perf(sleepers): the instances of the sleepers and timbers of a track sent to the gpu once, as it's laid, and kept there in a buffer of their own; in each pass the runs of them in sight turned by the modelviews of their cells into the instance buffer of the frame by a compute pass, one dispatch and one barrier a pass, and drawn in one instanced draw for each model, part and level of detail, in place of the cpu turning every instance every frame

world/TrackSleepers.h

@@ -103,6 +103,7 @@ struct laid {
     std::vector<glm::mat4> whole; // transforms of the timbers of a model without parts, drawn whole
     std::vector<glm::mat4> plain; // transforms of the plain sleepers, whole models, relative to the origin of the track
     std::vector<chunk> chunks;
+    std::uint64_t made { 0 }; // which making of the instances they are, none other of any track the same: a copy of them tells by it
     bool fastened { false }; // the fastenings are laid, else they're laid as the track comes near where they're drawn
     std::vector<beam> beams; // kept for the fastenings till they're laid
 };