Separate selection highlight from pango layout

ui/gfx/render_text.h

Index: ui/gfx/render_text.h
===================================================================
--- ui/gfx/render_text.h	(revision 109708)
+++ ui/gfx/render_text.h	(working copy)
@@ -209,17 +209,16 @@
   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;
@@ -228,6 +227,12 @@
   // 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;
@@ -249,9 +254,6 @@
   // 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.
@@ -263,6 +265,10 @@
   // 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_;