split Polygon - Java 2D Graphics

Java examples for 2D Graphics:Polygon

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Description

split Polygon

Demo Code


//package com.java2s;
import java.awt.Point;
import java.awt.Polygon;

public class Main {
    public static Polygon[] splitPolygon(Polygon p, int l1x1, int l1y1,
            int l1x2, int l1y2) {
        Polygon[] newPolygons = new Polygon[2];

        Polygon firstPolygon = new Polygon();
        Polygon secondPolygon = new Polygon();
        int firstEdge = -1;
        int secondEdge = -1;
        Point firstPoint = null;/*w  ww .  j a  v a  2 s .co m*/
        Point secondPoint = null;
        int edge = 0;
        while (true) {
            if (edge >= p.npoints)
                edge = 0;
            int i = edge;
            int j = i == p.npoints - 1 ? 0 : i + 1;
            int l2x1 = p.xpoints[i];
            int l2x2 = p.xpoints[j];
            int l2y1 = p.ypoints[i];
            int l2y2 = p.ypoints[j];
            Point intersect = getIntersection(l1x1, l1y1, l1x2, l1y2, l2x1,
                    l2y1, l2x2, l2y2);
            if (intersect != null) {
                if (firstEdge == -1) {
                    firstEdge = i;
                    firstPoint = intersect;
                    firstPolygon.addPoint(firstPoint.x, firstPoint.y);
                    firstPolygon.addPoint(l2x2, l2y2);
                } else if (secondEdge == -1) {
                    secondEdge = i;
                    secondPoint = intersect;
                    firstPolygon.addPoint(intersect.x, intersect.y);
                    firstPolygon.addPoint(firstPoint.x, firstPoint.y);
                    secondPolygon.addPoint(secondPoint.x, secondPoint.y);
                    secondPolygon.addPoint(l2x2, l2y2);
                } else if (secondEdge > -1) {
                    secondPolygon.addPoint(intersect.x, intersect.y);
                    secondPolygon.addPoint(secondPoint.x, secondPoint.y);
                    break;
                }
            } else {
                if (firstEdge > -1 && secondEdge == -1)
                    firstPolygon.addPoint(l2x2, l2y2);
                else if (secondEdge > -1 && secondEdge > -1)
                    secondPolygon.addPoint(l2x2, l2y2);
            }
            edge++;
        }

        newPolygons[0] = firstPolygon;
        newPolygons[1] = secondPolygon;

        return newPolygons;
    }

    public static Point getIntersection(int l1x1, int l1y1, int l1x2,
            int l1y2, int l2x1, int l2y1, int l2x2, int l2y2) {
        double d = (l2y2 - l2y1) * (l1x2 - l1x1) - (l2x2 - l2x1)
                * (l1y2 - l1y1);
        double na = (l2x2 - l2x1) * (l1y1 - l2y1) - (l2y2 - l2y1)
                * (l1x1 - l2x1);
        double nb = (l1x2 - l1x1) * (l1y1 - l2y1) - (l1y2 - l1y1)
                * (l1x1 - l2x1);
        if (d == 0D)
            return null;

        double ua = na / d;
        double ub = nb / d;
        if (ua >= 0D && ua <= 1D && ub >= 0D && ub <= 1D) {
            Point intersect = new Point();
            intersect.x = (int) (l1x1 + (ua * (l1x2 - l1x1)));
            intersect.y = (int) (l1y1 + (ua * (l1y2 - l1y1)));
            return intersect;
        }

        return null;
    }
}

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