You'll want to brush up your trig (or google search like I did ;)). The basic concept is "relatively" easy, but I created a nice method to all the work for me...
This method...
public Point2D getPointOnEdge(float angel, Rectangle bounds) {
float radius = Math.max(bounds.width, bounds.height) / 2;
float x = radius;
float y = radius;
double rads = Math.toRadians((angel + 90));
// Calculate the outter point of the line
float xPosy = (float) (x + Math.cos(rads) * radius);
float yPosy = (float) (y + Math.sin(rads) * radius);
return new Point2D.Float(xPosy + bounds.x, yPosy + bounds.y);
}
Will calculate the x/y point that a given angle will appear on a circle, remember, this will ONLY work for circles!
I then use another method...
public Rectangle2D getActiveBounds(float angel, Rectangle bounds) {
Point2D p = getPointOnEdge(angel, bounds);
return new Rectangle2D.Double(p.getX() - 4, p.getY() - 4, 8, 8);
}
To calculate the "mouse zone" in which I would consider to be the bottom/right area, cause a single pixel is hard to find and simply use Rectangle#contains, passing it the current mouse location...
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Panel;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Path2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Editor {
public static void main(String[] args) {
new Editor();
}
public Editor() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new UMLWindow();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setBounds(30, 30, 1000, 700);
frame.getContentPane().setBackground(Color.white);
frame.setVisible(true);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public static class UMLWindow extends JFrame {
Shapes shapeList = new Shapes();
Panel panel;
private static final long serialVersionUID = 1L;
public UMLWindow() {
addMenus();
panel = new Panel();
}
public void addMenus() {
getContentPane().add(shapeList);
setSize(300, 200);
setLocationRelativeTo(null);
setDefaultCloseOperation(EXIT_ON_CLOSE);
shapeList.addCircle(100, 100);
}
}
// Shapes class, used to draw the shapes on the panel
// as well as implements the MouseListener for dragging
public static class Shapes extends JPanel {
private static final long serialVersionUID = 1L;
private List shapes = new ArrayList();
int currentIndex;
private Point mousePoint;
public Shapes() {
MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
public void addCircle(int width, int height) {
Path2D circ = new Path2D.Double();
circ.append(new Ellipse2D.Double(442, 269, width, height), true);
shapes.add(circ);
repaint();
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setStroke(new BasicStroke(2));
for (Path2D shape : shapes) {
g2.setColor(Color.BLACK);
g2.draw(shape);
g2.setColor(Color.RED);
Rectangle2D bottomRight = getActiveBounds(-45, shape.getBounds());
g2.draw(bottomRight);
if (mousePoint != null) {
if (bottomRight.contains(mousePoint)) {
g2.fill(bottomRight);
}
}
}
}
public Rectangle2D getActiveBounds(float angel, Rectangle bounds) {
Point2D p = getPointOnEdge(angel, bounds);
return new Rectangle2D.Double(p.getX() - 4, p.getY() - 4, 8, 8);
}
public Point2D getPointOnEdge(float angel, Rectangle bounds) {
float radius = Math.max(bounds.width, bounds.height) / 2;
float x = radius;
float y = radius;
double rads = Math.toRadians((angel + 90));
// Calculate the outter point of the line
float xPosy = (float) (x + Math.cos(rads) * radius);
float yPosy = (float) (y + Math.sin(rads) * radius);
return new Point2D.Float(xPosy + bounds.x, yPosy + bounds.y);
}
class MyMouseAdapter extends MouseAdapter {
@Override
public void mouseMoved(MouseEvent e) {
mousePoint = e.getPoint();
repaint();
}
}
}
}
This example does all the work within the paint method, because I wanted to see the "area of effect", you can easily use the same logic to change the mouse cursor within the MouseMoitionListener
