Class: ChunkyPNG::Chunk::CompressedText

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

Overview

The CompressedText (zTXt) chunk contains keyword/value metadata about the PNG stream. In this chunk, the value is compressed using Deflate compression.

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, value) ⇒ CompressedText

Returns a new instance of CompressedText.



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# File 'lib/chunky_png/chunk.rb', line 301

def initialize(keyword, value)
  super('zTXt')
  @keyword, @value = keyword, value
end

Instance Attribute Details

#keyword ⇒ Object

Returns the value of attribute keyword.



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# File 'lib/chunky_png/chunk.rb', line 299

def keyword
  @keyword
end

#value ⇒ Object

Returns the value of attribute value.



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# File 'lib/chunky_png/chunk.rb', line 299

def value
  @value
end

Class Method Details

.read(type, content) ⇒ Object

Raises:



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# File 'lib/chunky_png/chunk.rb', line 306

def self.read(type, content)
  keyword, compression, value = content.unpack('Z*Ca*')
  raise ChunkyPNG::NotSupported, "Compression method #{compression.inspect} not supported!" unless compression == ChunkyPNG::COMPRESSION_DEFAULT
  new(keyword, Zlib::Inflate.inflate(value))
end

Instance Method Details

#content ⇒ Object

Creates the content to write to the stream, by concatenating the keyword with the deflated value, joined by a null character.

Returns:

  • The content that should be written to the datastream.



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# File 'lib/chunky_png/chunk.rb', line 316

def content
  [keyword, ChunkyPNG::COMPRESSION_DEFAULT, Zlib::Deflate.deflate(value)].
    pack('Z*Ca*')
end