libtxt: refactoring of paragraph layout to improve text justification (#4178)

This changes Paragraph::Layout to iterate line-by-line through the text.
For each line, Layout scans for word boundaries and adds extra space between
words if the line is justified.

third_party/txt/src/txt/paragraph.h

@@ -71,6 +71,7 @@ class Paragraph {
   //
   // Layout calculates the positioning of all the glyphs. Must call this method
   // before Painting and getting any statistics from this class.
+  void OldLayout(double width, bool force = false);
   void Layout(double width, bool force = false);
 
   // Paints the Laid out text onto the supplied SkCanvas at (x, y) offset from
@@ -138,7 +139,7 @@ class Paragraph {
   // Returns the number of lines the paragraph takes up. If the text exceeds the
   // amount width and maxlines provides, Layout() truncates the extra text from
   // the layout and this will return the max lines allowed.
-  int GetLineCount() const;
+  size_t GetLineCount() const;
 
   // Checks if the layout extends past the maximum lines and had to be
   // truncated.
@@ -212,13 +213,9 @@ class Paragraph {
   // Holds the laid out x positions of each glyph.
   std::vector<GlyphLine> glyph_position_x_;
 
-  // Set of glyph IDs that correspond to whitespace.
-  std::set<GlyphID> whitespace_set_;
-
   // The max width of the paragraph as provided in the most recent Layout()
   // call.
   double width_ = -1.0f;
-  size_t lines_ = 0;
   double max_intrinsic_width_ = 0;
   double min_intrinsic_width_ = 0;
   double alphabetic_baseline_ = FLT_MAX;
@@ -253,22 +250,10 @@ class Paragraph {
       std::unordered_map<std::string, std::shared_ptr<minikin::FontCollection>>&
           collection_map);
 
-  // Calculates the GlyphIDs of all whitespace characters present in the text
-  // between start and end. THis is used to correctly add extra whitespace when
-  // justifying.
-  void FillWhitespaceSet(size_t start, size_t end, hb_font_t* hb_font);
-
   // Calculate the starting X offset of a line based on the line's width and
   // alignment.
   double GetLineXOffset(size_t line);
 
-  // Calculates and amends the layout for one line to be justified.
-  void JustifyLine(std::vector<const SkTextBlobBuilder::RunBuffer*>& buffers,
-                   std::vector<size_t>& buffer_sizes,
-                   int word_count,
-                   double& justify_spacing,
-                   double multiplier = 1);
-
   // Creates and draws the decorations onto the canvas.
   void PaintDecorations(SkCanvas* canvas,
                         double x,

third_party/txt/tests/paragraph_unittests.cc

@@ -1260,7 +1260,7 @@ TEST_F(ParagraphTest, LongWordParagraph) {
   ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
   ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
   ASSERT_EQ(paragraph->records_[0].style().color, text_style.color);
-  ASSERT_EQ(paragraph->GetLineCount(), 4);
+  ASSERT_EQ(paragraph->GetLineCount(), 4ull);
   ASSERT_TRUE(Snapshot());
 }
 
@@ -1446,7 +1446,7 @@ TEST_F(ParagraphTest, HyphenBreakParagraph) {
   ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
   ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
   ASSERT_EQ(paragraph->records_[0].style().color, text_style.color);
-  ASSERT_EQ(paragraph->GetLineCount(), 5);
+  ASSERT_EQ(paragraph->GetLineCount(), 5ull);
   ASSERT_TRUE(Snapshot());
 }
 
@@ -1490,7 +1490,7 @@ TEST_F(ParagraphTest, RepeatLayoutParagraph) {
   ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
   ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
   ASSERT_EQ(paragraph->records_[0].style().color, text_style.color);
-  ASSERT_EQ(paragraph->GetLineCount(), 12);
+  ASSERT_EQ(paragraph->GetLineCount(), 12ull);
 
   // Second Layout.
   SetUp();
@@ -1506,7 +1506,7 @@ TEST_F(ParagraphTest, RepeatLayoutParagraph) {
   ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
   ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
   ASSERT_EQ(paragraph->records_[0].style().color, text_style.color);
-  ASSERT_EQ(paragraph->GetLineCount(), 6);
+  ASSERT_EQ(paragraph->GetLineCount(), 6ull);
   ASSERT_TRUE(Snapshot());
 }