Module: Tessel::PPM

Defined in:

lib/tessel.rb

Class Method Summary

• .decode(bytes, max_pixels: 16384 * 16384) ⇒ Object
• .encode(image, binary: true) ⇒ Object

Class Method Details

.decode(bytes, max_pixels: 16384 * 16384) ⇒ Object

# File 'lib/tessel.rb', line 699

def decode(bytes, max_pixels: 16384 * 16384)
  bytes = String(bytes).b
  magic = bytes.byteslice(0, 2)
  raise DecodeError, "invalid PPM" unless %w[P3 P6].include?(magic)
  cursor = 2
  token = lambda do
    loop do
      cursor += 1 while cursor < bytes.bytesize && bytes.getbyte(cursor).chr.match?(/\s/)
      if bytes.getbyte(cursor) == 35
        cursor += 1
        cursor += 1 while cursor < bytes.bytesize && bytes.getbyte(cursor) != 10
      else
        break
      end
    end
    start = cursor
    cursor += 1 while cursor < bytes.bytesize && !bytes.getbyte(cursor).chr.match?(/\s/)
    value = bytes.byteslice(start, cursor - start)
    raise DecodeError, "truncated PPM" if value.nil? || value.empty?
    raise DecodeError, "invalid PPM number" unless value.match?(/\A\d+\z/)
    value.to_i
  end
  width, height, max = 3.times.map { token.call }
  raise DecodeError, "invalid PPM dimensions" unless width.positive? && height.positive? && max.between?(1, 65_535)
  raise LimitError, "image exceeds pixel limit" if width * height > max_pixels
  raise DecodeError, "truncated PPM header" if cursor >= bytes.bytesize
  cursor += bytes.byteslice(cursor, 2) == "\r\n" ? 2 : 1
  values = if magic == "P6"
    body = bytes.byteslice(cursor..)
    expected = width * height * 3 * (max < 256 ? 1 : 2)
    raise DecodeError, "invalid PPM pixel data length" unless body.bytesize == expected
    max < 256 ? body.bytes : body.unpack("n*")
  else
    cursor -= 1
    samples = Array.new(width * height * 3) { token.call }
    tail = bytes.byteslice(cursor..)
    raise DecodeError, "extra PPM samples" unless tail.match?(/\A(?:\s+|\#[^\n]*(?:\n|\z))*\z/)
    samples
  end
  raise DecodeError, "PPM sample exceeds maximum" if values.any? { |value| value > max }
  if max != 255
    values.map! { |value| (value * 255.0 / max).round }
  end
  rgba = values.each_slice(3).flat_map { |r, g, b| [r, g, b, 255] }.pack("C*")
  Image.from_rgba(width, height, rgba)
rescue StandardError => e
  raise e if e.is_a?(DecodeError) || e.is_a?(LimitError)
  raise DecodeError, "invalid PPM: #{e.message}"
end

.encode(image, binary: true) ⇒ Object

# File 'lib/tessel.rb', line 690

def encode(image, binary: true)
  rgb = image.to_rgb_bytes
  if binary
    "P6\n#{image.width} #{image.height}\n255\n".b + rgb
  else
    "P3\n#{image.width} #{image.height}\n255\n" + rgb.unpack("C*").each_slice(3).map { |pixel| pixel.join(" ") }.join("\n") + "\n"
  end
end