Class: Arrolio::Renderer::AccessibilityTagger

Inherits:
Object
  • Object
show all
Defined in:
lib/arrolio/renderer/accessibility_tagger.rb

Overview

Builds marked-content property lists for PDF/UA accessibility. Wraps non-text content (images, formulas) with /Alt and /ActualText entries so screen readers can access the semantic meaning even when the visual rendering is a rasterized image or a flattened formula.

In the PDF content stream, marked content looks like:

/MP << /Alt (alternative text) >> BDC
... drawing operators ...
EMC

This class builds the property list dictionaries; the renderer wraps them in BDC/EMC operators when drawing.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(document) ⇒ AccessibilityTagger

Returns a new instance of AccessibilityTagger.



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 21

def initialize(document)
  @document = document
  @sequence = 0
end

Instance Attribute Details

#document ⇒ Object (readonly)

Returns the value of attribute document.



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 19

def document
  @document
end

Instance Method Details

#actual_text_property(text) ⇒ Object

Builds a property list for actual text (the visible text representation of non-text content, e.g. a formula's flattened text).



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 41

def actual_text_property(text)
  return nil if text.nil? || text.to_s.empty?

  @document.add(
    { ActualText: text.to_s },
    type: Pdfrb::Model::Cos::Dictionary
  )
end

#alt_property(alt_text) ⇒ Object

Builds a property list dictionary for an image's alt text. Returns a Pdfrb reference to the dictionary, or nil if no alt text is provided.



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 29

def alt_property(alt_text)
  return nil if alt_text.nil? || alt_text.to_s.empty?

  @document.add(
    { Alt: alt_text.to_s },
    type: Pdfrb::Model::Cos::Dictionary
  )
end

#combined_property(alt_text: nil, actual_text: nil) ⇒ Object

Combines alt + actual text into a single property list. When both are present, the dictionary carries both entries.



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 52

def combined_property(alt_text: nil, actual_text: nil)
  props = {}
  props[:Alt] = alt_text.to_s if alt_text && !alt_text.to_s.empty?
  props[:ActualText] = actual_text.to_s if actual_text && !actual_text.to_s.empty?
  return nil if props.empty?

  @document.add(props, type: Pdfrb::Model::Cos::Dictionary)
end

#next_tag ⇒ Object

Next unique marked-content sequence number. Used by the renderer to tag BDC/EMC pairs so structure-tree entries can reference them.



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# File 'lib/arrolio/renderer/accessibility_tagger.rb', line 64

def next_tag
  @sequence += 1
  :"MC#{@sequence}"
end