Save BMP in Ruby

module Bmp
  def Bmp.save(name, width, height, pixels)
    file = File.open(name,"w")
    bmp_header_size = 14
    dib_header_size = 108
    # BMP header
    file.write("BM")
    pixel_array_size = width * height * 4
    file_size = bmp_header_size + dib_header_size + pixel_array_size
    pixel_array_offset = bmp_header_size + dib_header_size
    bmpHeader = [file_size, 0,0, 0,0, pixel_array_offset]
    file.write(bmpHeader.pack("LCCCCL"))
    # DIB header
    color_planes = 1
    bits_per_pixel = 32
    bi_bitfields = 3
    resolution = 2835
    palette_color_count = 0
    important_color_count = 0
    r = 0x00ff0000
    g = 0x0000ff00
    b = 0x000000ff
    a = 0xff000000
    dibHeader = [
       dib_header_size,
       width,height,color_planes,bits_per_pixel,bi_bitfields,
       pixel_array_size,
       resolution,resolution,
       palette_color_count, important_color_count,
       r,g,b,a]
    file.write(dibHeader.pack("LLLSSLLLLLLLLLL"))
    file.write(" niW")
    file.write("\000"*0x24)
    file.write([0,0,0].pack("LLL"))
    # Pixels
    file.write(pixels.pack("L*"))
    file.close()
  end
end
module Color
  Black = 0xff000000
  White = 0xffffffff
  Transparent = 0x00000000
  Red = 0xffff0000
  Green = 0xff00ff00
  Blue = 0xff0000ff
end
class Canvas
  def initialize(width,height)
    @width = width
    @height = height
    @pixels = Array.new(width*height,Color::Transparent)
  end
  def set_pixel(x,y,color)
    @pixels[x + y*@width] = color
  end
  def save_bmp(name)
      Bmp.save(name,@width,@height,@pixels)
  end
end
canvas = Canvas.new(10,10)
canvas.set_pixel(4,5,Color::Red)
canvas.set_pixel(1,1,Color::White)
canvas.save_bmp("y.bmp")
#save_bmp("x.bmp",3,2,[red,red,red,red,red,red])