Incorrect behavior of JPanel#paintChildren(Graphics) when a JMenu is present?

Question

What I want to do:
Create a JPanel\'s subclass to draw a simple overlay on top of contained components.

Why don\'t I use JLayeredPane

Answer 1

The first string is drawn outside of JPanel (under the JMenu), even though both coordinates are non-negative. The second string is NOT drawn at the bottom right corner. It is pushed up by the height of the JMenu.

In both cases, note that drawString() expects the coordinates to represent the baseline of the String. The font;s ascent and descent are useful in this context. It may be a coincidence that mb.getHeight() and fm.getHeight() are of comparable magnitude.

@Override
protected void paintChildren(Graphics g) {
    super.paintChildren(g);

    // draw some text
    FontMetrics fm = g.getFontMetrics();
    // will be drawn outside panel; under menu
    g.drawString("TEST TOP/LEFT", 0, fm.getAscent());
    final String s = "TEST BOTTOM/RIGHT";
    // will be drawn noticeably above the bottom
    g.drawString(s, getWidth() - fm.stringWidth(s),
        getHeight() - fm.getDescent());
}