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56 lines
1.5 KiB
Java
56 lines
1.5 KiB
Java
import java.util.*;
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public class ConvexCut {
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public static class Point {
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public double x, y;
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public Point(double x, double y) {
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this.x = x;
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this.y = y;
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}
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}
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// cuts right part of poly (returns left part)
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public static Point[] convexCut(Point[] poly, Point p1, Point p2) {
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int n = poly.length;
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List<Point> res = new ArrayList<>();
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for (int i = 0, j = n - 1; i < n; j = i++) {
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int d1 = orientation(p1.x, p1.y, p2.x, p2.y, poly[j].x, poly[j].y);
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int d2 = orientation(p1.x, p1.y, p2.x, p2.y, poly[i].x, poly[i].y);
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if (d1 >= 0)
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res.add(poly[j]);
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if (d1 * d2 < 0)
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res.add(getLinesIntersection(p1.x, p1.y, p2.x, p2.y, poly[j].x, poly[j].y, poly[i].x, poly[i].y));
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}
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return res.toArray(new Point[res.size()]);
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}
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static int orientation(double ax, double ay, double bx, double by, double cx, double cy) {
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bx -= ax;
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by -= ay;
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cx -= ax;
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cy -= ay;
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double cross = bx * cy - by * cx;
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double EPS = 1e-9;
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return cross < -EPS ? -1 : cross > EPS ? 1 : 0;
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}
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static Point getLinesIntersection(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
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double a1 = y2 - y1;
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double b1 = x1 - x2;
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double c1 = -(x1 * y2 - x2 * y1);
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double a2 = y4 - y3;
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double b2 = x3 - x4;
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double c2 = -(x3 * y4 - x4 * y3);
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double det = a1 * b2 - a2 * b1;
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double x = -(c1 * b2 - c2 * b1) / det;
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double y = -(a1 * c2 - a2 * c1) / det;
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return new Point(x, y);
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}
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public static void main(String[] args) {
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}
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}
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