STL.rb

class STL
  class Writer
    attr_accessor :tris, :size
    def initialize tris
      @tris = tris
      @size = tris.length*50 + 80 + 4
    end

    def write_stl_header f
      80.times {|n| f << [0].pack("C") } #uint8
    end

    def write_number_tris f
      f << [@size].pack("L") #uint32
    end

    def write_tris f
      @tris.each do |t|
        f << [0,0,0].pack("fff")    # normals, dont matter
        f << t[0].values.pack("fff")  # 3 vertices
        f << t[1].values.pack("fff")
        f << t[2].values.pack("fff")
        f << [0].pack("S")      # random uint16 at the end of each tri
      end
    end

    def save_as fname
      File.open(fname, "wb") do |f|
        write_stl_header(f)
        write_number_tris(f)
        write_tris(f)
      end
    end

  end
end