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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);
defaultrender.merge=true;
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));
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