Command line quickie to convert binary .3ds files and output ascii .obj file. Materials are ignored.

3ds2obj.rb

v_tot = 1
vqty = 0

file = ARGV.shift
f = File.new(file, "rb")

while ! f.eof?
  cid = f.read(2).unpack('s')[0] 
  len = f.read(4).unpack('i')[0]
  #puts "# len=#{ len.inspect }"
  case cid
  when 0x4d4d
    puts "# MAIN CHUNK"
    next

  when 0x3d3d
    puts "#  3D EDITOR CHUNK"
    next

  when 0x4000
    puts "#   OBJECT BLOCK : "
    name = ""
    20.times do 
      c = f.read(1)
      break if c == "\000"
      c =  c.unpack('C')[0].chr
      name << c
    end
    puts "g #{name}"
    next

  when 0x4100
    next

  when 0x4110
    print "#     VERTICES LIST: "
    vqty = f.read(2).unpack('s')[0]
    puts "(#{ vqty.inspect })"
    vqty.times do 
      x = f.read(4).unpack('f')[0]
      y = f.read(4).unpack('f')[0]
      z = f.read(4).unpack('f')[0]
      str = "v #{x} #{y} #{z}"
      #print v_tot," "
      puts str
      v_tot += 1
    end
    next

  when 0x4120
    print "#  FACES"
    qty = f.read(2).unpack('s')[0]
    puts "(#{ qty.inspect })"
    qty.times do 
      a = f.read(2).unpack('s')[0]
      b = f.read(2).unpack('s')[0]
      c = f.read(2).unpack('s')[0]
      flags = f.read(2).unpack('s')[0]
      str =  "f #{v_tot-vqty+a} #{v_tot-vqty+b} #{v_tot-vqty+c}"
      puts str
    end
    next

  else
    f.seek(len-6, IO::SEEK_CUR)
  end

end

f.close