                size_t to,
                                std::vector<Rect>* bounds);

Given that RenderTextLinux's version already wraps a function with that
signature and that returning a vector by value involves inefficient copying.

[xji, 2011/11/29 01:37:02]

Changed.
It is generally true that changing the signature as above saves vector copying.
But in RenderTextLinux, since I cached the selection bounds (to avoid
unnecessary g_free), there is still vector copying involved if the (from, to) is
the selection range, unless I change the signature to:

virtual std::vector<Rect>* GetSubstringBounds(size_t from, size_t to,
std::vector<Rect>* bounds)

so that when (from, to) is the same as logical selection, return
&selection_virtual_bounds_, and leave |bounds| untouched. The problem is that
this API will have different behavior in Linux and Win.

So I keep the API as what you suggested with extra vector copying in Linux.

 
+  // Sets the selection model, the argument is assumed to be valid.
+  virtual void SetSelectionModel(const SelectionModel& selection_model);
+
   // Return true if cursor can appear in front of the character at |position|,
   // which means it is a grapheme boundary or the first character in the text.
   virtual bool IsCursorablePosition(size_t position) = 0;
 
   // Updates the layout so that the next draw request can correctly
   // render the text and its attributes.
   virtual void UpdateLayout() = 0;
 
+  // Draw the text.
+  virtual void DrawVisualText(Canvas* canvas) = 0;
+
+  // Get the logical index of the grapheme preceding the argument |position|.
+  size_t GetIndexOfPreviousGrapheme(size_t position);
+
   // Apply composition style (underline) to composition range and selection
   // style (foreground) to selection range.
   void ApplyCompositionAndSelectionStyles(StyleRanges* style_ranges) const;
 
   // Convert points from the text space to the view space and back.
   // Handles the display area, display offset, and the application LTR/RTL mode.
   Point ToTextPoint(const Point& point);
   Point ToViewPoint(const Point& point);
 
  private:
   friend class RenderTextTest;
 
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, DefaultStyle);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, CustomDefaultStyle);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, ApplyStyleRange);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, StyleRangesAdjust);
 
   // Return an index belonging to the |next| or previous logical grapheme.
   // The return value is bounded by 0 and the text length, inclusive.
   virtual size_t IndexOfAdjacentGrapheme(size_t index, bool next) = 0;
 
-  // Sets the selection model, the argument is assumed to be valid.
-  void SetSelectionModel(const SelectionModel& selection_model);
-
   // Set the cursor to |position|, with the caret trailing the previous
   // grapheme, or if there is no previous grapheme, leading the cursor position.
   // If |select| is false, the selection start is moved to the same position.
   // If the |position| is not a cursorable position (not on grapheme boundary),
   // it is a NO-OP.
   void MoveCursorTo(size_t position, bool select);
 
   // Update the cached bounds and display offset to ensure that the current
   // cursor is within the visible display area.
   void UpdateCachedBoundsAndOffset();
 
+  // Draw the selection and cursor.
+  void DrawSelection(Canvas* canvas);
+  void DrawCursor(Canvas* canvas);
+
   // Logical UTF-16 string data to be drawn.
   string16 text_;
 
   // Logical selection range and visual cursor position.
   SelectionModel selection_model_;
 
   // The cached cursor bounds; get these bounds with GetUpdatedCursorBounds.
   Rect cursor_bounds_;
 
   // The cursor visibility and insert mode.
@@ skipping 20 matching lines @@
   // The cached bounds and offset are invalidated by changes to the cursor,
   // selection, font, and other operations that adjust the visible text bounds.
   bool cached_bounds_and_offset_valid_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderText);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_H_