Module: HexaPDF::Layout::TextLayouter::SimpleTextSegmentation

Defined in:

lib/hexapdf/layout/text_layouter.rb

Overview

Implementation of a simple text segmentation algorithm.

The algorithm breaks TextFragment objects into objects wrapped by Box, Glue or Penalty items, and inserts additional Penalty items when needed:

• Any valid Unicode newline separator inserts a Penalty object describing a mandatory break.

  See www.unicode.org/reports/tr18/#Line_Boundaries

• Spaces and tabulators are wrapped by Glue objects, allowing breaks.

• Non-breaking spaces are wrapped into Penalty objects that prohibit line breaking.

• Hyphens are attached to the preceeding text fragment (or are a standalone text fragment) and followed by a Penalty object to allow a break.

• If a soft-hyphens is encountered, a hyphen wrapped by a Penalty object is inserted to allow a break.

• If a zero-width-space is encountered, a Penalty object is inserted to allow a break.

Constant Summary

BREAK_CHARS =

Breaks are detected at: space, tab, zero-width-space, non-breaking space, hyphen, soft-hypen and any valid Unicode newline separator

{}

Class Method Summary

• .call(items) ⇒ Object

  Breaks the items (an array of InlineBox and TextFragment objects) into atomic pieces wrapped by Box, Glue or Penalty items, and returns those as an array.

Class Method Details

.call(items) ⇒ Object

Breaks the items (an array of InlineBox and TextFragment objects) into atomic pieces wrapped by Box, Glue or Penalty items, and returns those as an array.

# File 'lib/hexapdf/layout/text_layouter.rb', line 228

def self.call(items)
  result = []
  glues = {}
  penalties = {}
  items.each do |item|
    if item.kind_of?(InlineBox)
      result << Box.new(item)
    else
      i = 0
      while i < item.items.size
        # Collect characters and kerning values until break character is encountered
        box_items = []
        while (glyph = item.items[i]) &&
            (glyph.kind_of?(Numeric) || !BREAK_CHARS.key?(glyph.str))
          box_items << glyph
          i += 1
        end

        # A hyphen belongs to the text fragment
        box_items << glyph if glyph && !glyph.kind_of?(Numeric) && glyph.str == '-'

        unless box_items.empty?
          result << Box.new(item.dup_attributes(box_items.freeze))
        end

        if glyph
          case glyph.str
          when ' '
            result << (glues[item.attributes_hash] ||=
                       Glue.new(item.dup_attributes([glyph].freeze)))
          when "\n", "\v", "\f", "\u{85}", "\u{2029}"
            result << (penalties[item.attributes_hash] ||=
                       Penalty.new(Penalty::PARAGRAPH_BREAK, 0))
          when "\u{2028}"
            result << Penalty.new(Penalty::LINE_BREAK, 0)
          when "\r"
            if !item.items[i + 1] || item.items[i + 1].kind_of?(Numeric) ||
                item.items[i + 1].str != "\n"
              result << (penalties[item.attributes_hash] ||=
                         Penalty.new(Penalty::PARAGRAPH_BREAK, 0))
            end
          when '-'
            result << Penalty::Standard
          when "\t"
            spaces = [item.style.font.decode_utf8(" ").first] * 8
            result << Glue.new(item.dup_attributes(spaces.freeze))
          when "\u{00AD}"
            frag = item.dup_attributes([item.style.font.decode_utf8("-").first].freeze)
            result << Penalty.new(Penalty::Standard.penalty, frag.width, item: frag)
          when "\u{00A0}"
            frag = item.dup_attributes([item.style.font.decode_utf8(" ").first].freeze)
            result << Penalty.new(Penalty::ProhibitedBreak.penalty, frag.width, item: frag)
          when "\u{200B}"
            result << Penalty.new(0)
          end
        end
        i += 1
      end
    end
  end
  result
end