/*
* Split the polygon in two, by the given line. Returns a list of polygons. The first is the one who contains the
* given point.
*/
public ArrayList<Polygon> getSplits(Point2D pointOnLeftSide, Line2D splitLine) {
PointRing left = new PointRing();
PointRing right = new PointRing();
PointRing actual = left;
// we check if the given point is valid for this polygon
if (!points.contains(pointOnLeftSide))
throw new RuntimeException("The specified point can't be found in this polygon.");
Point2D p = pointOnLeftSide;
Point2D start = null;
// TODO, gerer les splits sur un point unique
for (int i = 0; i < size(); i++) {
actual.add(p);
Point2D next = points.getNext(p);
Segment2D edge = new Segment2D(p, next);
if (edge.isCollinear(splitLine))
throw new RuntimeException(
"Trying to split a polygon with a line collinear to one of its edges : " + splitLine);
if (edge.intersect(splitLine)) {
// An intersection point is found
Point2D intersection = edge.getAnyIntersection(splitLine);
// We check if the intersection point is the end of the edge.
// In this case, we continue to the next edge which will have intersection on its start
// point.
if (!intersection.equals(edge.getEnd())) {
// We check if the intersection is on the edge start.
// In this case, we don't add the point to the actual polygon
if (!intersection.equals(edge.getStart())) actual.add(intersection);
// then we switch actual polygon
if (actual == left) {
// we save the point just before the intersection. after the split, we will shift the
// left
// polygon to this point.
start = p;
actual = right;
} else actual = left;
// after switching, we add the intersection to the new actual polygon.
actual.add(intersection);
}
}
p = next;
}
// debug : check if we get only one intersection
if (actual == right)
throw new RuntimeException(
"The polygon have been splitted on an impair number of points, which is not allowed.");
left.shiftTo(start);
ArrayList<Polygon> res = new ArrayList<Polygon>();
res.add(new Polygon(left));
res.add(new Polygon(right));
return res;
}
