java.awt.Graphics绘制后更改颜色

Question

I have asked a similar question a while ago here, but didn't get an answer. The original question was about changing the color of a shape after clicking on it. But I am puzzled on how to access the shape at all after it is drawn.

This is my paintComponent method

    @Override
protected void paintComponent(Graphics graph) {
    super.paintComponent(graph);
    Graphics2D g = (Graphics2D) graph;
    // smooth graphics
    g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    // moving to the middle of the panel
    g.translate(this.getWidth()/2, this.getHeight()/2);

    // painting colored arcs
    for(int i = 0; i < 4; i++) {
        g.setColor(dimColors[i]);
        g.fill(arcs[i]);            
    }

    // painting borders
    g.setColor(Color.BLACK);
    g.setStroke(new BasicStroke(5F));
    g.drawLine(-98, 0, 98, 0);
    g.drawLine(0, -98, 0, 98);      
    g.draw(circle);     

    // painting central white circle
    g.setColor(Color.WHITE);
    g.fill(smallCircle);        
    g.setColor(Color.BLACK);
    g.draw(smallCircle);    

}

the arcs[] array contains a bunch of Arc2D's that are drawn on the panel. My question is now, if I want to change the color of, for example arcs[0], how do I do that?

Thanks!

EDIT: I now have this MouseAdapter event

     private class MyMouseAdapter extends MouseAdapter {
     public void mousePressed(MouseEvent e) {

         Point p = e.getPoint();
         Component c = getComponentAt(p);

         Graphics g = c.getGraphics();

         dimColors[1] = Color.RED;

         paintComponent(g);

     }
 }

And it works, it changes the color of arc[1] because arcs[1] has dimColors[1] set as color when drawing it.

However, I still can't figure out how to check wether the right arc was clicked. Right now you just click anywhere on the graphics panel and it changes the color of that specific arc

Answer 1

This doesn't answer your earlier question, however it does answer your question of click detection. To do this it is best to use Graphics2D because it is a lot easier to write than most other options. Here is an example:

     public class GraphicsPanel extends JPanel implements MouseListener
    {   
            private Rectangle2D rect;

First we create our Graphics2D rectangle rect.

        public void paintComponent(Graphics g)
        {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D)(g);
            g2d.setColor(Color.GREEN);
            rect = new Rectangle2D.Double(70, 70, 100, 100);
            g2d.fill(rect);
            this.addMouseListener(this);
        }

And then we override the paintComponent method and create our new Rectangle2D.Double object. We then fill the rectangle with g2d.fill() and then add a mouse listener to the JPanel.

        public void mousePressed(MouseEvent e) 
            {

               if(rect.contains(e.getX(), e.getY()))
                    System.out.println("Rectangle clicked");
            }
    }

Finally, we need to see if that rectangle contains the point where the user clicked. To do this, simply see if the rectangle we created contains the user's click location by using the Rectangle2D.double's contains(int x, int y) method. That's it!

Answer 2

if I want to change the color of, for example arcs[0], how do I do that?

A line (or whatever) only exists as a bunch of pixels that were painted in the original color. To change its color you must change the current color and draw it again.