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/SleeperRules.h

@@ -87,6 +87,12 @@ double constexpr pad_narrowest { 0.02 };
 double constexpr fastening_overlap { 0.01 };
 // how far from the camera the fastenings are drawn at most
 double constexpr fastening_range { 120.0 };
+// how much further out the fastenings are laid, there as the camera comes near
+double constexpr fastening_lead { 30.0 };
+// how near the camera the beams of a track are laid at once as they're needed; further out while the laying in a frame took less
+// than the budget, in ms, the rest left for the frames after
+double constexpr lay_near { 50.0 };
+double constexpr lay_budget { 2.0 };
 
 // how many tracks a cluster takes at most
 std::size_t constexpr cluster_cap { 256 };