/*
1.26 ClipEar implements the Clipping-Ear-Algorithm.
It finds an "Ear" in this Face, clips it and returns it as separate face.
Note that the original Face is modified by this method!
It is mainly used to implement evaporisation of faces
*/
Face Face::ClipEar() {
Face ret;
if (v.size() <= 3) {
// Nothing to do if this Face consists only of three points
return Face(v);
} else {
Pt a, b, c;
unsigned int n = v.size();
// Go through the corner-points, which are sorted counter-clockwise
for (unsigned int i = 0; i < n; i++) {
// Take the next three points
a = v[(i + 0) % n].s;
b = v[(i + 1) % n].s;
c = v[(i + 2) % n].s;
if (Pt::sign(a, b, c) < 0) {
// If the third point c is right of the segment (a b), then
// the three points don't form an "Ear"
continue;
}
// Otherwise check, if any point is inside the triangle (a b c)
bool inside = false;
for (unsigned int j = 0; j < (n - 3); j++) {
Pt x = v[(i + j + 3) % n].s;
inside = Pt::insideTriangle(a, b, c, x) &&
!(a == x) && !(b == x) && !(c == x);
if (inside) {
// If a point inside was found, we haven't found an ear.
break;
}
}
if (!inside) {
// No point was inside, so build the Ear-Face in "ret",
ret.AddSeg(v[i + 0]);
ret.AddSeg(v[(i + 1)%n]);
Seg nw(v[(i + 1)%n].e, v[i + 0].s);
ret.AddSeg(nw);
// remove the Face-Segment (a b),
v.erase(v.begin() + i);
// and finally replace the segment (b c) by (a c)
v[i].s = nw.e;
v[i].e = nw.s;
hullSeg.valid = 0;
return ret;
}
}
}
DEBUG(2, "No ear found on face " << ToString());
// If we are here it means we haven't found an ear. This shouldn't happen.
// One reason could be that the face wasn't valid in the first place.
return ret;
}
