Drop Shadow On JInternalFrame

Question

I am trying to adapt Romain Guy's DropShadowPanel to make a drop shadow on a JInternalFrame. It seems as the shadow is drawn outside the clip of the frame I have to somehow increase the clip size to see the shadow. It's nearly working but the shadow isn't working when the frame is moved.
I also tried putting an empty border around the frame and, curiously, that worked in Metal LaF but not Windows which is what I need.
Can anyone help?
Note that this class uses Swing labs shadow renderer and GraphicsUtils.
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.LayoutManager;
import java.awt.image.BufferedImage;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.JInternalFrame;
import org.jdesktop.swingx.graphics.ShadowRenderer;
import org.jdesktop.swingx.graphics.GraphicsUtilities;
public class DropShadowInternalFrame extends JInternalFrame implements PropertyChangeListener {
    // angle and distance of the shadow from the original subjects
    private float angle = 45.0f;
    private int distance = 20;
    // cached values for fast painting
    private int distance_x = 0;
    private int distance_y = 0;
    // when shadow member is equaled to null, the factory is asked to
    // re-generated it
    private BufferedImage shadow = null;
    private ShadowRenderer factory = null;
    public DropShadowInternalFrame(String title, boolean resizable, boolean closable,
            boolean maximizable, boolean iconifiable) {
         super(title, resizable, closable, maximizable, iconifiable);
        setShadowFactory(factory);       
        computeShadowPosition();
        this.setOpaque(true);
    public ShadowRenderer getShadowFactory() {
        return factory;
    public void setShadowFactory(ShadowRenderer factory) {
        if (factory == null) {
            factory = new ShadowRenderer();
        if (factory != this.factory){
            if (this.factory != null) {
                this.factory.removePropertyChangeListener(this);
            this.factory = factory;
            this.factory.addPropertyChangeListener(this);
            shadow = null;
            repaint();
    public float getAngle() {
        return angle;
    public void setAngle(final float angle) {
        this.angle = angle;
        computeShadowPosition();
        repaint();
    public int getDistance() {
        return distance;
    public void setDistance(final int distance) {
        this.distance = distance;
        computeShadowPosition();
        repaint();
    private void computeShadowPosition() {
        double angleRadians = Math.toRadians(angle);
        distance_x = (int) (Math.cos(angleRadians) * distance) - factory.getSize() ;
        distance_y = (int) (Math.sin(angleRadians) * distance) - factory.getSize();
    @Override
    public boolean isOpaque() {
        return false;
    @Override
    public void doLayout() {
        super.doLayout();
        shadow = null;
    @Override
    public void paint(Graphics g) {
         Graphics g3 = g.create();
            BufferedImage buffer =
                    GraphicsUtilities.createCompatibleTranslucentImage(getWidth(),
                                                                       getHeight());
            Graphics2D g2 = buffer.createGraphics();
            super.paint(g2);
            shadow = factory.createShadow(buffer);          
            g2.dispose();
            g.setClip(g3.getClip().getBounds().x,
                      g3.getClip().getBounds().y,
                      g3.getClip().getBounds().width + 20,
                      g3.getClip().getBounds().height + 20);
            g.drawImage(shadow, distance_x, distance_y, shadow.getWidth(), shadow.getHeight(), null);        
            g.drawImage(buffer, 0, 0, null);         
            System.out.println("distance_x = " + distance_x + "; distance_y = " + distance_y);           
     g.setClip(g3. getClip());
    public void propertyChange(PropertyChangeEvent evt) {
        shadow = null;
        computeShadowPosition();
        repaint();
}

Answer 1

Modifying the clip to draw outside of the frame bounds is not a good idea. Swing expects components to paint only within their bounds. So when you move the frame from position A to position B, swing takes care that the old frame bounds are repainted by the underlying component (desktop pane). The stuff you painted outside of the frame bounds will not be cleared. Maybe you will have some success if you ask the desktop pane to repaint after every resize/move of the internal frame.
The approach with the empty border seemed more promising and I gave it a try. First thing I found is that some InternalFrameUI's install their own border on the frame. See the updateUI() method below to see how I tried to work around that problem. This works for Metal, Motif and Windows L&F (only when using the windows classic theme).
Second thing I found is that when using the windows XP theme, the BasicInternalFrameUI.Handler.layoutContainer() method sets the bounds of the internal frame's "north pane" to the whole width of the frame (ignoring any borders). If you really only need this to work in one specific L&F, I imagine it would be possible to subclass the WindowsInternalFrameUI, override the createNorthPane() method to return a subclass of WindowsInternalFrameTitlePane which in turn override the setBounds() method, reducing the width by the amount needed for the shadow.
The code contains the empty border approach (not working for windows L&F with XP theme enabled). I was not able to test any linux or mac L&Fs.
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.UIManager;
import javax.swing.border.CompoundBorder;
import javax.swing.border.EmptyBorder;
import org.jdesktop.swingx.graphics.GraphicsUtilities;
import org.jdesktop.swingx.graphics.ShadowRenderer;
public class DropShadowInternalFrame extends JInternalFrame {
    private static final int SHADOW_WIDTH = 4;
    private ShadowRenderer shadowRenderer = new ShadowRenderer(SHADOW_WIDTH, 0.5f, Color.BLACK);
    private BufferedImage shadow = null;
    public DropShadowInternalFrame() {
        super("Internal Frame", true, true, true, true);
        // BasicInternalFrameUI.Handler.layoutContainer() uses this property:
        // UIManager.put("InternalFrame.layoutTitlePaneAtOrigin", false);
    public static void main(String[] args) throws Exception {
        UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        // UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        // UIManager.setLookAndFeel("com.sun.java.swing.plaf.motif.MotifLookAndFeel");
        DropShadowInternalFrame dropShadowInternalFrame = new DropShadowInternalFrame();
        dropShadowInternalFrame.setOpaque(false);
        dropShadowInternalFrame.setBounds(20, 20, 300, 300);
        dropShadowInternalFrame.setVisible(true);
        JDesktopPane desktopPane = new JDesktopPane();
        desktopPane.add(dropShadowInternalFrame);
        desktopPane.setDragMode(JDesktopPane.OUTLINE_DRAG_MODE);
        JFrame frame = new JFrame("DropShadowInternalFrame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(desktopPane);
        frame.setSize(500, 500);
        frame.setVisible(true);
    @Override
    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        int w = getWidth();
        int h = getHeight();
        if (shadow == null || shadow.getWidth() != w || shadow.getHeight() != h) {
            // recreate shadow if frame size changed
            BufferedImage frameImg = GraphicsUtilities.createCompatibleTranslucentImage(
                    w - 2 * SHADOW_WIDTH, h - 2 * SHADOW_WIDTH);
            super.paint(frameImg.createGraphics());
            shadow = shadowRenderer.createShadow(frameImg);
        g2.drawImage(shadow, 0, 0, null);
        // Motif ALMOST honors the empty internal frame border
        // comment this line out to see interesting artifacts in Motif LaF
        g2.setClip(0, 0, w - 2 * SHADOW_WIDTH, h - 2 * SHADOW_WIDTH);
        super.paint(g2);
        g2.dispose();
    public void updateUI() {
        super.updateUI();
        // wrap the border of the UI delegate inside our empty border
        setBorder(new CompoundBorder(new EmptyBorder(0, 0, 2 * SHADOW_WIDTH, 2 * SHADOW_WIDTH), getBorder()));
}