Odd behavior when using custom Composite/CompositeContext and antialiasing

Question

Hi,
I created a custom Composite/CompositeContext class and when I use it with antialiasing it causes a black bar to appear. I seems it has nothing to do with the compose() code but just that fact that I set my own Composite object. The submitted code will show you what I mean. There are 3 check boxes 1) allows to use the custom Composite object, 2) allows to ignore the compose() code in the CompositeContext and 3) toggles the antialiasing flag in the rendering hints. When the antialiasing flag is set and the Composite object is used the bar appears regardless of if the compose() method is executed or not. If the Composite object is not used the bar goes away.
The Composite/CompositeContext class performs clipping and gradient paint using a Ellipse2D.Float instance.
a) When the Composite is not used the code does a rectangular fill.
b) When the Composite is used it should clip the rectangular fill to only the inside of a circle and do a gradient merge of background color and current color.
c) If the compose() method is ignored then only the background is painted.
d) When antialiasing is turned on the black bar appears, i) if you ignore the compose() method it remains, ii) if you do not use the Composite object the bar disappears (???)
NOTE: the compose method's code is only for illustration purposes, I know that AlphaComposite, clipping and/or Gradient paint can be used to do what the example does. What I am trying to find out is why the fact of simply using my Composite object with antialiasing will cause the odd behavior.  Been trying to figure it out but haven't, any help is appreciated.
Thx.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import javax.swing.*;
public class TestCustomComposite2
extends JFrame
implements ActionListener {
    private JCheckBox useCompositeChk, useAntialiasingChk, useCompositeContextChk;
    private Shape clippingShape = new Ellipse2D.Float(100, 100, 100, 100);
    private MergeComposite composite = new MergeComposite();
    public TestCustomComposite2() {
        super("Test Custom Composite");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel cp = (JPanel) getContentPane();
        cp.setLayout(new BorderLayout());
        cp.add(new TestCanvas(), BorderLayout.CENTER);
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT, 0, 0));
        panel.add(useCompositeChk = new JCheckBox("Use Composite", true));
        useCompositeChk.addActionListener(this);
        panel.add(useCompositeContextChk = new JCheckBox("Use Composite Context", true));
        useCompositeContextChk.addActionListener(this);
        panel.add(useAntialiasingChk = new JCheckBox("Use Antialiasing"));
        useAntialiasingChk.addActionListener(this);
        cp.add(panel, BorderLayout.SOUTH);
        pack();
        setVisible(true);
    public void actionPerformed(ActionEvent evt) {
        useCompositeContextChk.setEnabled(useCompositeChk.isSelected());
        invalidate();
        repaint();
    private class TestCanvas
    extends JComponent {
        public TestCanvas() {
            setSize(300, 300);
            setPreferredSize(getSize());
        public void paint(Graphics gfx) {
            Dimension size = getSize();
            Graphics2D gfx2D = (Graphics2D) gfx;
            gfx2D.setColor(Color.GRAY);
            gfx2D.fillRect(0, 0, size.width, size.height);
            RenderingHints rh = null;
            if(useAntialiasingChk.isSelected()) {
                rh = gfx2D.getRenderingHints();
                gfx2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            Rectangle r = clippingShape.getBounds();
            //gfx2D.setColor(Color.GREEN);
            //gfx2D.drawRect(r.x, r.y, r.width, r.height);
            gfx2D.setColor(Color.YELLOW);
            gfx2D.fill(clippingShape);
            Composite oldComposite = null;
            if(useCompositeChk.isSelected()) {
                oldComposite = gfx2D.getComposite();
                gfx2D.setComposite(composite);
            gfx2D.setColor(Color.ORANGE);
            gfx2D.fillRect(r.x, r.y, r.width + 1, r.height + 1);
            if(oldComposite != null)
