JPanel-> (znikające) rysowanie myszką

Cześć,
napisałem aplikację, która ma za zadanie rysować obrazek myszką na JPanelu (taki mini paint). LPM->rysowanie, PPM->gumka, Scroll->rozmiar ołówka, Scroll_button->czyści ekran. Moje pytanie brzmi: Jak załadować to wszystko do BufferedImage, żeby przy przesuwaniu okna lub minimalizowaniu go nie znikało mi to co narysowałem?
[code]
{
drawing_area = new JPanel();
drawing_area.setVisible(false);
drawing_area.addMouseWheelListener(new MouseWheelListener() {
public void mouseWheelMoved(MouseWheelEvent evt) {
drawing_areaMouseWheelMoved(evt);
}
});

			drawing_area.addMouseListener(new MouseAdapter() {
				public void mouseEntered(MouseEvent evt) {
					drawing_areaMouseEntered(evt);
				}
				public void mouseExited(MouseEvent evt) {
					drawing_areaMouseExited(evt);
				}
				public void mouseReleased(MouseEvent evt) {
					drawing_areaMouseReleased(evt);
				}
				public void mousePressed(MouseEvent evt) {
					drawing_areaMousePressed(evt);
				}
				public void mouseClicked(MouseEvent evt) {
					drawing_areaMouseClicked(evt);
				}
			});
			drawing_area.addMouseMotionListener(new MouseMotionAdapter() {					
				public void mouseMoved(MouseEvent evt) {
					drawing_areaMouseMoved(evt);
				}
				public void mouseDragged(MouseEvent evt) {
					drawing_areaMouseDragged(evt);
				}
				
			});				
			
			
		}

...

private void drawing_areaMouseDragged(MouseEvent evt) 
{
	
	x=evt.getX()+5;
	y=evt.getY()+50;
	if (a==1)
	{			
		Graphics2D g2 = (Graphics2D)getGraphics();
		
		switch (col) 
		{
		case 1:
			g2.setColor(Color.BLACK);
			break;
		case 2:
			g2.setColor(Color.RED);
			break;
		case 3:
			g2.setColor(Color.YELLOW);
			break;
		case 4:
			g2.setColor(Color.BLUE);
			break;
		case 5:
			g2.setColor(Color.GREEN);
			break;
		default:
			break;
		}
			
		
		g2.fillOval(x, y, point_size, point_size);
		
	
	}
	if (a==0)
	{			
		getGraphics().setColor(new java.awt.Color(0,255,255));			
		getGraphics().clearRect(x,y,point_size*2,point_size*2);
	}
}
private void drawing_areaMouseClicked(MouseEvent evt) 
{
	
}

private void drawing_areaMousePressed(MouseEvent evt) {
	int button = evt.getButton();
	if (button == MouseEvent.BUTTON3) {a=0;}
	if (button == MouseEvent.BUTTON1) {a=1;}
	if (button == MouseEvent.BUTTON2) {a=2; repaint();}
}

private void drawing_areaMouseReleased(MouseEvent evt) {
	
}

private void drawing_areaMouseExited(MouseEvent evt) 
{
a=2;
}

private void drawing_areaMouseEntered(MouseEvent evt)
{
	
}

private void drawing_areaMouseMoved(MouseEvent evt) 
{
	//System.out.println("("+evt.getX()+","+evt.getY()+")");
}

private void drawing_areaMouseWheelMoved(MouseWheelEvent evt) 
{
	int rotate = evt.getWheelRotation();
	if(rotate == -1 && point_size > 2)
		point_size--;
	if(rotate == 1 && point_size < 9)
		point_size++;
}
private void black_bActionPerformed(ActionEvent evt) {
	col = 1;
	
}

private void red_bActionPerformed(ActionEvent evt) {
	
	col = 2;
}

private void yellow_bActionPerformed(ActionEvent evt) {
	
	col = 3;
}

private void blue_bActionPerformed(ActionEvent evt) {
	
	col = 4;
}

private void green_bActionPerformed(ActionEvent evt) {
	
	col = 5;
}

[/code]