class ChunkyPNG::Chunk::InternationalText

The InternationalText (iTXt) chunk contains keyword/value metadata about the PNG stream, translated to a given locale.

The metadata in this chunk can be encoded using UTF-8 characters. Moreover, it is possible to define the language of the metadata, and give a translation of the keyword name. Finally, it supports bot compressed and uncompressed values.

www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.iTXt

@see ChunkyPNG::Chunk::Text @see ChunkyPNG::Chunk::CompressedText

Attributes

compressed[RW]
compression[RW]
keyword[RW]
language_tag[RW]
text[RW]
translated_keyword[RW]

Public Class Methods

new(keyword, text, language_tag = '', translated_keyword = '', compressed = ChunkyPNG::UNCOMPRESSED_CONTENT, compression = ChunkyPNG::COMPRESSION_DEFAULT) click to toggle source
Calls superclass method ChunkyPNG::Chunk::Base.new
# File lib/chunky_png/chunk.rb, line 375
def initialize(keyword, text, language_tag = '', translated_keyword = '', compressed = ChunkyPNG::UNCOMPRESSED_CONTENT, compression = ChunkyPNG::COMPRESSION_DEFAULT)
  super('iTXt')
  @keyword = keyword
  @text = text
  @language_tag = language_tag
  @translated_keyword = translated_keyword
  @compressed = compressed
  @compression = compression
end
read(type, content) click to toggle source

Reads the tTXt chunk. @param type [String] The four character chunk type indicator (= “iTXt”). @param content [String] The content read from the chunk. @return [ChunkyPNG::Chunk::InternationalText] The new End chunk instance. @raise [ChunkyPNG::InvalidUTF8] If the chunk contains data that is not UTF8-encoded text. @raise [ChunkyPNG::NotSupported] If the chunk refers to an unsupported compression method.

Currently uncompressed data and deflate are supported.
# File lib/chunky_png/chunk.rb, line 392
def self.read(type, content)
  keyword, compressed, compression, language_tag, translated_keyword, text = content.unpack('Z*CCZ*Z*a*')
  raise ChunkyPNG::NotSupported, "Compression flag #{compressed.inspect} not supported!" unless compressed == ChunkyPNG::UNCOMPRESSED_CONTENT || compressed == ChunkyPNG::COMPRESSED_CONTENT
  raise ChunkyPNG::NotSupported, "Compression method #{compression.inspect} not supported!" unless compression == ChunkyPNG::COMPRESSION_DEFAULT

  text = Zlib::Inflate.inflate(text) if compressed == ChunkyPNG::COMPRESSED_CONTENT

  text.force_encoding('utf-8')
  raise ChunkyPNG::InvalidUTF8, "Invalid unicode encountered in iTXt chunk" unless text.valid_encoding?

  translated_keyword.force_encoding('utf-8')
  raise ChunkyPNG::InvalidUTF8, "Invalid unicode encountered in iTXt chunk" unless translated_keyword.valid_encoding?

  new(keyword, text, language_tag, translated_keyword, compressed, compression)
end

Public Instance Methods

content() click to toggle source

Assembles the content to write to the stream for this chunk. @return [String] The binary content that should be written to the datastream.

# File lib/chunky_png/chunk.rb, line 410
def content
  text_field = text.encode('utf-8')
  text_field = (compressed == ChunkyPNG::COMPRESSED_CONTENT) ? Zlib::Deflate.deflate(text_field) : text_field

  [keyword, compressed, compression, language_tag, translated_keyword.encode('utf-8'), text_field].pack('Z*CCZ*Z*a*')
end