                gfx2D.setComposite(oldComposite);
            if(rh != null)
                gfx2D.setRenderingHints(rh);
    public class MergeComposite
    implements Composite, CompositeContext {
        public CompositeContext createContext(ColorModel srcColorModel,
                                              ColorModel dstColorModel,
                                              RenderingHints hints) {
            return this;
        public void compose(Raster src,
                            Raster dstIn,
                            WritableRaster dstOut) {
            if(!useCompositeContextChk.isSelected())
                return;
            int[] srcPixel = null;
            int[] dstPixel = null;
            for(int sy = src.getMinY(); sy < src.getMinY() + src.getHeight(); sy++) {
                for(int sx = src.getMinX(); sx < src.getMinX() + src.getWidth(); sx++) {
                    int cx = sx - dstOut.getSampleModelTranslateX();
                    int cy = sy - dstOut.getSampleModelTranslateY();
                    if(!clippingShape.contains(cx, cy)) continue;
                    srcPixel = src.getPixel(sx, sy, srcPixel);
                    int ox = dstOut.getMinX() + sx - src.getMinX();
                    int oy = dstOut.getMinY() + sy - src.getMinY();
                    if(ox < dstOut.getMinX() || ox >= dstOut.getMinX() + dstOut.getWidth()) continue;
                    if(oy < dstOut.getMinY() || oy >= dstOut.getMinY() + dstOut.getHeight()) continue;
                    dstPixel = dstIn.getPixel(ox, oy, dstPixel);
                    float mergeFactor = 1.0f * (cy - 100) / 100;
                    dstPixel[0] = merge(mergeFactor, srcPixel[0], dstPixel[0]);
                    dstPixel[1] = merge(mergeFactor, srcPixel[1], dstPixel[1]);
                    dstPixel[2] = merge(mergeFactor, srcPixel[2], dstPixel[2]);
                    dstOut.setPixel(ox, oy, dstPixel);
        protected int merge(float mergeFactor, int src, int dst) {
            return (int) (mergeFactor * src + (1.0f - mergeFactor) * dst);
        public void dispose() {
    public static void main(String[] args) {
        new TestCustomComposite2();
}

Answer 1

I got a better version to work as expected. Though there will probably be issues with the transformation to display coordinates as mentioned before. At least figured out some of the kinks of using a custom Composite/CompositeContext object.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import javax.swing.*;
public class TestCustomComposite2
extends JFrame
implements ActionListener {
    private JCheckBox useCompositeChk, useAntialiasingChk, useCompositeContextChk;
    private Shape clippingShape = new Ellipse2D.Float(100, 100, 100, 100);
    private MergeComposite composite = new MergeComposite();
    public TestCustomComposite2() {
        super("Test Custom Composite");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel cp = (JPanel) getContentPane();
        cp.setLayout(new BorderLayout());
        cp.add(new TestCanvas(), BorderLayout.CENTER);
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT, 0, 0));
        panel.add(useCompositeChk = new JCheckBox("Use Composite", true));
        useCompositeChk.addActionListener(this);
        panel.add(useCompositeContextChk = new JCheckBox("Use Composite Context", true));
        useCompositeContextChk.addActionListener(this);
        panel.add(useAntialiasingChk = new JCheckBox("Use Antialiasing"));
        useAntialiasingChk.addActionListener(this);
        cp.add(panel, BorderLayout.SOUTH);
        pack();
        setVisible(true);
    public void actionPerformed(ActionEvent evt) {
        useCompositeContextChk.setEnabled(useCompositeChk.isSelected());
        invalidate();
        repaint();
    private class TestCanvas
    extends JComponent {
        public TestCanvas() {
            setSize(300, 300);
            setPreferredSize(getSize());
        public void paint(Graphics gfx) {
            Dimension size = getSize();
            Graphics2D gfx2D = (Graphics2D) gfx;
            gfx2D.setColor(Color.GRAY);
            gfx2D.fillRect(0, 0, size.width, size.height);
            RenderingHints rh = null;
            if(useAntialiasingChk.isSelected()) {
