Class: ChunkyPNG::Chunk::InternationalText

Inherits:
Base
  • Object
show all
Defined in:
lib/chunky_png/chunk.rb

Overview

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 Also:

Instance Attribute Summary collapse

Attributes inherited from Base

#type

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Base

#write, #write_with_crc

Constructor Details

#initialize(keyword, text, language_tag = '', translated_keyword = '', compressed = ChunkyPNG::UNCOMPRESSED_CONTENT, compression = ChunkyPNG::COMPRESSION_DEFAULT) ⇒ InternationalText

Returns a new instance of InternationalText.



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# 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

Instance Attribute Details

#compressed ⇒ Object

Returns the value of attribute compressed.



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# File 'lib/chunky_png/chunk.rb', line 373

def compressed
  @compressed
end

#compression ⇒ Object

Returns the value of attribute compression.



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# File 'lib/chunky_png/chunk.rb', line 373

def compression
  @compression
end

#keyword ⇒ Object

Returns the value of attribute keyword.



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# File 'lib/chunky_png/chunk.rb', line 373

def keyword
  @keyword
end

#language_tag ⇒ Object

Returns the value of attribute language_tag.



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# File 'lib/chunky_png/chunk.rb', line 373

def language_tag
  @language_tag
end

#text ⇒ Object

Returns the value of attribute text.



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# File 'lib/chunky_png/chunk.rb', line 373

def text
  @text
end

#translated_keyword ⇒ Object

Returns the value of attribute translated_keyword.



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# File 'lib/chunky_png/chunk.rb', line 373

def translated_keyword
  @translated_keyword
end

Class Method Details

.read(type, content) ⇒ ChunkyPNG::Chunk::InternationalText

Reads the tTXt chunk.

Parameters:

  • type (String) —

    The four character chunk type indicator (= “iTXt”).

  • content (String) —

    The content read from the chunk.

Returns:

Raises:

  • (ChunkyPNG::InvalidUTF8) —

    If the chunk contains data that is not UTF8-encoded text.

  • (ChunkyPNG::NotSupported) —

    If the chunk refers to an unsupported compression method. Currently uncompressed data and deflate are supported.



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# 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

Instance Method Details

#content ⇒ String

Assembles the content to write to the stream for this chunk.

Returns:

  • (String) —

    The binary content that should be written to the datastream.



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# 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