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import pointEqual from "../pointEqual";
function Intersection(point, points, other, entry) {
this.x = point;
this.z = points;
this.o = other; // another intersection
this.e = entry; // is an entry?
this.v = false; // visited
this.n = this.p = null; // next & previous
}
// A generalized polygon clipping algorithm: given a polygon that has been cut
// into its visible line segments, and rejoins the segments by interpolating
// along the clip edge.
export default function(segments, compareIntersection, startInside, interpolate, stream) {
var subject = [],
clip = [],
i,
n;
segments.forEach(function(segment) {
if ((n = segment.length - 1) <= 0) return;
var n, p0 = segment[0], p1 = segment[n], x;
// If the first and last points of a segment are coincident, then treat as a
// closed ring. TODO if all rings are closed, then the winding order of the
// exterior ring should be checked.
if (pointEqual(p0, p1)) {
stream.lineStart();
for (i = 0; i < n; ++i) stream.point((p0 = segment[i])[0], p0[1]);
stream.lineEnd();
return;
}
subject.push(x = new Intersection(p0, segment, null, true));
clip.push(x.o = new Intersection(p0, null, x, false));
subject.push(x = new Intersection(p1, segment, null, false));
clip.push(x.o = new Intersection(p1, null, x, true));
});
if (!subject.length) return;
clip.sort(compareIntersection);
link(subject);
link(clip);
for (i = 0, n = clip.length; i < n; ++i) {
clip[i].e = startInside = !startInside;
}
var start = subject[0],
points,
point;
while (1) {
// Find first unvisited intersection.
var current = start,
isSubject = true;
while (current.v) if ((current = current.n) === start) return;
points = current.z;
stream.lineStart();
do {
current.v = current.o.v = true;
if (current.e) {
if (isSubject) {
for (i = 0, n = points.length; i < n; ++i) stream.point((point = points[i])[0], point[1]);
} else {
interpolate(current.x, current.n.x, 1, stream);
}
current = current.n;
} else {
if (isSubject) {
points = current.p.z;
for (i = points.length - 1; i >= 0; --i) stream.point((point = points[i])[0], point[1]);
} else {
interpolate(current.x, current.p.x, -1, stream);
}
current = current.p;
}
current = current.o;
points = current.z;
isSubject = !isSubject;
} while (!current.v);
stream.lineEnd();
}
}
function link(array) {
if (!(n = array.length)) return;
var n,
i = 0,
a = array[0],
b;
while (++i < n) {
a.n = b = array[i];
b.p = a;
a = b;
}
a.n = b = array[0];
b.p = a;
}
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