Restricting the drawing area on a JPanel and saving graphics states

Question

The purpose of the black JPanel is drawing.

• How can I restrict the drawing to the radius of the circle formed by the lines?

• Is there a way to save the graphics object state so that more drawing can be added to it as well as adding an undo function?

public void paintComponent(Graphics g)
{
    super.paintComponent(g);

    sectors = 12;

    Graphics2D g2d = (Graphics2D) g;    
    g2d.setColor(Color.RED);

    sector = new Line2D.Double(getWidth()/2, 0, getWidth()/2, getHeight());
    //g2d.setClip(new Ellipse2D.Double(getWidth()/2,getHeight()/2, radius, radius));


    //draws the sectors on the screen
    for(int i=0; i<sectors; i++)
    {   
        g2d.draw(sector);
        g2d.rotate(Math.toRadians(30),getWidth()/2,getHeight()/2);
    }

    //draws the doily
    if(dragging)
    {
        for(int i=0; i<sectors; i++)
        {
            g2d.fillOval((int) draw.getX(), (int) draw.getY(),20, 20);
            g2d.rotate(Math.toRadians(30), getWidth()/2, getHeight()/2);
        }

        //saves the current drawing in a stack
        graphics.push(g2d);
    }
}

Answer 1

For your first question,

You would need to read up on Java's Custom Painting http://docs.oracle.com/javase/tutorial/uiswing/painting/

Not to discourage you but this is a tricky process, To answer your question there is a similar post here Java Change shape of JPanel