message: SSAA does not apply to path tracing
  Thus do not clear frame when switching SSAA factor and algorithm is pathtracing
diff: @@ -699,8 +699,11 @@ void renderer::on_key_press(key_event const& event)
  ssaa_samples = 1;
  }
  std::cout << "Use " << ssaa_samples << "x supersampling anti-aliasing\n";
  + if (algo != Pathtracing)
  + {
  counter.reset();
  clear_frame();
  + }
  break;
  case 'u':
  