Module: Idml::Render::Renderers::KeepPolicy

Defined in:
lib/idml/render/renderers/keep_policy.rb

Overview

Paragraph deferral policy (keep options + forced breaks): decides whether a paragraph moves wholly to the next frame/column instead of being split. Honors StartParagraph forced breaks, KeepAllLinesTogether, the KeepFirstLines / KeepLastLines partial windows (measured-line-count approximation), and KeepWithNext. Pure predicates over the paragraph chain state and frame geometry — no canvas, no emission (MECE: TextFrameRenderer owns flow and emission; FrameMetrics owns frame positioning).

Constant Summary collapse

BREAK_MODES = 
%w[
  NextPage NextColumn NextFrame NextOddPage NextEvenPage
].freeze

Class Method Summary collapse

Class Method Details

.first_window_break?(paragraph, lines_fit) ⇒ Boolean 



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# File 'lib/idml/render/renderers/keep_policy.rb', line 69

def first_window_break?(paragraph, lines_fit)
  paragraph.keep_first_lines &&
    lines_fit < paragraph.keep_first_lines
end

.keep_all_lines_break?(paragraph, layout_frame, font, cursor_y, bottom_limit) ⇒ Boolean

KeepAllLinesTogether: defer when the paragraph cannot fully fit the remaining space.



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# File 'lib/idml/render/renderers/keep_policy.rb', line 43

def keep_all_lines_break?(paragraph, layout_frame, font,
                          cursor_y, bottom_limit)
  return false unless paragraph.keep_all_lines_together

  height = paragraph_block_height(paragraph, layout_frame, font)
  (cursor_y - height) < bottom_limit
end

.keep_windows_break?(paragraph, layout_frame, font, cursor_y, bottom_limit) ⇒ Boolean

Partial keep windows, approximated by measured line counts: KeepFirstLines defers when fewer than N lines fit; KeepLastLines defers when the overflow tail for the next frame would strand fewer than N lines.



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# File 'lib/idml/render/renderers/keep_policy.rb', line 55

def keep_windows_break?(paragraph, layout_frame, font,
                        cursor_y, bottom_limit)
  return false unless paragraph.keep_first_lines ||
    paragraph.keep_last_lines

  height = paragraph_block_height(paragraph, layout_frame, font)
  return false if (cursor_y - height) >= bottom_limit

  leading = FrameMetrics.leading_for(paragraph)
  lines_fit = [((cursor_y - bottom_limit) / leading).floor, 0].max
  first_window_break?(paragraph, lines_fit) ||
    last_window_break?(paragraph, lines_fit, height, leading)
end

.keep_with_next_break?(paragraph, next_paragraph, layout_frame, font, cursor_y, bottom_limit) ⇒ Boolean

KeepWithNext: this paragraph defers when the next paragraph is forced to the next frame, or when the next paragraph's first line would not fit after this one.



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# File 'lib/idml/render/renderers/keep_policy.rb', line 85

def keep_with_next_break?(paragraph, next_paragraph,
                          layout_frame, font, cursor_y,
                          bottom_limit)
  return false unless keepable_pair?(paragraph, next_paragraph)
  return true if paragraph_break?(next_paragraph)

  height = paragraph_block_height(paragraph, layout_frame, font)
  (cursor_y - height - FrameMetrics.leading_for(next_paragraph)) <
    bottom_limit
end

.keepable_pair?(paragraph, next_paragraph) ⇒ Boolean 



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# File 'lib/idml/render/renderers/keep_policy.rb', line 96

def keepable_pair?(paragraph, next_paragraph)
  !paragraph.keep_with_next.nil? && !next_paragraph.nil?
end

.last_window_break?(paragraph, lines_fit, height, leading) ⇒ Boolean 



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# File 'lib/idml/render/renderers/keep_policy.rb', line 74

def last_window_break?(paragraph, lines_fit, height, leading)
  return false unless paragraph.keep_last_lines

  total_lines = [(height / leading).ceil, 1].max
  lines_fit.positive? &&
    (total_lines - lines_fit) < paragraph.keep_last_lines
end

.paragraph_block_height(paragraph, layout_frame, font) ⇒ Object 



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# File 'lib/idml/render/renderers/keep_policy.rb', line 107

def paragraph_block_height(paragraph, layout_frame, font)
  wrap_width = TextEngine::VerticalLayout.wrap_width(
    layout_frame, paragraph.right_indent || 0
  )
  TextEngine::Measurement.paragraph_height(
    paragraph, font, wrap_width
  )
end

.paragraph_break?(paragraph) ⇒ Boolean

True when the paragraph requests a forced break to the next frame/column (StartParagraph). All break flavors act at frame/column granularity.



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# File 'lib/idml/render/renderers/keep_policy.rb', line 103

def paragraph_break?(paragraph)
  BREAK_MODES.include?(paragraph.start_paragraph)
end

.paragraph_deferred?(paragraph, next_paragraph, layout_frame, font, cursor_y, bottom_limit, placed_any) ⇒ Boolean

True when the paragraph should move wholly to the next frame: a StartParagraph forced break, or a keep rule that the remaining space violates (never for the frame's first paragraph, so progress is always made).



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# File 'lib/idml/render/renderers/keep_policy.rb', line 26

def paragraph_deferred?(paragraph, next_paragraph,
                        layout_frame, font, cursor_y,
                        bottom_limit, placed_any)
  return true if paragraph_break?(paragraph) && placed_any
  return false unless placed_any
  return true if keep_with_next_break?(paragraph, next_paragraph,
                                       layout_frame, font,
                                       cursor_y, bottom_limit)

  keep_all_lines_break?(paragraph, layout_frame, font,
                        cursor_y, bottom_limit) ||
    keep_windows_break?(paragraph, layout_frame, font,
                        cursor_y, bottom_limit)
end