class ChunkyPNG::Datastream
The Datastream class represents a PNG formatted datastream. It supports both reading from and writing to strings, streams and files.
A PNG datastream begins with the PNG signature, and than contains multiple chunks, starting with a header (IHDR) chunk and finishing with an end (IEND) chunk.
@see ChunkyPNG::Chunk
Constants
- SIGNATURE
The signature that each PNG file or stream should begin with.
Attributes
The chunks that together compose the images pixel data. @return [Array<ChunkyPNG::Chunk::ImageData>]
The empty chunk that signals the end of this datastream @return [ChunkyPNG::Chunk::Header]
The header chunk of this datastream. @return [ChunkyPNG::Chunk::Header]
All other chunks in this PNG file. @return [Array<ChunkyPNG::Chunk::Generic>]
The chunk containing the image's palette. @return [ChunkyPNG::Chunk::Palette]
The chunk containing the transparency information of the palette. @return [ChunkyPNG::Chunk::Transparency]
Public Class Methods
Returns an empty stream using binary encoding that can be used as stream to encode to. @return [String] An empty, binary string.
# File lib/chunky_png/datastream.rb, line 157 def self.empty_bytearray ChunkyPNG::EMPTY_BYTEARRAY.dup end
Initializes a new Datastream instance.
# File lib/chunky_png/datastream.rb, line 41 def initialize @other_chunks = [] @data_chunks = [] end
Public Instance Methods
Returns an enumerator instance for this datastream's chunks. @return [Enumerable::Enumerator] An enumerator for the :each_chunk method. @see #each_chunk
# File lib/chunky_png/datastream.rb, line 131 def chunks enum_for(:each_chunk) end
Enumerates the chunks in this datastream.
This will iterate over the chunks using the order in which the chunks should appear in the PNG file.
@yield [chunk] Yields the chunks in this datastream, one by one in the correct order. @yieldparam [ChunkyPNG::Chunk::Base] chunk A chunk in this datastream. @see #chunks
# File lib/chunky_png/datastream.rb, line 119 def each_chunk yield(header_chunk) other_chunks.each { |chunk| yield(chunk) } yield(palette_chunk) if palette_chunk yield(transparency_chunk) if transparency_chunk data_chunks.each { |chunk| yield(chunk) } yield(end_chunk) end
Reads a PNG datastream from a string. @param [String] str The PNG encoded string to load from. @return [ChunkyPNG::Datastream] The loaded datastream instance.
# File lib/chunky_png/datastream.rb, line 55 def from_blob(str) from_io(StringIO.new(str)) end
Reads a PNG datastream from a file. @param [String] filename The path of the file to load from. @return [ChunkyPNG::Datastream] The loaded datastream instance.
# File lib/chunky_png/datastream.rb, line 64 def from_file(filename) ds = nil File.open(filename, 'rb') { |f| ds = from_io(f) } ds end
Reads a PNG datastream from an input stream @param [IO] io The stream to read from. @return [ChunkyPNG::Datastream] The loaded datastream instance.
# File lib/chunky_png/datastream.rb, line 73 def from_io(io) verify_signature!(io) ds = self.new until io.eof? chunk = ChunkyPNG::Chunk.read(io) case chunk when ChunkyPNG::Chunk::Header; ds.header_chunk = chunk when ChunkyPNG::Chunk::Palette; ds.palette_chunk = chunk when ChunkyPNG::Chunk::Transparency; ds.transparency_chunk = chunk when ChunkyPNG::Chunk::ImageData; ds.data_chunks << chunk when ChunkyPNG::Chunk::End; ds.end_chunk = chunk else ds.other_chunks << chunk end end return ds end
Returns the uncompressed image data, combined from all the IDAT chunks @return [String] The uncompressed image data for this datastream
# File lib/chunky_png/datastream.rb, line 147 def imagedata ChunkyPNG::Chunk::ImageData.combine_chunks(data_chunks) end
Returns all the textual metadata key/value pairs as hash. @return [Hash] A hash containing metadata fields and their values.
# File lib/chunky_png/datastream.rb, line 137 def metadata metadata = {} other_chunks.select do |chunk| metadata[chunk.keyword] = chunk.value if chunk.respond_to?(:keyword) end metadata end
Saves this datastream as a PNG file. @param [String] filename The filename to use.
# File lib/chunky_png/datastream.rb, line 170 def save(filename) File.open(filename, 'wb') { |f| write(f) } end
Encodes this datastream into a string. @return [String] The encoded PNG datastream.
# File lib/chunky_png/datastream.rb, line 176 def to_blob str = StringIO.new write(str) return str.string end
Verifies that the current stream is a PNG datastream by checking its signature.
This method reads the PNG signature from the stream, setting the current position of the stream directly after the signature, where the IHDR chunk should begin.
@param [IO] io The stream to read the PNG signature from. @raise [RuntimeError] An exception is raised if the PNG signature is not found at
the beginning of the stream.
# File lib/chunky_png/datastream.rb, line 99 def verify_signature!(io) signature = io.read(ChunkyPNG::Datastream::SIGNATURE.length) unless signature == ChunkyPNG::Datastream::SIGNATURE raise ChunkyPNG::SignatureMismatch, "PNG signature not found!" end end
Writes the datastream to the given output stream. @param [IO] io The output stream to write to.
# File lib/chunky_png/datastream.rb, line 163 def write(io) io << SIGNATURE each_chunk { |c| c.write(io) } end