static std::once_flag flag;
std::call_once(flag, [this]{
global_mixer = new Mixer(QGLFormat::toSurfaceFormat(format()), global_flags.num_cards);
static std::once_flag flag;
std::call_once(flag, [this]{
global_mixer = new Mixer(QGLFormat::toSurfaceFormat(format()), global_flags.num_cards);