Simple sample of using the Codename One glass pane

GlasspaneSample.java

Form hi = new Form("Glass Pane", new BoxLayout(BoxLayout.Y_AXIS));
Style s = UIManager.getInstance().getComponentStyle("Label");
s.setFgColor(0xff0000);
s.setBgTransparency(0);
Image warningImage = FontImage.createMaterial(FontImage.MATERIAL_WARNING, s).toImage();
TextField tf1 = new TextField("My Field");
tf1.getAllStyles().setMarginUnit(Style.UNIT_TYPE_DIPS);
tf1.getAllStyles().setMargin(5, 5, 5, 5);
hi.add(tf1);
hi.setGlassPane((g, rect) -> {
    int x = tf1.getAbsoluteX() + tf1.getWidth();
    int y = tf1.getAbsoluteY();
    x -= warningImage.getWidth() / 2;
    y += (tf1.getHeight() / 2 - warningImage.getHeight() / 2);
    g.drawImage(warningImage, x, y);
});
hi.show();

Sample usage of the glasspane functionality of Form.

From the Codename One project