Task: Sutherland-Hodgman polygon clipping




Go: package main

import "fmt"

type point struct {
    x, y float32
}

var subjectPolygon = []point{{50, 150}, {200, 50}, {350, 150}, {350, 300},
    {250, 300}, {200, 250}, {150, 350}, {100, 250}, {100, 200}}

var clipPolygon = []point{{100, 100}, {300, 100}, {300, 300}, {100, 300}}

func main() {
    var cp1, cp2, s, e point
    inside := func(p point) bool {
        return (cp2.x-cp1.x)*(p.y-cp1.y) > (cp2.y-cp1.y)*(p.x-cp1.x)
    }
    intersection := func() (p point) {
        dcx, dcy := cp1.x-cp2.x, cp1.y-cp2.y
        dpx, dpy := s.x-e.x, s.y-e.y
        n1 := cp1.x*cp2.y - cp1.y*cp2.x
        n2 := s.x*e.y - s.y*e.x
        n3 := 1 / (dcx*dpy - dcy*dpx)
        p.x = (n1*dpx - n2*dcx) * n3
        p.y = (n1*dpy - n2*dcy) * n3
        return
    }
    outputList := subjectPolygon
    cp1 = clipPolygon[len(clipPolygon)-1]
    for _, cp2 = range clipPolygon { 
        inputList := outputList
        outputList = nil
        s = inputList[len(inputList)-1]
        for _, e = range inputList {
            if inside(e) {
                if !inside(s) {
                    outputList = append(outputList, intersection())
                }
                outputList = append(outputList, e)
            } else if inside(s) {
                outputList = append(outputList, intersection())
            }
            s = e
        }
        cp1 = cp2
    }
    fmt.Println(outputList)
}


Java: import java.awt.*;
import java.awt.geom.Line2D;
import java.util.*;
import java.util.List;
import javax.swing.*;

public class SutherlandHodgman extends JFrame {

    SutherlandHodgmanPanel panel;

    public static void main(String[] args) {
        JFrame f = new SutherlandHodgman();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }

    public SutherlandHodgman() {
        Container content = getContentPane();
        content.setLayout(new BorderLayout());
        panel = new SutherlandHodgmanPanel();
        content.add(panel, BorderLayout.CENTER);
        setTitle("SutherlandHodgman");
        pack();
        setLocationRelativeTo(null);
    }
}

class SutherlandHodgmanPanel extends JPanel {
    List<double[]> subject, clipper, result;

    public SutherlandHodgmanPanel() {
        setPreferredSize(new Dimension(600, 500));

        
        double[][] subjPoints = {{50, 150}, {200, 50}, {350, 150}, {350, 300},
        {250, 300}, {200, 250}, {150, 350}, {100, 250}, {100, 200}};

        double[][] clipPoints = {{100, 100}, {300, 100}, {300, 300}, {100, 300}};

        subject = new ArrayList<>(Arrays.asList(subjPoints));
        result  = new ArrayList<>(subject);
        clipper = new ArrayList<>(Arrays.asList(clipPoints));

        clipPolygon();
    }

    private void clipPolygon() {
        int len = clipper.size();
        for (int i = 0; i < len; i++) {

            int len2 = result.size();
            List<double[]> input = result;
            result = new ArrayList<>(len2);

            double[] A = clipper.get((i + len - 1) % len);
            double[] B = clipper.get(i);

            for (int j = 0; j < len2; j++) {

                double[] P = input.get((j + len2 - 1) % len2);
                double[] Q = input.get(j);

                if (isInside(A, B, Q)) {
                    if (!isInside(A, B, P))
                        result.add(intersection(A, B, P, Q));
                    result.add(Q);
                } else if (isInside(A, B, P))
                    result.add(intersection(A, B, P, Q));
            }
        }
    }

    private boolean isInside(double[] a, double[] b, double[] c) {
        return (a[0] - c[0]) * (b[1] - c[1]) > (a[1] - c[1]) * (b[0] - c[0]);
    }

    private double[] intersection(double[] a, double[] b, double[] p, double[] q) {
        double A1 = b[1] - a[1];
        double B1 = a[0] - b[0];
        double C1 = A1 * a[0] + B1 * a[1];

        double A2 = q[1] - p[1];
        double B2 = p[0] - q[0];
        double C2 = A2 * p[0] + B2 * p[1];

        double det = A1 * B2 - A2 * B1;
        double x = (B2 * C1 - B1 * C2) / det;
        double y = (A1 * C2 - A2 * C1) / det;

        return new double[]{x, y};
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.translate(80, 60);
        g2.setStroke(new BasicStroke(3));
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);

        drawPolygon(g2, subject, Color.blue);
        drawPolygon(g2, clipper, Color.red);
        drawPolygon(g2, result, Color.green);
    }

    private void drawPolygon(Graphics2D g2, List<double[]> points, Color color) {
        g2.setColor(color);
        int len = points.size();
        Line2D line = new Line2D.Double();
        for (int i = 0; i < len; i++) {
            double[] p1 = points.get(i);
            double[] p2 = points.get((i + 1) % len);
            line.setLine(p1[0], p1[1], p2[0], p2[1]);
            g2.draw(line);
        }
    }
}