I want to redraw my oval as the mouse enters it-CodePudding

public void mouseEntered(MouseEvent e) {
        int x = e.getX();
        int y = e.getY();
        m_View = new View(m_Mod);
        int maxY = m_Mod.y1   m_Mod.oheight;
        int maxX = m_Mod.x1   m_Mod.owidth;
        if (x > m_Mod.x1 & x < maxX & y > m_Mod.y1 & x < maxY) {
            Graphics g = m_Mod.frame.getGraphics();
            m_View.draw(g);
            System.out.print("IM KREIS");
        }
    }

Somehow my math does not work here. I want to redraw my oval as soon as the mouse enters it. So my graphics object "g" is my oval here. m_Mod.x1 / M_Mod.y1 is x and y of my oval and m_Mod.width / m_Mod.heigth are width and heigth of my oval.

CodePudding user response：

As mentioned in comments, the key to a solution is to:

Do all drawing, all graphics and mouse listening within a single drawing JPanel
To specifically draw within the JPanel's paintComponent method override
To give your GUI a boolean field that is set to true
To use an Ellipse2D object to define your oval
To add a MouseMotionListener to the drawing JPanel
Within this MouseMotionListener, check if the mouse point is within the ellipse
Then set the boolean field with this result and call repaint()
The paintComponent method will then determine what to draw based on the state of the boolean

For example, in the code below I have an Ellise2D field,

private Ellipse2D myOval = new Ellipse2D.Double(OVAL_X, OVAL_Y, OVAL_W, OVAL_H);

Then there is a boolean field, private boolean insideOval = false; that is set to false and that is changed within a MouseMotionListener to true if the mouse point is within the ellpise (here called myOval):

addMouseMotionListener(new MouseAdapter() {         
    @Override
    public void mouseMoved(MouseEvent e) {
        
        // true if the mouse point is within the oval. Otherwise false
        insideOval = myOval.contains(e.getPoint());
        
        // redraw the JPanel to draw the state of insideOval
        repaint();
    }
});

Then the paintComponent method will use the state of insideOval to determine what color to fill the oval with, an "active color" if the boolean is true and a clear color if not:

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g); // does house-keeping drawing
    Graphics2D g2 = (Graphics2D)g;
    // allow for smooth curves
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    
    // vary the oval fill color depending on the state of the insideOval field
    Color c = insideOval ? ACTIVE_COLOR : INACTIVE_COLOR;
    g2.setColor(c);
    
    // fill the oval
    g2.fill(myOval);
    
    // then draw the oval's border
    g2.setColor(OVAL_BORDER);
    g2.setStroke(BORDER_STROKE);
    g2.draw(myOval);
}

For example:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Stroke;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;

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

@SuppressWarnings("serial")
public class DrawingPanel extends JPanel {
    // main JPanel dimensions
    private static final int PREF_W = 600;
    private static final int PREF_H = 600;
    
    // oval dimensions
    private static final double OVAL_X = 100;
    private static final double OVAL_Y = OVAL_X;
    private static final double OVAL_W = 400;
    private static final double OVAL_H = OVAL_W;
    
    // oval colors
    private static final Color INACTIVE_COLOR = new Color(0, 0, 0, 0); // clear
    private static final Color ACTIVE_COLOR = Color.PINK;
    private static final Color OVAL_BORDER = Color.LIGHT_GRAY;
    
    // thickness of mouse border
    private static final Stroke BORDER_STROKE = new BasicStroke(4f);
    
    // Oval to draw and boolean to tell if mouse within the oval
    private Ellipse2D myOval = new Ellipse2D.Double(OVAL_X, OVAL_Y, OVAL_W, OVAL_H);
    private boolean insideOval = false;
    
    public DrawingPanel() {
        // add a mouse motion listener to this same drawing JPanel
        // and inside of it, check if the mouse point is inside or outside
        // of the oval.
        addMouseMotionListener(new MouseAdapter() {         
            @Override
            public void mouseMoved(MouseEvent e) {
                
                // true if the mouse point is within the oval. Otherwise false
                insideOval = myOval.contains(e.getPoint());
                
                // redraw the JPanel to draw the state of insideOval
                repaint();
            }
        });
    }
    
    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return getPreferredSize();
        } else {
            return new Dimension(PREF_W, PREF_H);
        }
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g); // does house-keeping drawing
        Graphics2D g2 = (Graphics2D)g;
        // allow for smooth curves
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        
        // vary the oval fill color depending on the state of the insideOval field
        Color c = insideOval ? ACTIVE_COLOR : INACTIVE_COLOR;
        g2.setColor(c);
        
        // fill the oval
        g2.fill(myOval);
        
        // then draw the oval's border
        g2.setColor(OVAL_BORDER);
        g2.setStroke(BORDER_STROKE);
        g2.draw(myOval);
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            DrawingPanel mainPanel = new DrawingPanel();

            JFrame frame = new JFrame("GUI");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(mainPanel);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }

}