Show a line between first mouse click and cursor-CodePudding

I'm trying to write a program that will show a line between the first click and mouse position after the 1st click. Then after the 2nd click, it shows a line.

I know I will have to use MouseListener getX(), getY() to get the position where the mouse click is at, but the part where I am confused is to show a line between the first click and mouse position then after the second click it shows a line. The tutorial I found online only show me how to draw a line between two mouse clicks.

Would greatly appreciate if anyone can point me in the right direction.

CodePudding user response：

You need to know three points.

First click point
Second click point
The current mouse point

If both first and second click points are null, then basically do nothing

If the first click point and current mouse point are not null and the second point is null, draw a line between the first and transient point

If both the first and second click points are not null, then draw a line between those two instead

To make this work, you'll need a MouseListener and a MouseMotionListener

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Point startPoint;
        private Point endPoint;
        private Point transientPoint;

        public TestPane() {
            MouseAdapter ma = new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {
                    if (startPoint == null) {
                        startPoint = e.getPoint();
                    } else if (endPoint == null) {
                        endPoint = e.getPoint();
                    } else {
                        endPoint = null;
                        startPoint = e.getPoint();
                    }
                    repaint();
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                    if (startPoint != null && endPoint == null) {
                        transientPoint = e.getPoint();
                        repaint();
                    } else {
                        transientPoint = null;
                    }
                }
            };

            addMouseListener(ma);
            addMouseMotionListener(ma);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (startPoint != null && endPoint != null) {
                g2d.setColor(Color.BLUE);
                g2d.draw(new Line2D.Double(startPoint, endPoint));
            } else if (startPoint != null && transientPoint != null) {
                g2d.setColor(Color.RED);
                g2d.draw(new Line2D.Double(startPoint, transientPoint));
            }
            g2d.dispose();
        }

    }
}