Reduce the number of text reshaping in RenderText

ui/gfx/render_text.h

Index: ui/gfx/render_text.h
diff --git a/ui/gfx/render_text.h b/ui/gfx/render_text.h
index 6c094dcc36d51c6e29574aeedcedb47376a3a38c..5fb3865b6f60c7e6cda8655eea7716ca9dd7dcc7 100644
--- a/ui/gfx/render_text.h
+++ b/ui/gfx/render_text.h
@@ -274,8 +274,6 @@ class GFX_EXPORT RenderText {
   void SetElideBehavior(ElideBehavior elide_behavior);
   ElideBehavior elide_behavior() const { return elide_behavior_; }
 
-  const base::string16& layout_text() const { return layout_text_; }
-
   const Rect& display_rect() const { return display_rect_; }
   void SetDisplayRect(const Rect& r);
 
@@ -358,6 +356,11 @@ class GFX_EXPORT RenderText {
   // |GetTextDirection()|, not the direction of a particular run.
   VisualCursorDirection GetVisualDirectionOfLogicalEnd();
 
+  // Returns the text used for layout, which may be obscured,
+  // truncated or elided. The subclass may compute elided text on the fly,
+  // or use precomputed the elided text.
+  virtual const base::string16& GetLayoutText() = 0;
+
   // Returns the size required to display the current string (which is the
   // wrapped size in multiline mode). The returned size does not include space
   // reserved for the cursor or the offset text shadows.
@@ -448,6 +451,10 @@ class GFX_EXPORT RenderText {
  protected:
   RenderText();
 
+  const base::string16& layout_text() const { return layout_text_; }
+  const base::string16& elided_text() const { return elided_text_; }
+  bool text_elided() const { return text_elided_; }
+
   const BreakList<SkColor>& colors() const { return colors_; }
   const std::vector<BreakList<bool> >& styles() const { return styles_; }
 
@@ -515,14 +522,20 @@ class GFX_EXPORT RenderText {
   // or bounds changes may invalidate returned values.
   virtual std::vector<Rect> GetSubstringBounds(const Range& range) = 0;
 
-  // Convert between indices into |text_| and indices into |obscured_text_|,
-  // which differ when the text is obscured. Regardless of whether or not the
-  // text is obscured, the character (code point) offsets always match.
-  virtual size_t TextIndexToLayoutIndex(size_t index) const = 0;
-  virtual size_t LayoutIndexToTextIndex(size_t index) const = 0;
+  // Convert between indices into |text_| and indices into
+  // GetLayoutText(), which differ when the text is obscured,
+  // truncated or elided. Regardless of whether or not the text is
+  // obscured, the character (code point) offsets always match.
+  virtual size_t TextIndexToLayoutIndex(size_t index) = 0;
+  virtual size_t LayoutIndexToTextIndex(size_t index) = 0;
+
+  // Notifies that layout text, or attributes that affects layout text
+  // shape have changed. |text_changed| is true if the content of the
+  // |layouttext_| has changed, not just attributes.

[msw, 2015/02/12 22:45:06]

nit: |layout_text_|

[oshima, 2015/02/13 00:29:43]

Done.

+  virtual void OnLayoutTextShapeChanged(bool text_changed) = 0;
 
-  // Reset the layout to be invalid.
-  virtual void ResetLayout() = 0;
+  // Notifies that attributes that affects elided text shape has changed.

[msw, 2015/02/12 22:45:06]

nit: s/affects/affect/ and s/has/have/

[oshima, 2015/02/13 00:29:43]

Done.

+  virtual void OnElidedTextShapeChanged() = 0;
 
   // Ensure the text is laid out, lines are computed, and |lines_| is valid.
   virtual void EnsureLayout() = 0;
@@ -530,8 +543,8 @@ class GFX_EXPORT RenderText {
   // Draw the text.
   virtual void DrawVisualText(Canvas* canvas) = 0;
 
-  // Returns the text used for layout, which may be obscured or truncated.
-  const base::string16& GetLayoutText() const;
+  // Update the elided text.
+  void UpdateElidedText(float visual_width);
 
   // Returns layout text positions that are suitable for breaking lines.
   const BreakList<size_t>& GetLineBreaks();
@@ -609,10 +622,14 @@ class GFX_EXPORT RenderText {
   void MoveCursorTo(size_t position, bool select);
 
   // Updates |layout_text_| if the text is obscured or truncated.
+  // This will triggers |elided_text_| update.

[msw, 2015/02/12 22:45:06]

nit: merge the comments to something simpler, like "Updates |layout_text_| and
|elided_text_| as needed."

[oshima, 2015/02/13 00:29:43]

Done.

   void UpdateLayoutText();

[msw, 2015/02/12 22:45:06]

I like the pattern of On*Changed, and I could see this being renamed
OnText[Content|Attribute]Changed or maybe OnLayoutAttributeChanged or similar.
WDYT?

[oshima, 2015/02/13 00:29:43]

Changed to OnTextAttributeChanged

 
   // Elides |text| as needed to fit in the |available_width| using |behavior|.
+  // |text_width| is the pre-calculated width of the text shaped by this render
+  // text, or pass 0 if the width is unknown.
   base::string16 Elide(const base::string16& text,
+                       float text_width,
                        float available_width,
                        ElideBehavior behavior);
 
@@ -694,9 +711,14 @@ class GFX_EXPORT RenderText {
   // The behavior for eliding, fading, or truncating.
   ElideBehavior elide_behavior_;
 
-  // The obscured and/or truncated text that will be displayed.
+  // The obscured and/or truncated text, before elided.

[msw, 2015/02/12 22:45:06]

Rename this, it doesn't match the semantics of GetLayoutText, which elides the
text as needed... Perhaps rename them as an intermediate |unelided_layout_text_|
and a definitive |layout_text_|, or some other pattern.

[oshima, 2015/02/13 00:29:43]

kept layout_text_ and changed elided_text_ to display_text_ as discussed
offline. let me know if you misunderstood something.

   base::string16 layout_text_;
 
+  // The elided text. This is empty if the text does not have to be elided.
+  base::string16 elided_text_;

[msw, 2015/02/12 22:45:06]

nit: reorder |elide_behavior_| to come immediately before |elided_text_| and
|text_elided_|.

[oshima, 2015/02/13 00:29:43]

Done.

+
+  bool text_elided_;

[msw, 2015/02/12 22:45:06]

nit: add a comment like "True if the text is elided given the current behavior
and display area."

[oshima, 2015/02/13 00:29:43]

Done.

+
   // Whether newline characters should be replaced with newline symbols.
   bool replace_newline_chars_with_symbols_;