ru:: ferris platforms have period and can be last_platform

rogueviz/ru/classes.cpp

@@ -485,6 +485,7 @@ struct moving_platform : public entity {
   };
 
 struct ferris_platform : public moving_platform {
+  ld period;
   xy location_at(ld t) override;
   string get_name() override { return "Ferris platform"; }
   string get_help() override { return "Ferris wheel platforms, powered by some ancient mechanism. They always go in perfect circles, with constant velocity."; }

rogueviz/ru/entity.cpp

@@ -626,7 +626,7 @@ void avoid::act() {
   }
 
 xy ferris_platform::location_at(ld t) {
-  return from_hyper(rgpushxto0(to_hyper(ctr)) * xspinpush0(t / game_fps + shift, radius));
+  return from_hyper(rgpushxto0(to_hyper(ctr)) * xspinpush0(t / game_fps / period * TAU + shift, radius));
   }
 
 xy rope_platform::location_at(ld t) {

rogueviz/ru/load-world.cpp

@@ -317,12 +317,16 @@ void load_room(fhstream& f, cell *c) {
         r.entities.emplace_back(std::move(b));
         }
       else if(cap == "FERRIS") {
-        ld cx = get_ld(), cy = get_ld(), radius = get_ld(); int qty = get_int();
+        ld cx = get_ld(), cy = get_ld(), radius = get_ld(); int qty = get_int(); ld period = get_ld();
+
+        last_platform = {};
 
         for(int i=0; i<qty; i++) {
           auto b = std::make_unique<ferris_platform>();
           b->ctr = {cx, cy}; b->radius = radius;
           b->shift = i * TAU / qty;
+          b->period = period;
+          last_platform.push_back(&*b);
           r.entities.emplace_back(std::move(b));
           }
         }