Class: Pdfrb::Document::Layers

Inherits:
Object
  • Object
show all
Defined in:
lib/pdfrb/document/layers.rb

Overview

Facade for Optional Content Groups (layers). OCGs let authors mark content as belonging to a named layer that can be toggled on/off by the viewer (ISO 32000-2 §8.11).

Each layer is a /Type /OCG dictionary with a /Name. The Catalog gets an /OCProperties entry:

/OCGs — array of all OCG indirect refs.
/D — default viewing config:
/BaseState /ON, /OFF [list of off-by-default OCGs], etc.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(document) ⇒ Layers

Returns a new instance of Layers.



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# File 'lib/pdfrb/document/layers.rb', line 17

def initialize(document)
  @document = document
  @groups = []
end

Instance Attribute Details

#document ⇒ Object (readonly)

Returns the value of attribute document.



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# File 'lib/pdfrb/document/layers.rb', line 15

def document
  @document
end

#groups ⇒ Object (readonly)

Returns the value of attribute groups.



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# File 'lib/pdfrb/document/layers.rb', line 15

def groups
  @groups
end

Instance Method Details

#add(name, default_on: true) ⇒ Object

Add a named layer. @return [Pdfrb::Model::Cos::Dictionary] the OCG.



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# File 'lib/pdfrb/document/layers.rb', line 23

def add(name, default_on: true)
  ensure_oc_properties
  ocg = document.add(
    { Type: :OCG, Name: name },
    type: Pdfrb::Model::Cos::Dictionary
  )
  ref = Pdfrb::Model::Reference.new(ocg.oid, ocg.gen)
  @groups << { ref: ref, ocg: ocg, default_on: default_on }
  ocg
end

#sync! ⇒ Object

Write /OCProperties to the Catalog. Called automatically by #add but can be called again to refresh after external modifications.



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# File 'lib/pdfrb/document/layers.rb', line 36

def sync!
  return if @groups.empty?

  ocgs_array = @groups.map { |g| g[:ref] }
  off_array = @groups.reject { |g| g[:default_on] }.map { |g| g[:ref] }

  default_config = { BaseState: :ON }
  default_config[:OFF] = off_array unless off_array.empty?

  catalog = document.catalog
  catalog.value[:OCProperties] = {
    OCGs: ocgs_array,
    D: default_config,
  }
end