Windows implementation of multiline 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 34277400b7369e28c41e120950e357555c8c9415..8dd3144142ff1b98f244e779b4e1faa1ba554e32 100644
--- a/ui/gfx/render_text.h
+++ b/ui/gfx/render_text.h
@@ -111,6 +111,38 @@ class StyleIterator {
   DISALLOW_COPY_AND_ASSIGN(StyleIterator);
 };
 
+// Line segments are slices of the layout text to be rendered on a single line.
+// This structure holds the logical and visual position information for a line
+// segment.
+struct LineSegment {
+  // X coordinates of this line segment in text coordinate space.
+  ui::Range x_range;
+
+  // The character range this segment corresponds to.
+  ui::Range char_range;
+
+  // Index of the text run that generated this segment.
+  size_t run;
+};
+
+// Holds a list of line segments and metrics for a line.
+struct Line {
+  Line();
+
+  // Segments that make up this line in visual order.
+  std::vector<LineSegment> segments;
+
+  // Total size of this line. Width is the sum of |segment| widths, height is
+  // the maximum height among |segments|.
+  gfx::Size size;

[Alexei Svitkine (slow), 2013/08/27 15:40:38]

Nit: Remove gfx.

[ckocagil, 2013/08/28 19:16:26]

Done.

+
+  // Sum of the |height| fields of preceding lines.
+  int preceding_heights;
+
+  // Maximum baseline of all runs on this line.
+  int baseline;
+};
+
 }  // namespace internal
 
 // RenderText represents an abstract model of styled text and its corresponding
@@ -186,6 +218,11 @@ class UI_EXPORT RenderText {
   // cleared when SetText or SetObscured is called.
   void SetObscuredRevealIndex(int index);
 
+  // TODO(ckocagil): Multiline text rendering is currently only supported on
+  // Windows. Support other platforms.
+  bool multiline() const { return multiline_; }
+  void SetMultiline(bool multiline);
+
   // Set the maximum length of the displayed layout text, not the actual text.
   // A |length| of 0 forgoes a hard limit, but does not guarantee proper
   // functionality of very long strings. Applies to subsequent SetText calls.
@@ -287,6 +324,11 @@ class UI_EXPORT RenderText {
   // the margin area of text shadows.
   virtual Size GetStringSize() = 0;
 
+  // Returns the size required to display the current multiline text, which is
+  // horizontally capped by the width of |display_rect()|.
+  // TODO(ckocagil): Merge with GetContentWidth.
+  virtual Size GetMultilineTextSize() = 0;
+
   // Returns the width of content, which reserves room for the cursor if
   // |cursor_enabled_| is true.
   int GetContentWidth();
@@ -348,6 +390,9 @@ class UI_EXPORT RenderText {
   const BreakList<SkColor>& colors() const { return colors_; }
   const std::vector<BreakList<bool> >& styles() const { return styles_; }
 
+  const std::vector<internal::Line>& lines() const { return lines_; }
+  void set_lines(std::vector<internal::Line>* lines) { lines_.swap(*lines); }
+
   const Vector2d& GetUpdatedDisplayOffset();
 
   void set_cached_bounds_and_offset_valid(bool valid) {
@@ -403,10 +448,10 @@ class UI_EXPORT RenderText {
   // which means it is a grapheme boundary or the first character in the text.
   virtual bool IsCursorablePosition(size_t position) = 0;
 
-  // Reset the layout to be invalid.
+  // Reset the layout and |lines_| to be invalid.

[msw, 2013/08/27 01:30:52]

I'd avoid describing the internals of a pure virtual function, especially since
Linux/Mac doesn't do this. (I'd just remove this comment change for now).
Eventually a onsolidated RenderText impl should simply mark the layout (and
lines_) as invalid, and then that can be explained here.

[ckocagil, 2013/08/28 18:01:45]

Done.

   virtual void ResetLayout() = 0;
 
-  // Ensure the text is laid out.
+  // Ensure the text is laid out, lines are computed, and |lines_| is valid.
   virtual void EnsureLayout() = 0;
 
   // Draw the text.
@@ -415,22 +460,29 @@ class UI_EXPORT RenderText {
   // Returns the text used for layout, which may be obscured or truncated.
   const base::string16& GetLayoutText() const;
 
+  // Returns layout text positions that are suitable for breaking lines at.
+  const BreakList<size_t>& GetLineBreaks();
+
   // Apply (and undo) temporary composition underlines and selection colors.
   void ApplyCompositionAndSelectionStyles();
   void UndoCompositionAndSelectionStyles();
 
-  // Returns the text offset from the origin after applying text alignment and
+  // Returns the line offset from the origin after applying text alignment and
   // display offset.
-  Vector2d GetTextOffset();
+  Vector2d GetLineOffset(size_t line_number);
 
-  // Convert points from the text space to the view space and back.
-  // Handles the display area, display offset, and the application LTR/RTL mode.
+  // Convert points from the text space to the view space and back. Handles the
+  // display area, display offset, application LTR/RTL mode and multi-line.
   Point ToTextPoint(const Point& point);
   Point ToViewPoint(const Point& point);
 
-  // Returns the text offset from the origin, taking into account text alignment
+  // Convert the range in text coordinates to rects in view coordinates that
+  // cover the given range.
+  std::vector<Rect> TextBoundsToViewBounds(const ui::Range& x);
+
+  // Returns the line offset from the origin, taking into account text alignment
   // only.
-  Vector2d GetAlignmentOffset();
+  Vector2d GetAlignmentOffset(size_t line_number);
 
   // Applies fade effects to |renderer|.
   void ApplyFadeEffects(internal::SkiaTextRenderer* renderer);
@@ -457,6 +509,8 @@ class UI_EXPORT RenderText {
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, EdgeSelectionModels);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, GetTextOffset);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, GetTextOffsetHorizontalDefaultInRTL);
+  FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_MinWidth);
+  FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_NormalWidth);
 
   // Set the cursor to |position|, with the caret trailing the previous
   // grapheme, or if there is no previous grapheme, leading the cursor position.
@@ -547,6 +601,10 @@ class UI_EXPORT RenderText {
   // The obscured and/or truncated text that will be displayed.
   base::string16 layout_text_;
 
+  // Whether the text should be broken into multiple lines. Uses the width of
+  // |display_rect_| as the width cap.
+  bool multiline_;
+
   // Fade text head and/or tail, if text doesn't fit into |display_rect_|.
   bool fade_head_;
   bool fade_tail_;
@@ -574,6 +632,14 @@ class UI_EXPORT RenderText {
   // Text shadows to be drawn.
   ShadowValues text_shadows_;
 
+  // BreakList to find valid positions to break the line at.
+  BreakList<size_t> line_breaks_;
+
+  // Lines computed by EnsureLayout. |ResetLayout()| implicitly invalidates

[msw, 2013/08/27 01:30:52]

nit: I liked the old comment format better; ResetLayout() is pure virtual, so we
can't really describe its behavior here. But describing when lines *should* be
reset in terms of layout and display rect updates seems okay. Consider: "Lines
computed by EnsureLayout; these should be invalidated with ResetLayout and on
|display_rect_| changes."

[ckocagil, 2013/08/28 18:01:45]

Done.

+  // |lines_|. Should be explicitly emptied to invalidate in other conditions,
+  // such as |display_rect_| changes.
+  std::vector<internal::Line> lines_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderText);
 };