Java AWT custom CompositeContext & anti-aliasing: RasterFormatException when drawing outside of the client area

Question

I am trying to implement SWT GC-like xor-mode drawing for an AWT Graphics2D. Using the built-in XORComposite is not an option as it does not implement xor-mode drawing as in SWT.

The SWT xor-mode drawing combines source and destination colors via binary exclusive-or. The AWT XORComposite (usable via g2d.setXORMode(Color)) uses a constant xor-color which is combined with the source colors via binary exclusive-or, i.e. the destination colors do not influence the resulting colors.

So the only option that I have in mind is writing my own Composite and CompositeContext implementations which combine source and destination appropriately.

After some reading, I came up with this simple implementation: (Yes I am aware of the getPixel(...), setPixel(...) overhead. I want it to work correctly before optimizing.)

private static class XorComposite implements Composite {

    public static XorComposite INSTANCE = new XorComposite();

    private XorContext context = new XorContext();

    @Override
    public CompositeContext createContext(ColorModel srcColorModel,
            ColorModel dstColorModel, RenderingHints hints) {
        return context;
    }

}

private static class XorContext implements CompositeContext {

    public XorContext() {
    }

    @Override
    public void compose(Raster src, Raster dstIn, WritableRaster dstOut) {
        int w = Math.min(src.getWidth(), dstIn.getWidth());
        int h = Math.min(src.getHeight(), dstIn.getHeight());

        int[] srcRgba = new int[4];
        int[] dstRgba = new int[4];

        for (int x = 0; x < w; x++) {
            for (int y = 0; y < h; y++) {
                src.getPixel(x, y, srcRgba);
                dstIn.getPixel(x, y, dstRgba);
                for (int i = 0; i < 3; i++) {
                    dstRgba[i] ^= srcRgba[i];
                }
                dstOut.setPixel(x, y, dstRgba);
            }
        }
    }

    @Override
    public void dispose() {
    }

}

This implementation works fine when anti-aliasing is disabled. If anti-aliasing is enabled it works as long as my drawings are fully visible, i.e. inside my JPanel that I draw onto. But if a drawing is crossing the JPanel's bounds, a RasterFormatException is thrown:

Exception in thread "AWT-EventQueue-0" java.awt.image.RasterFormatException: (y + height) is outside raster
    at sun.awt.image.IntegerInterleavedRaster.createWritableChild(IntegerInterleavedRaster.java:470)
    at sun.awt.image.IntegerInterleavedRaster.createChild(IntegerInterleavedRaster.java:514)
    at sun.java2d.pipe.GeneralCompositePipe.renderPathTile(GeneralCompositePipe.java:106)
    at sun.java2d.pipe.AAShapePipe.renderTiles(AAShapePipe.java:201)
    at sun.java2d.pipe.AAShapePipe.fillParallelogram(AAShapePipe.java:102)
    at sun.java2d.pipe.PixelToParallelogramConverter.fillRectangle(PixelToParallelogramConverter.java:322)
    at sun.java2d.pipe.PixelToParallelogramConverter.fill(PixelToParallelogramConverter.java:159)
    at sun.java2d.pipe.ValidatePipe.fill(ValidatePipe.java:160)
    at sun.java2d.SunGraphics2D.fill(SunGraphics2D.java:2422)
    at org.eclipse.gef4.graphics.examples.AwtXorTestPanel.paint(AwtXorTest.java:117)
    ... (irrelevant)

Notably, my Composite/CompositeContext does not throw the exception, but the AWT internals throw the exception when trying to create the Raster objects that it wants to pass to my CompositeContext.

Unfortunately, the PixelToParallelogramConverter is only used for custom Composites when anti-aliasing is enabled. The built-in XORComposite, for example, uses a native method to draw. I assume an AWT bug, but I am unsure.

Help would be greatly appreciated :)

Update:

As Durandal suggested, I tested the code with java-6-sun and java-1.6.0-openjdk. I found out that the OpenJDK throws the exception and the Sun-JDK does not. Consequently, I reported the bug at the OpenJDK bug tracker.

I will update this question when the problem is resolved. Please visit the corresponding OpenJDK bug for information on the current progress.

regards, Matthias

Here is an example program, so you can test it locally:

/*******************************************************************************
 * Copyright (c) 2013 itemis AG and others.
 * 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     Matthias Wienand (itemis AG) - initial API and implementation
 * 
 *******************************************************************************/
package org.eclipse.gef4.graphics.examples;

import java.awt.Color;

public class AwtXorTest extends JApplet {

    private static final long serialVersionUID = 1L;

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setTitle("AWT XorMode Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JApplet applet = new AwtXorTest();
        applet.init();
        frame.getContentPane().add(applet);
        frame.pack();
        frame.setVisible(true);
    }

    @Override
    public void init() {
        JPanel panel = new AwtXorTestPanel();
        getContentPane().add(panel);
    }

}

class AwtXorTestPanel extends JPanel {

    private static class XorComposite implements Composite {

        public static XorComposite INSTANCE = new XorComposite();

        private XorContext context = new XorContext();

        @Override
        public CompositeContext createContext(ColorModel srcColorModel,
                ColorModel dstColorModel, RenderingHints hints) {
            return context;
        }

    }

    private static class XorContext implements CompositeContext {

        public XorContext() {
        }

        @Override
        public void compose(Raster src, Raster dstIn, WritableRaster dstOut) {
            int w = Math.min(src.getWidth(), dstIn.getWidth());
            int h = Math.min(src.getHeight(), dstIn.getHeight());

            int[] srcRgba = new int[4];
            int[] dstRgba = new int[4];

            for (int x = 0; x < w; x++) {
                for (int y = 0; y < h; y++) {
                    src.getPixel(x, y, srcRgba);
                    dstIn.getPixel(x, y, dstRgba);
                    for (int i = 0; i < 3; i++) {
                        dstRgba[i] ^= srcRgba[i];
                    }
                    dstOut.setPixel(x, y, dstRgba);
                }
            }
        }

        @Override
        public void dispose() {
        }

    }

    private static final long serialVersionUID = 1L;

    public AwtXorTestPanel() {
        setPreferredSize(new Dimension(640, 480));
    }

    @Override
    public void paint(Graphics graphics) {
        Graphics2D g2d = (Graphics2D) graphics;

        // comment out to see it working:
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);

        g2d.setComposite(XorComposite.INSTANCE);
        g2d.setColor(new Color(0, 255, 255)); // resulting color should be red
        g2d.fill(new Rectangle(100, 100, 500, 500));
    }

}

Answer 1

Caveat: It's been a while since I've touched Rasters.

It looks like you are probably accessing pixels outside the raster.

Rasters have a minX, minY, so your loops need to be something like this:

int srcMinX = src.getMinX();
int srcMinY = src.getMinY();
int dstInMinX = dstIn.getMinX();
int dstInMinY = dstIn.getMinY();
int dstOutMinX = dstOut.getMinX();
int dstOutMinY = dstOut.getMinY();

for (int x = 0; x < w; x++) {
    for (int y = 0; y < h; y++) {
        src.getPixel(x+srcMinX, y+srcMinY, srcRgba);
        dstIn.getPixel(x+dstInMinX, y+dstInMinY, dstRgba);
        for (int i = 0; i < 3; i++) {
            dstRgba[i] ^= srcRgba[i];
        }
        dstOut.setPixel(x+dstOutMinX, y+dstOutMinY, dstRgba);
    }
}