Inside clipping with Java Graphics

Question

I need to draw a line using java.awt.Graphics, but only the portion of the line that lies outside of a rectangle should be rendered.

Is it possible to use the Graphics clipping support or do I need to calculate the intersection and clip the line myself?

Answer 1

You need to use the Area class. This example will demonstrate how to do what you ask:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Area;
import java.awt.geom.Rectangle2D;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class Test extends JPanel {

    public static void main(String[] args) {
        JFrame f = new JFrame();
        Test t = new Test();
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(t,BorderLayout.CENTER);
        f.pack();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }

    public Test() {
        setPreferredSize(new Dimension(300, 300));
    }

    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g.create();
        Rectangle2D rectangleNotToDrawIn = new Rectangle2D.Double(100, 100, 20, 30);
        Area outside = calculateRectOutside(rectangleNotToDrawIn);
        g2.setPaint(Color.white);
        g2.fillRect(0, 0, getWidth(), getHeight());
        g2.setPaint(Color.black);
        g2.setClip(outside);
        g2.drawLine(0, 0, getWidth(), getHeight());

    }


    private Area calculateRectOutside(Rectangle2D r) {
        Area outside = new Area(new Rectangle2D.Double(0, 0, getWidth(), getHeight()));
        outside.subtract(new Area(r));
        return outside;
    }

}