Así que estoy creando un JPanel de dibujo a mano libre, que reacciona a los movimientos del mouse y dibuja líneas. Lo tengo funcionando principalmente, excepto por un error en el que se dibuja al azar una línea recta entre líneas. Esa línea recta aleatoria no es intencional, se supone que lo que se dibuja en la imagen de la memoria intermedia es estrictamente lo que el usuario dibuja. Estas líneas dibujadas al azar no son hechas por el usuario y son confusas. Abajo está mi código, ¿alguien puede echar un vistazo? La imagen incluida le brinda una representación visual de lo que está haciendo.

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;
    }
}
}