import three;

size(300);

// A structure to subdivide two intersecting patches about their intersection.
struct split
{
 surface[] S={new surface};
 surface[] T={new surface};

 struct tree {
   tree[] tree=new tree[2];
 }
 // Default subdivision depth.
 int n=20;

 // Subdivide p and q to depth n if they overlap.
 void write(tree pt, tree qt, triple[][] p, triple[][] q, int depth=n) {
   --depth;
   triple[][][] Split(triple[][] P, real u=0)=depth % 2 == 0 ? hsplit : vsplit;
   triple[][][] P=Split(p);
   triple[][][] Q=Split(q);

   for(int i=0; i < 2; ++i) {
     triple[][] Pi=P[i];
     for(int j=0; j < 2; ++j) {
       triple[][] Qj=Q[j];
       if(overlap(Pi,Qj)) {
         if(!pt.tree.initialized(i))
           pt.tree[i]=new tree;
         if(!qt.tree.initialized(j))
           qt.tree[j]=new tree;
         if(depth > 0)
           write(pt.tree[i],qt.tree[j],Pi,Qj,depth);
       }
     }
   }
 }

 // Output the subpatches of p from subdivision.
 void read(surface[] S, tree t, triple[][] p, int depth=n) {
   --depth;
   triple[][][] Split(triple[][] P, real u=0)=depth % 2 == 0 ? hsplit : vsplit;
   triple[][][] P=Split(p);

   for(int i=0; i < 2; ++i) {
     if(t.tree.initialized(i))
       read(S,t.tree[i],P[i],depth);
     else {
       S[0].push(patch(P[i]));
     }
   }
 }

 void operator init(triple[][] p, triple[][] q, int depth=n) {
   tree ptrunk,qtrunk;
   write(ptrunk,qtrunk,p,q,depth);
   read(T,ptrunk,p,depth);
   read(S,qtrunk,q,depth);
 }
}

currentprojection=orthographic(0,0,1);

triple[][] A=
 {
  {(0,0,0),(1,0,0),(1,0,0),(2,0,0)},
  {(0,4/3,0),(2/3,4/3,2),(4/3,4/3,2),(2,4/3,0)},
  {(0,2/3,0),(2/3,2/3,0),(4/3,2/3,0),(2,2/3,0)},
  {(0,2,0),(2/3,2,0),(4/3,2,0),(2,2,0)}
 };

triple[][] B=
 {
  {(0.5,0,-1),(0.5,1,-1),(0.5,2,-1),(0.5,3,-1)},
  {(0.5,0,0),(0.5,1,0),(0.5,2,0),(0.5,3,0)},
  {(0.5,0,1),(0.5,1,1),(0.5,2,1),(0.5,3,1)},
  {(0.5,0,2),(0.5,1,2),(0.5,2,2),(0.5,3,2)}
 };

split S=split(B,A);

for(int i=0; i < S.S[0].s.length; ++i)
 draw(surface(S.S[0].s[i]),Pen(i));

for(int i=0; i < S.T[0].s.length; ++i)
 draw(surface(S.T[0].s[i]),Pen(i));