+void Gear::attach(Gear *g)
+{
+ if(g->supergear) {
+ if(g->supergear == this) {
+ return;
+ }
+ g->supergear->detach(g);
+ }
+ g->supergear = this;
+ subgears.push_back(g);
+
+ // make co-axial
+ g->axis = axis;
+ g->pos.x = pos.x;
+ g->pos.y = pos.y;
+}
+
+bool Gear::detach(Gear *g)
+{
+ int nsubgears = (int)subgears.size();
+ for(int i=0; i<nsubgears; i++) {
+ if(subgears[i] == g) {
+ subgears.erase(subgears.begin() + i);
+ g->supergear = 0;
+ return true;
+ }
+ }
+ return false;
+}
+
+Gear *Gear::get_super() const
+{
+ return supergear;
+}
+