                rh = gfx2D.getRenderingHints();
                gfx2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            Rectangle r = clippingShape.getBounds();
            //gfx2D.setColor(Color.GREEN);
            //gfx2D.drawRect(r.x, r.y, r.width, r.height);
            gfx2D.setColor(Color.YELLOW);
            gfx2D.fill(clippingShape);
            Composite oldComposite = null;
            if(useCompositeChk.isSelected()) {
                oldComposite = gfx2D.getComposite();
                gfx2D.setComposite(composite);
            gfx2D.setColor(Color.ORANGE);
            gfx2D.fillRect(r.x, r.y, r.width + 1, r.height + 1);
            if(oldComposite != null)
                gfx2D.setComposite(oldComposite);
            if(rh != null)
                gfx2D.setRenderingHints(rh);
    public class MergeComposite
    implements Composite, CompositeContext {
        public CompositeContext createContext(ColorModel srcColorModel,
                                              ColorModel dstColorModel,
                                              RenderingHints hints) {
            return this;
        public void compose(Raster src,
                            Raster dstIn,
                            WritableRaster dstOut) {
//            dumpRaster("SRC   ", src);
//            dumpRaster("DSTIN ", dstIn);
//            dumpRaster("DSTOUT", dstOut);
//            System.out.println();
            if(dstIn != dstOut)
                dstOut.setDataElements(0, 0, dstIn);
            if(!useCompositeContextChk.isSelected())
                return;
            int[] srcPixel = null;
            int[] dstPixel = null;
            int w = Math.min(src.getWidth(), dstIn.getWidth());
            int h = Math.min(src.getHeight(), dstIn.getHeight());
            int xMax = src.getMinX() + w;
            int yMax = src.getMinY() + h;
            for(int x = src.getMinX(); x < xMax; x++) {
                for(int y = src.getMinY(); y < yMax; y++) {
                    try {
                        // THIS MIGHT NOT WORK ALL THE TIME
                        int cx = x - dstIn.getSampleModelTranslateX();
                        int cy = y - dstIn.getSampleModelTranslateY();
                        if(!clippingShape.contains(cx, cy)) {
                            dstPixel = dstIn.getPixel(x, y, dstPixel);
                            dstOut.setPixel(x, y, dstPixel);
                        else {
                            srcPixel = src.getPixel(x, y, srcPixel);
                            dstPixel = dstIn.getPixel(x, y, dstPixel);
                            float mergeFactor = 1.0f * (cy - 100) / 100;
                            dstPixel[0] = merge(mergeFactor, srcPixel[0], dstPixel[0]);
                            dstPixel[1] = merge(mergeFactor, srcPixel[1], dstPixel[1]);
                            dstPixel[2] = merge(mergeFactor, srcPixel[2], dstPixel[2]);
                            dstOut.setPixel(x, y, dstPixel);
                    catch(Throwable t) {
                        System.out.println(t.getMessage() + " x=" + x + " y=" + y);
        protected int merge(float mergeFactor, int src, int dst) {
            return (int) (mergeFactor * src + (1.0f - mergeFactor) * dst);
        protected void dumpRaster(String lbl,
                                  Raster raster) {
            System.out.print(lbl + ":");
            System.out.print(" mx=" + format(raster.getMinX()));
            System.out.print(" my=" + format(raster.getMinY()));
            System.out.print(" rw=" + format(raster.getWidth()));
            System.out.print(" rh=" + format(raster.getHeight()));
            System.out.print(" tx=" + format(raster.getSampleModelTranslateX()));
            System.out.print(" ty=" + format(raster.getSampleModelTranslateY()));
            System.out.print(" sm=" + raster.getSampleModel().getClass().getName());
            System.out.println();
        protected String format(int value) {
            String txt = Integer.toString(value);
            while(txt.length() < 4)
                txt = " " + txt;
            return txt;
        public void dispose() {
    public static void main(String[] args) {
        new TestCustomComposite2();
}