Java-多边形和线的交点

有没有什么函数可以给我一个交点Polygon and Line2D ?

我有一个多边形和一个我知道相交的线段，我想要交点的实际值而不是布尔答案。

给你。有趣的方法是 getIntersections 和 getIntersection。前者解析所有多边形线段并检查交点，后者进行实际计算。请记住，可以认真优化计算，并且不检查除以 0 的情况。这也仅适用于多边形。如果您引入三次曲线和二次曲线的计算，它可以适应其他形状。假设使用 Line2D.Double 而不是 Line2D.Float。集合用于避免重复点（可能出现在多边形角交叉点上）。

请不要在没有进行广泛测试的情况下使用它，因为我刚刚将其快速组装在一起，并且不确定它是否完全正确。

package quickpolygontest;

import java.awt.Polygon;
import java.awt.geom.Line2D;
import java.awt.geom.PathIterator;
import java.awt.geom.Point2D;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class Main {

    public static void main(String[] args) throws Exception {

        final Polygon poly = new Polygon(new int[]{1,2,2,1}, new int[]{1,1,2,2}, 4);
        final Line2D.Double line = new Line2D.Double(2.5, 1.3, 1.3, 2.5);
        final Set<Point2D> intersections = getIntersections(poly, line);
        for(Iterator<Point2D> it = intersections.iterator(); it.hasNext();) {
            final Point2D point = it.next();
            System.out.println("Intersection: " + point.toString());
        }

    }

    public static Set<Point2D> getIntersections(final Polygon poly, final Line2D.Double line) throws Exception {

        final PathIterator polyIt = poly.getPathIterator(null); //Getting an iterator along the polygon path
        final double[] coords = new double[6]; //Double array with length 6 needed by iterator
        final double[] firstCoords = new double[2]; //First point (needed for closing polygon path)
        final double[] lastCoords = new double[2]; //Previously visited point
        final Set<Point2D> intersections = new HashSet<Point2D>(); //List to hold found intersections
        polyIt.currentSegment(firstCoords); //Getting the first coordinate pair
        lastCoords[0] = firstCoords[0]; //Priming the previous coordinate pair
        lastCoords[1] = firstCoords[1];
        polyIt.next();
        while(!polyIt.isDone()) {
            final int type = polyIt.currentSegment(coords);
            switch(type) {
                case PathIterator.SEG_LINETO : {
                    final Line2D.Double currentLine = new Line2D.Double(lastCoords[0], lastCoords[1], coords[0], coords[1]);
                    if(currentLine.intersectsLine(line))
                        intersections.add(getIntersection(currentLine, line));
                    lastCoords[0] = coords[0];
                    lastCoords[1] = coords[1];
                    break;
                }
                case PathIterator.SEG_CLOSE : {
                    final Line2D.Double currentLine = new Line2D.Double(coords[0], coords[1], firstCoords[0], firstCoords[1]);
                    if(currentLine.intersectsLine(line))
                        intersections.add(getIntersection(currentLine, line));
                    break;
                }
                default : {
                    throw new Exception("Unsupported PathIterator segment type.");
                }
            }
            polyIt.next();
        }
        return intersections;

    }

    public static Point2D getIntersection(final Line2D.Double line1, final Line2D.Double line2) {

        final double x1,y1, x2,y2, x3,y3, x4,y4;
        x1 = line1.x1; y1 = line1.y1; x2 = line1.x2; y2 = line1.y2;
        x3 = line2.x1; y3 = line2.y1; x4 = line2.x2; y4 = line2.y2;
        final double x = (
                (x2 - x1)*(x3*y4 - x4*y3) - (x4 - x3)*(x1*y2 - x2*y1)
                ) /
                (
                (x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4)
                );
        final double y = (
                (y3 - y4)*(x1*y2 - x2*y1) - (y1 - y2)*(x3*y4 - x4*y3)
                ) /
                (
                (x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4)
                );

        return new Point2D.Double(x, y);

    }

}