perf(sleepers): the rails of each track for the fastenings worked out once and kept until its geometry is made again, it goes far or the crossings change, not again for every track laid around it; the fastenings laid only out to 30 m past where they're drawn, the tracks further out keeping their beams to lay them on as they come near; out past 50 m the tracks laid while the laying in a frame took under 2 ms, the rest in the frames after

world/Track.cpp

@@ -1604,6 +1604,7 @@ void TTrack::create_geometry( gfx::geometrybank_handle const &Bank ) {
                     }
                 }
             }
+            track_sleepers::forget_rails( *this );
         }
         auto const lay_rail = [&]( int const Path, gfx::vertex_array const &Profile, int const Side, float const Texturelength, double const From, bool const Openstart, bool const Openend, geometryhandle_sequence &Geometry, geometryhandle_sequence &Cuts ) {
             return this->lay_rail( layout, drawing, Path, Profile, Side, Texturelength, From, Openstart, Openend, Geometry, Cuts ); };