package com.whyc.util;
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import com.whyc.dto.Point;
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public class PointUtil {
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public static void main(String[] args) {
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int[] x = {0, 8, 8, 0}; // 四边形顶点x坐标
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int[] y = {0, 0, 8, 8}; // 四边形顶点y坐标
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int px = 9, py = 9; // 待检测点坐标
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if (isPointInQuadrilateral(px, py, x, y)) {
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System.out.println("点在四边形内或边上");
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} else {
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System.out.println("点在四边形外");
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}
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}
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/**
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* 判断点是否在四边形内或边上
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* @param px 待测点的x
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* @param py 待测点的y
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* @param x 四个点的x数组 四个点必须是顺时针顺序,从左下角开始顺时针
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* @param y 四个点的y数组
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* @return
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*/
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public static boolean isPointInQuadrilateral(int px, int py, int[] x, int[] y) {
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int n = 4; // 四边形的边数
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// 检查点是否在顶点上
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for (int i = 0; i < n; i++) {
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if (px == x[i] && py == y[i]) {
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return true;
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}
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}
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// 检查点是否在边上
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for (int i = 0; i < n; i++) {
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int j = (i + 1) % n;
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if (isPointOnSegment(px, py, x[i], y[i], x[j], y[j])) {
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return true;
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}
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}
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// 使用射线法判断点是否在凸四边形内
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int intersections = 0;
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for (int i = 0; i < n; i++) {
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int j = (i + 1) % n;
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if (rayIntersectsSegment(px, py, x[i], y[i], x[j], y[j])) {
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intersections++;
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}
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}
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return intersections % 2 != 0;
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}
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private static boolean isPointOnSegment(int px, int py, int x1, int y1, int x2, int y2) {
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// 检查点是否在x1, y1 和 x2, y2 形成的线段上
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if (px < Math.min(x1, x2) || px > Math.max(x1, x2) || py < Math.min(y1, y2) || py > Math.max(y1, y2)) {
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return false;
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}
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// 向量叉积
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int crossProduct = (px - x1) * (y2 - y1) - (py - y1) * (x2 - x1);
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// 向量点积
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int dotProduct1 = (px - x1) * (x2 - x1) + (py - y1) * (y2 - y1);
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int dotProduct2 = (px - x2) * (x1 - x2) + (py - y2) * (y1 - y2);
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return crossProduct == 0 && dotProduct1 >= 0 && dotProduct2 >= 0;
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}
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private static boolean rayIntersectsSegment(int px, int py, int x1, int y1, int x2, int y2) {
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// 确保 y1 <= y2
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if (y1 > y2) {
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return rayIntersectsSegment(px, py, x2, y2, x1, y1);
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}
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// 射线不与线段平行且点在y范围内
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if (py > y1 && py <= y2) {
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// 计算交点x坐标
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//double xIntersection = (double) (px - x1) * (y2 - y1) / (double) (py - y1) + x1;
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double xIntersection = x1 + (double) (py - y1) * (x2 - x1) / (y2 - y1);
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// 射线从左到右，且交点在点的右侧
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return xIntersection >= px;
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}
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return false;
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}
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}
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