Question

Polygon polygon=new Polygon();
polygon.addPoint(6,4);
polygon.addPoint(25,4);
polygon.addPoint(25,13);
polygon.addPoint(6,13);

我需要知道Point(25,4)中存在的polygon，但

System.out.println(polygon.contains(25,4));

返回false，这个方法似乎只是检查多边形内的Point。

那么，我如何检查已经在多边形中添加的点？

Answer 1

我会使用Polygon.npoints，Polygon.xpoints和Polygon.ypoints来构造hasPoint（Polygon p，int x，int y）方法。

http://docs.oracle.com/javase/7/docs/api/java/awt/Polygon.html

需要对此进行测试，但我想它可能如下所示：

private boolean hasPoint(Polygon p, int x, int y) {
for (int i = 0; i < p.npoints; i++) {
    if (p.xpoints[i] == x && p.ypoints[i] == y)
        return true;
}
return false;
}

Answer 2

假设您无法控制多边形的创建方式，您可以使用PathIterator获取任意Polygon的每个部分。 PathIterator包含有关每个线段起始位置的信息：

import java.awt.*;
import java.awt.geom.*;

class PolygonUtil
{
    public static boolean contains(Polygon polygon, int x, int y)
    {
        if (polygon.contains(x, y))
            return true;

        PathIterator pi = polygon.getPathIterator(null);
        double[] location = new double[6];

        while(! pi.isDone())
        {
            int type = pi.currentSegment(location);
            int piX = (int)location[0];
            int piY = (int)location[1];

            if (x == piX && y == piY)
                return true;

            pi.next();
        }

        return false;
    }

    public static void main(String...args)
    {
        Polygon polygon=new Polygon();
        polygon.addPoint(10, 10);
        polygon.addPoint(30, 10);
        polygon.addPoint(30, 30);
        polygon.addPoint(10, 30);

        // Test 4 corners

        System.out.println("Corners:");
        System.out.println( PolygonUtil2.contains(polygon, 10, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 30) );
        System.out.println( PolygonUtil2.contains(polygon, 10, 30) );

        // Test inside/outside left edge

        System.out.println("Left:");
        System.out.println( PolygonUtil2.contains(polygon, 9, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 10, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 11, 20) );

        // Test inside/outside left edge

        System.out.println("Right:");
        System.out.println( PolygonUtil2.contains(polygon, 29, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 31, 20) );

        // Test above/below top edge

        System.out.println("Top:");
        System.out.println( PolygonUtil2.contains(polygon, 20, 9) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 11) );

        // Test above/below bottom edge

        System.out.println("Bottom:");
        System.out.println( PolygonUtil2.contains(polygon, 20, 29) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 30) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 31) );
    }
}

或者，如果我理解API中找到的definition of insideness，您可以使用：

import java.awt.*;
import java.awt.geom.*;

class PolygonUtil2
{
    public static boolean contains(Polygon polygon, int x, int y)
    {
        System.out.print(x + " : " + y + " - ");

        if (polygon.contains(x, y))
            return true;

        if (polygon.contains(x - 1, y))
            return true;

        if (polygon.contains(x, y - 1))
            return true;

        if (polygon.contains(x - 1, y - 1))
            return true;

        return false;
    }

    public static void main(String...args)
    {
        Polygon polygon=new Polygon();
        polygon.addPoint(10, 10);
        polygon.addPoint(30, 10);
        polygon.addPoint(30, 30);
        polygon.addPoint(10, 30);

        // Test 4 corners

        System.out.println("Corners:");
        System.out.println( PolygonUtil2.contains(polygon, 10, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 30) );
        System.out.println( PolygonUtil2.contains(polygon, 10, 30) );

        // Test inside/outside left edge

        System.out.println("Left:");
        System.out.println( PolygonUtil2.contains(polygon, 9, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 10, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 11, 20) );

        // Test inside/outside left edge

        System.out.println("Right:");
        System.out.println( PolygonUtil2.contains(polygon, 29, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 30, 20) );
        System.out.println( PolygonUtil2.contains(polygon, 31, 20) );

        // Test above/below top edge

        System.out.println("Top:");
        System.out.println( PolygonUtil2.contains(polygon, 20, 9) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 10) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 11) );

        // Test above/below bottom edge

        System.out.println("Bottom:");
        System.out.println( PolygonUtil2.contains(polygon, 20, 29) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 30) );
        System.out.println( PolygonUtil2.contains(polygon, 20, 31) );
    }
}

这两种方法似乎适用于直线水平/垂直线。我会让你测试成角度的线条。

如何检查已经在Polygon中添加的Point？

2 个答案: