static int edgesIntersect(Point * P, Point * Q, int n, int m)
{
int a = 0;
int b = 0;
int aa = 0;
int ba = 0;
int a1, b1;
Point A, B;
double cross;
int bHA, aHB;
Point p;
int inflag = Unknown;
/* int i = 0; */
/* int Reset = 0; */
do {
a1 = (a + n - 1) % n;
b1 = (b + m - 1) % m;
subpt(&A, P[a], P[a1]);
subpt(&B, Q[b], Q[b1]);
cross = area_2(origin, A, B);
bHA = leftOf(P[a1], P[a], Q[b]);
aHB = leftOf(Q[b1], Q[b], P[a]);
/* If A & B intersect, update inflag. */
if (intersection(P[a1], P[a], Q[b1], Q[b], &p))
return 1;
/* Advance rules. */
if ((cross == 0) && !bHA && !aHB) {
if (inflag == Pin)
advance(b, ba, m);
else
advance(a, aa, n);
} else if (cross >= 0)
if (bHA)
advance(a, aa, n);
else {
advance(b, ba, m);
} else { /* if ( cross < 0 ) */
if (aHB)
advance(b, ba, m);
else
advance(a, aa, n);
}
} while (((aa < n) || (ba < m)) && (aa < 2 * n) && (ba < 2 * m));
return 0;
}
/* Intersection area */
template<class K> typename K::FT intersection_area_two_slabs(const Rectangle_2<K>& a, const Rectangle_2<K> &b) {
typedef typename K::Vector_2 Vector_2;
typedef typename K::Line_2 Line_2;
typedef typename K::Point_2 Point_2;
typedef typename K::FT FT;
Origin O;
if(a.is_degenerate() || b.is_degenerate()) return 0;
std::vector<Vector_2> v;
std::vector<Line_2> l;
for(unsigned int i=0; i<4; ++i) { v.push_back(b[i]-O); l.push_back(b.line(i)); }
const Vector_2& n = a.normal();
FT r = a.ratio();
FT n2 = n.squared_length();
FT rn2 = r*r*n2;
Vector_2 vc(a.center()-O);
Vector_2 trn(-r*n.y(),r*n.x());
FT ctrn = vc*trn;
FT cn = vc*n;
Vector_2 ln[] = { n, trn };
FT lc[] = { cn+n2, ctrn+rn2, cn-n2, ctrn-rn2 };
// basically it is the iterative intersection of the convex polygon initialized with b
// with the 2 slabs line0/line2 and line1/line3.
for(unsigned int i=0; i<2; ++i) {
int begin0=-1, end0=-1;
int begin1=-1, end1=-1;
unsigned int n=v.size();
for(unsigned int j=0; j<n; ++j) {
FT dot = ln[i]*v[j];
if( dot>lc[i]) {
if(end0==-1 && begin0!=-1) end0=j;
if(begin1<=end1) begin1=j;
} else {
if(begin0<=end0) begin0=j;
if(dot<lc[i+2]) {
if(end1==-1 && begin1!=-1) end1=j;
} else {
if(begin1<=end1) begin1=j;
}
}
}
if(begin0==-1 || begin1==-1 ) return 0; // outside the slab
if(end0 ==-1) {
if(begin0!=0) end0=0;
else begin0=begin1;
}
if(end1 ==-1) {
if(begin1!=0) end1=0;
else {
if(end0==-1) continue; // inside the slab
begin1=begin0;
}
}
std::vector<Vector_2> w;
std::vector<Line_2> m;
if(end0!=-1) { // cut outside line(i+1)
for(int j=begin1; j!=end0; j=(j+1)%n) {
w.push_back(v[j]);
m.push_back(l[j]);
}
Point_2 inter(O);
Line_2 li(ln[i].x(),ln[i].y(),-lc[i]);
intersection(l[(end0+n-1)%n],li).assign(inter);
w.push_back(inter-O);
m.push_back(li);
m.push_back(l[(begin0+n-1)%n]);
intersection(li,m.back()).assign(inter);
w.push_back(inter-O);
}
if(end1!=-1) { // cut outside line(i+3)
for(int j=begin0; j!=end1; j=(j+1)%n) {
w.push_back(v[j]);
m.push_back(l[j]);
}
Point_2 inter(O);
Line_2 li(ln[i].x(),ln[i].y(),-lc[i+2]);
intersection(l[(end1+n-1)%n],li).assign(inter);
w.push_back(inter-O);
m.push_back(li);
m.push_back(l[(begin1+n-1)%n]);
intersection(li,m.back()).assign(inter);
w.push_back(inter-O);
}
std::swap(v,w);
std::swap(l,m);
}
std::vector<Point_2> p;
for(unsigned int i=0; i<v.size(); ++i) { p.push_back(O+v[i]); }
FT area;
area_2(p.begin(),p.end(),area);
return abs(area);
}
