gistfile1.txt

def obj_yrotate(srcobjfile, dstobjfile, amt)
    sinang = Math.sin(amt*Math::PI/180.0)
    cosang = Math.cos(amt*Math::PI/180.0)
    
    fin = File.open(srcobjfile, 'r')
    fout = File.open(dstobjfile, 'w')
    fin.each_line {|line|
        if(line.start_with?('v '))
            v = line.split(' ')[1, 3].map{|x| x.to_f}
            fout.puts "v #{v[0]*cosang + v[2]*sinang} #{v[1]} #{-v[0]*sinang + v[2]*cosang}"
        elsif(line.start_with?('vn '))
            v = line.split(' ')[1, 3].map{|x| x.to_f}
            fout.puts "vn #{v[0]*cosang + v[2]*sinang} #{v[1]} #{-v[0]*sinang + v[2]*cosang}"
        else
            fout.puts line
        end
    }
    fin.close
    fout.close
end

obj_yrotate("testfile.obj", "testfileout90.obj", 90)
obj_yrotate("testfile.obj", "testfileout30.obj", 30)