Class: Jif::Gif

Inherits:
Object
  • Object
show all
Defined in:
lib/jif.rb

Constant Summary collapse

END_OF_HEADER_AND_LFD =

Header and LFD are a fixed size

103
GIF_TRAILER =

0x3B

"00111011"
IMAGE_SEPARATOR =

0x2C

"00101100"
EXTENSION_INTRODUCER =

0x21

"00100001"
GRAPHICS_CONTROL_EXTENSION_LABEL =

Extension Labels

"11111001"
PLAIN_TEXT_LABEL =

0x01

"00000001"
APPLICATION_EXTENSION_LABEL =

0xFF

"11111111"
COMMENT_EXTENSION_LABEL =

0xFE

"11111110"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(file_name) ⇒ Gif

Returns a new instance of Gif.



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# File 'lib/jif.rb', line 22

def initialize(file_name)
  s = File.binread(file_name)
  bits = s.unpack("B*")[0]
  raise "Error: Unable to parse file. Gif must be GIF89a, found: #{b_to_h(bits[0..47])}" unless b_to_h(bits[0..47]) == "0x474946383961"

  @header = bits[0..47]
  @logical_screen_descriptor = bits[48..103]
  @canvas_width = logical_screen_descriptor[0..15]
  @canvas_height = logical_screen_descriptor[16..31]
  @packed_field = logical_screen_descriptor[32..39]
  @background_color_index = logical_screen_descriptor[40..47]
  @pixel_aspect_ratio = logical_screen_descriptor[48..74]
  @global_color_table_flag = packed_field[0]
  @color_resolution = packed_field[1..3]
  @sort_flag = packed_field[4]
  @size_of_global_color_table = packed_field[5..7]

  bits = bits[(END_OF_HEADER_AND_LFD + 1)..-1]
  if @global_color_table_flag == "1"
    @global_color_table = color_table_parser(bits, @size_of_global_color_table)
    bits = bits[@global_color_table.size..-1]
  end

  @tail = [] # An Array of hashes containing the remainder of the file broken into blocks
  until (bits[0..7] == GIF_TRAILER)
    if bits[0..7] == EXTENSION_INTRODUCER
      case bits[8..15]
      when GRAPHICS_CONTROL_EXTENSION_LABEL
        graphics_control_extension = graphics_control_extension_parser bits
        @tail.push graphics_control_extension
        bits = bits[graphics_control_extension[:total_block_size]..-1]
      when PLAIN_TEXT_LABEL, APPLICATION_EXTENSION_LABEL
        extension = extension_parser bits
        @tail.push extension
        bits = bits[extension[:total_block_size]..-1]
      when COMMENT_EXTENSION_LABEL
        comment_extension = comment_extension_parser bits
        @tail.push comment_extension
        bits = bits[comment_extension[:total_block_size]..-1]
      end
    elsif bits[0..7] == IMAGE_SEPARATOR
      image_descriptor = image_descriptor_parser bits
      bits = bits[image_descriptor[:total_block_size]..-1]
      local_color_table = nil
      if image_descriptor[:packed_field][:local_color_table_flag] == "1"
        local_color_table = color_table_parser(bits, image_descriptor[:packed_field][:size_of_local_color_table])
        bits = bits[local_color_table.size..-1]
      end
      image_data = image_data_parser bits
      data = {
        image_descriptor: image_descriptor,
        local_color_table: local_color_table,
        image_data: image_data,
      }
      @tail.push data

      bits = bits[data[:image_data][:total_block_size]..-1]
    else
      raise "Error: Unknown block header: #{bits[0..7]}"
    end
  end
end

Instance Attribute Details

#background_color_index ⇒ Object

Returns the value of attribute background_color_index.



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# File 'lib/jif.rb', line 17

def background_color_index
  @background_color_index
end

#canvas_height ⇒ Object

Returns the value of attribute canvas_height.



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# File 'lib/jif.rb', line 17

def canvas_height
  @canvas_height
end

#canvas_width ⇒ Object

Returns the value of attribute canvas_width.



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# File 'lib/jif.rb', line 17

def canvas_width
  @canvas_width
end

#color_resolution ⇒ Object

Returns the value of attribute color_resolution.



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# File 'lib/jif.rb', line 17

def color_resolution
  @color_resolution
end

#global_color_table ⇒ Object

Returns the value of attribute global_color_table.



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# File 'lib/jif.rb', line 17

def global_color_table
  @global_color_table
end

#global_color_table_flag ⇒ Object

Returns the value of attribute global_color_table_flag.



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# File 'lib/jif.rb', line 17

def global_color_table_flag
  @global_color_table_flag
end

#header ⇒ Object

Returns the value of attribute header.



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# File 'lib/jif.rb', line 17

def header
  @header
end

#logical_screen_descriptor ⇒ Object

Returns the value of attribute logical_screen_descriptor.



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# File 'lib/jif.rb', line 17

def logical_screen_descriptor
  @logical_screen_descriptor
end

#packed_field ⇒ Object

Returns the value of attribute packed_field.



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# File 'lib/jif.rb', line 17

def packed_field
  @packed_field
end

#pixel_aspect_ratio ⇒ Object

Returns the value of attribute pixel_aspect_ratio.



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# File 'lib/jif.rb', line 17

def pixel_aspect_ratio
  @pixel_aspect_ratio
end

#size_of_global_color_table ⇒ Object

Returns the value of attribute size_of_global_color_table.



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# File 'lib/jif.rb', line 17

def size_of_global_color_table
  @size_of_global_color_table
end

#sort_flag ⇒ Object

Returns the value of attribute sort_flag.



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# File 'lib/jif.rb', line 17

def sort_flag
  @sort_flag
end

#tail ⇒ Object

Returns the value of attribute tail.



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# File 'lib/jif.rb', line 17

def tail
  @tail
end

Instance Method Details

#rebuild(new_file_name = "out.gif") ⇒ Object 



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# File 'lib/jif.rb', line 85

def rebuild(new_file_name="out.gif")
  bit_string = @header
  bit_string += @logical_screen_descriptor
  bit_string += @global_color_table if @global_color_table
  @tail.each do |block|
    if block[:image_descriptor]
      bit_string += image_descriptor_builder block[:image_descriptor]
      bit_string += block[:local_color_table] if block[:local_color_table]
      bit_string += image_data_builder block[:image_data]
    elsif block[:extension_introducer]
      case block[:label]
      when GRAPHICS_CONTROL_EXTENSION_LABEL
        bit_string += graphics_control_extension_builder block
      when PLAIN_TEXT_LABEL, APPLICATION_EXTENSION_LABEL
        bit_string += extension_builder block
      when COMMENT_EXTENSION_LABEL
        bit_string += comment_extension_builder block
      end
    else
      raise "Error: Unknown block header: #{bits[0..7]}"
    end
  end
  File.open(new_file_name, 'wb') do |out|
    out.write [bit_string].pack("B*")
  end
end