module ChunkyPNG::Canvas::PNGDecoding

def decode_png_pixelstream(stream, width, height, color_mode = ChunkyPNG::COLOR_TRUECOLOR, palette = nil, interlace = ChunkyPNG::INTERLACING_NONE)
  raise "This palette is not suitable for decoding!" if palette && !palette.can_decode?
  pixel_size    = Color.bytesize(color_mode)
  pixel_decoder = case color_mode
    when ChunkyPNG::COLOR_TRUECOLOR       then lambda { |bytes| ChunkyPNG::Color.rgb(*bytes) }
    when ChunkyPNG::COLOR_TRUECOLOR_ALPHA then lambda { |bytes| ChunkyPNG::Color.rgba(*bytes) }
    when ChunkyPNG::COLOR_INDEXED         then lambda { |bytes| palette[bytes.first] }
    when ChunkyPNG::COLOR_GRAYSCALE       then lambda { |bytes| ChunkyPNG::Color.grayscale(*bytes) }
    when ChunkyPNG::COLOR_GRAYSCALE_ALPHA then lambda { |bytes| ChunkyPNG::Color.grayscale(*bytes) }
    else raise "No suitable pixel decoder found for color mode #{color_mode}!"
  end
  return case interlace
    when ChunkyPNG::INTERLACING_NONE  then decode_png_without_interlacing(stream, width, height, pixel_size, pixel_decoder)
    when ChunkyPNG::INTERLACING_ADAM7 then decode_png_with_adam7_interlacing(stream, width, height, pixel_size, pixel_decoder)
    else raise "Don't know how the handle interlacing method #{interlace}!"
  end
end