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.


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# File 'lib/fastimage.rb', line 570

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)

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# File 'lib/fastimage.rb', line 580

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 # 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_heightObject


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# File 'lib/fastimage.rb', line 574

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