class ChunkyPNG::Chunk::Base

The base chunk class is the superclass for every chunk type. It contains methods to write the chunk to an output stream.

A subclass should implement the content method, which gets called when the chunk gets written to a PNG datastream

@abstract

Attributes

type[RW]

The four-character type indicator for the chunk. This field is used to find the correct class for a chunk when it is loaded from a PNG stream. @return [String]

Public Class Methods

new(type, attributes = {}) click to toggle source

Initializes the chunk instance. @param [String] type The four character chunk type indicator. @param [Hash] attributes A hash of attributes to set on this chunk.

# File lib/chunky_png/chunk.rb, line 59
def initialize(type, attributes = {})
  self.type = type
  attributes.each { |k, v| send("#{k}=", v) }
end

Public Instance Methods

write(io) click to toggle source

Writes the chunk to the IO stream.

It will call the content method to get the content for this chunk, and will calculate and append the checksum automatically. @param [IO] io The IO stream to write to.

# File lib/chunky_png/chunk.rb, line 78
def write(io)
  write_with_crc(io, content || '')
end
write_with_crc(io, content) click to toggle source

Writes the chunk to the IO stream, using the provided content. The checksum will be calculated and appended to the stream. @param [IO] io The IO stream to write to. @param [String] content The content for this chunk.

# File lib/chunky_png/chunk.rb, line 68
def write_with_crc(io, content)
  io << [content.length].pack('N') << type << content
  io << [Zlib.crc32(content, Zlib.crc32(type))].pack('N')
end