Então estou criando um desenho JPanel, que reage aos movimentos do mouse e desenha linhas. Eu consegui trabalhar principalmente, exceto por um bug onde ele desenha aleatoriamente uma linha reta entre as linhas. Essa linha reta aleatória não é intencional, o que é desenhado na imagem em buffer deve ser estritamente o que o usuário desenha. Essas linhas desenhadas aleatoriamente não são feitas pelo usuário e são confusas. Abaixo está o meu código, alguém pode dar uma olhada? A imagem incluída fornece uma representação visual do que está fazendo.

public class NoteDocument extends JPanel implements MouseListener, MouseMotionListener {

private Frame commands;
private JDesktopPane desktop;
private JInternalFrame colorFrame;
private JPanel colorPanel;
private JColorChooser colorChooser;

private enum State { IDLING, DRAGGING };
private enum ButtonPosition { PRESSED, RELEASED };
private enum Shape { SQUARE, RECTANGLE, CIRCLE, OVAL, LINE };

private State state = State.IDLING;
private ButtonPosition position = ButtonPosition.RELEASED;
private Shape shape = null;

//private ArrayList<Point> points = new ArrayList<Point>();
private ArrayList<Point> pressedPoints = new ArrayList<Point>();
private ArrayList<Point> draggedPoints = new ArrayList<Point>();
private ArrayList<Point> releasedPoints = new ArrayList<Point>();

private BufferedImage bufferedImage = null;

public NoteDocument(Frame commands) {
    this.commands = commands;

    setBackground(Color.WHITE);
    addMouseListener(this);
    addMouseMotionListener(this);

    createColorChooser();
}

private void createColorChooser() {
    for (int i = 0; i < commands.getLayeredPane().getComponentCount(); i++) {
        if (commands.getLayeredPane().getComponent(i) instanceof JDesktopPane) {
            desktop = (JDesktopPane) commands.getLayeredPane().getComponent(i);
        }
    }

    colorChooser = new JColorChooser();
    colorPanel = new JPanel();
    colorFrame = new JInternalFrame();

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(colorPanel);
    colorPanel.setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(colorChooser, javax.swing.GroupLayout.PREFERRED_SIZE, 434, javax.swing.GroupLayout.PREFERRED_SIZE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(colorChooser, javax.swing.GroupLayout.PREFERRED_SIZE, 328, javax.swing.GroupLayout.PREFERRED_SIZE)
    );

    colorFrame.add(colorPanel);
    desktop.add(colorFrame);

    colorFrame.pack();
    colorFrame.setVisible(true);
}

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

     Graphics2D g2 = (Graphics2D) g;
     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
                          RenderingHints.VALUE_ANTIALIAS_ON);

      if(bufferedImage == null)
      {
          int panelHeight = this.getHeight();
          int panelWidth = this.getWidth();
          bufferedImage = (BufferedImage) this.createImage(panelHeight, panelWidth);
          Graphics2D gc = bufferedImage.createGraphics(); 
          gc.setColor(Color.WHITE);   
          gc.fillRect(0, 0, panelWidth, panelHeight);
          g2.drawImage(bufferedImage, null, 0, 0);
      }

      //draw pressed points
      for (int a = 0; a < pressedPoints.size(); a++) {        
          Point p1 = pressedPoints.get(a);
          g.drawLine(p1.x, p1.y, p1.x, p1.y);
      }

      //draw draggedPoints        
      for (int b = 0; b < draggedPoints.size() - 2; b++) {
          Point p1 = draggedPoints.get(b);
          Point p2 = draggedPoints.get(b + 1);

          g.drawLine(p1.x, p1.y, p2.x, p2.y);
      }

      //draw released points
      for (int c = 0; c < releasedPoints.size(); c++) {       
          Point p1 = releasedPoints.get(c);

          g.drawLine(p1.x, p1.y, p1.x, p1.y);
      }
}

@Override
public void mouseClicked(MouseEvent e) {}
@Override
public void mouseEntered(MouseEvent e) {}
@Override
public void mouseExited(MouseEvent e) {}

@Override
public void mousePressed(MouseEvent e) {
    if (e.getButton() == MouseEvent.BUTTON1) {
        position = ButtonPosition.PRESSED;
        state = State.DRAGGING;
        pressedPoints.add(e.getPoint());
        this.repaint();     
    } else if (e.getButton() == MouseEvent.BUTTON2) {
        //TODO right click popup
    }
}

@Override
public void mouseReleased(MouseEvent e) {   
    if (state == State.DRAGGING) {
        releasedPoints.add(e.getPoint());
        position = ButtonPosition.RELEASED;
        state = State.IDLING;
        this.repaint();
    }
}

@Override
public void mouseDragged(MouseEvent e) {
    if ((state == State.DRAGGING) && (position == ButtonPosition.PRESSED)) {
        draggedPoints.add(e.getPoint());
        this.repaint();
    } else if ((state == State.IDLING) && (position == ButtonPosition.RELEASED)) {
        return;
    }
}

@Override
public void mouseMoved(MouseEvent e) {
    if ((state == State.DRAGGING) && (position == ButtonPosition.PRESSED)) {
        draggedPoints.add(e.getPoint());
        this.repaint();
    } else if ((state == State.IDLING) && (position == ButtonPosition.RELEASED)) {
        return;
    }
}
}