Class: FastImage::Gif

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

Overview

:nodoc:

Instance Method Summary collapse

Constructor Details

#initialize(stream) ⇒ Gif

Returns a new instance of Gif.



770
771
772
 
# File 'lib/fastimage.rb', line 770

def initialize(stream)
  @stream = stream
end

Instance Method Details

#animated? ⇒ Boolean

Checks if a delay between frames exists and if it does, then the GIFs is animated

Returns:

  • (Boolean) 


780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
 
# File 'lib/fastimage.rb', line 780

def animated?
  frames = 0

  # "GIF" + version (3) + width (2) + height (2)
  @stream.skip(10)

  # fields (1) + bg color (1) + pixel ratio (1)
  fields = @stream.read(3).unpack("CCC")[0]
  if fields & 0x80 != 0 # Global Color Table
    # 2 * (depth + 1) colors, each occupying 3 bytes (RGB)
    @stream.skip(3 * 2 ** ((fields & 0x7) + 1))
  end

  loop do
    block_type = @stream.read(1).unpack("C")[0]

    if block_type == 0x21 # Graphic Control Extension
      # extension type (1) + size (1)
      size = @stream.read(2).unpack("CC")[1]
      @stream.skip(size)
      skip_sub_blocks
    elsif block_type == 0x2C # Image Descriptor
      frames += 1
      return true if frames > 1

      # left position (2) + top position (2) + width (2) + height (2) + fields (1)
      fields = @stream.read(9).unpack("SSSSC")[4]
      if fields & 0x80 != 0 # Local Color Table
        # 2 * (depth + 1) colors, each occupying 3 bytes (RGB)
        @stream.skip(3 * 2 ** ((fields & 0x7) + 1))
      end

      @stream.skip(1) # LZW min code size (1)
      skip_sub_blocks
    else
      break # unrecognized block
    end
  end

  false
end

#width_and_height ⇒ Object 



774
775
776
 
# File 'lib/fastimage.rb', line 774

def width_and_height
  @stream.read(11)[6..10].unpack('SS')
end