Module: Idml::TextEngine::VerticalTextLayout

Defined in:
lib/idml/text_engine/vertical_text_layout.rb

Overview

Vertical (top-to-bottom, right-to-left) glyph layout for CJK vertical writing (StoryOrientation="Vertical"). Glyphs stay UPRIGHT — CJK ideographs render correctly stacked; Latin glyphs are not rotated to the vertical axis (documented approximation). Line breaking (and therefore kinsoku shori) is reused from LineBreaker against the column height.

Defined Under Namespace

Classes: PositionedGlyph

Class Method Summary collapse

Class Method Details

.column_height(frame) ⇒ Object

The frame's usable vertical extent for one column of text.



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# File 'lib/idml/text_engine/vertical_text_layout.rb', line 32

def self.column_height(frame)
  frame.height - (frame.inset_top || 0) - (frame.inset_bottom || 0)
end

.layout(glyphs:, frame:, leading:, size:, start_column: 0) ⇒ Object

Stacks glyphs into columns of at most the frame's text height; column 0 is the rightmost. start_column places the first column after already-used columns (multi-run frames). Returns [positioned_glyphs, next_column_index].



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# File 'lib/idml/text_engine/vertical_text_layout.rb', line 19

def self.layout(glyphs:, frame:, leading:, size:, start_column: 0)
  lines = TextEngine::LineBreaker.break(
    glyphs: glyphs, frame_width: column_height(frame),
  )
  positioned = []
  lines.each_with_index do |line, index|
    stack_column(positioned, line.glyphs, frame, leading, size,
                 index + start_column)
  end
  [positioned, start_column + lines.length]
end

.tatechuyoko_group(glyphs:, frame:, leading:, size:, start_column:) ⇒ Object

Positions a tate-chu-yoko group (e.g. the digits "12" kept horizontal inside vertical text): glyphs share one baseline at the top of the given column slot and advance left-to- right, centered in the slot. Returns [positioned_glyphs, next_column_index]; nil when the group is wider than the column height (caller falls back to stacked layout).



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# File 'lib/idml/text_engine/vertical_text_layout.rb', line 58

def self.tatechuyoko_group(glyphs:, frame:, leading:, size:,
                           start_column:)
  total = glyphs.sum(&:width)
  return nil if total > column_height(frame)

  right = frame.x + frame.width - (frame.inset_right || 0)
  slot_center = right - ((start_column + 0.5) * leading)
  x = slot_center - (total / 2.0)
  baseline_y = frame.y + frame.height - (frame.inset_top || 0) - size
  positioned = glyphs.map do |glyph|
    glyph_position = PositionedGlyph.new(
      codepoint: glyph.codepoint, x: x, y: baseline_y,
    )
    x += glyph.width
    glyph_position
  end
  [positioned, start_column + 1]
end