Get the corners of a rotating rectangle

Question

I have a rectangle that rotates around it, and I have another rectangle that I want to connect to the upper right corner of the rotating rectangle. The problem is that I have no idea how to get the corner so that the second rectangle always gets stuck in that corner.

This is my sample code. Right now, the second rectangle will be in the same place all the time, which is not the result of what I need.

package Test; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; import javax.swing.*; class Test{ public static void main(String[] args){ new Test(); } public Test(){ EventQueue.invokeLater(new Runnable() { @Override public void run() { JFrame frame = new JFrame("Test"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new Graphic()); frame.setSize(1000,700); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } } class Graphic extends JPanel{ private int x, y, windowW, windowH; private double angle; private Rectangle rect1, rect2; private Path2D path; private Timer timer; private AffineTransform rotation; public Graphic(){ windowW = (int) Toolkit.getDefaultToolkit().getScreenSize().getWidth(); windowH = (int) Toolkit.getDefaultToolkit().getScreenSize().getHeight(); path = new Path2D.Double(); rotation = new AffineTransform(); angle = 0; x = windowW / 2; y = windowH / 2; timer = new Timer(100, new ActionListener(){ @Override public void actionPerformed(ActionEvent e){ angle += .1; if(angle > 360) angle -= 360; repaint(); } }); timer.start(); } @Override public void paintComponent(Graphics g){ super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; rotation.setToTranslation(500, 200); rotation.rotate(angle, 32, 32); rect1 = new Rectangle(0, 0, 64, 64); path = new Path2D.Double(rect1, rotation); rect2 = new Rectangle(path.getBounds().x, path.getBounds().y, 10, 50); g2d.fill(path); g2d.fill(rect2); } } 

Answer 1

The mathematical solution :)

 public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; rotation.setToTranslation(500, 200); rotation.rotate(angle, 32, 32); rect1 = new Rectangle(0, 0, 64, 64); path = new Path2D.Double(rect1, rotation); double r = 32.0 * Math.sqrt(2); // (532, 232) - coordinates of rectangle center | // you can change position of second rectangle by this V substraction (all you need to know is that the full circle corresponds to 2Pi) int x2 = (int) Math.round(532 + r * Math.cos(angle - Math.PI / 4)); int y2 = (int) Math.round(232 + r * Math.sin(angle - Math.PI / 4)); rect2 = new Rectangle(x2, y2, 10, 50); g2d.fill(path); g2d.fill(rect2); } 

Of course, some constants must be class fields, not method variables.

Answer 2

I cannot verify this code, but I believe that this is the correct working code that you want

 int hw = -width / 2; int hh = -height / 2; int cos = Math.cos( theta ); int sin = Math.sin( theta ); int x = hw * cos - hh * sin; int y = hw * sin + hh * cos; 

This will give you the upper left corner based on the theta, the rotation of the square. To get other angles, you simply use changes in the values ​​of hw and hh:

 //top right corner hw = width / 2 hh = -height / 2 //bottom right corner hw = width / 2 hh = height / 2 //bottom left corer hw = -width / 2 hh = height / 2 

I hope this helps