swingx-master/swingx-common/src/main/java/org/jdesktop/swingx/util/GraphicsUtilities.java
/*
 * $Id$
 *
 * Dual-licensed under LGPL (Sun and Romain Guy) and BSD (Romain Guy).
 *
 * Copyright 2005 Sun Microsystems, Inc., 4150 Network Circle,
 * Santa Clara, California 95054, U.S.A. All rights reserved.
 *
 * Copyright (c) 2006 Romain Guy <romain.guy@mac.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.jdesktop.swingx.util;

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsEnvironment;
import java.awt.Image;
import java.awt.Insets;
import java.awt.RenderingHints;
import java.awt.Transparency;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.JComponent;

/**
 * <p><code>GraphicsUtilities</code> contains a set of tools to perform
 * common graphics operations easily. These operations are divided into
 * several themes, listed below.</p>
 *
 * <h2>Compatible Images</h2>
 *
 * <p>Compatible images can, and should, be used to increase drawing
 * performance. This class provides a number of methods to load compatible
 * images directly from files or to convert existing images to compatibles
 * images.</p>
 *
 * <h2>Creating Thumbnails</h2>
 *
 * <p>This class provides a number of methods to easily scale down images.
 * Some of these methods offer a trade-off between speed and result quality and
 * should be used all the time. They also offer the advantage of producing
 * compatible images, thus automatically resulting into better runtime
 * performance.</p>
 *
 * <p>All these methods are both faster than
 * {@link java.awt.Image#getScaledInstance(int, int, int)} and produce
 * better-looking results than the various <code>drawImage()</code> methods
 * in {@link java.awt.Graphics}, which can be used for image scaling.</p>
 * 
 * <h2>Image Manipulation</h2>
 *
 * <p>This class provides two methods to get and set pixels in a buffered image.
 * These methods try to avoid unmanaging the image in order to keep good
 * performance.</p>
 *
 * @author Romain Guy <romain.guy@mac.com>
 * @author rbair
 * @author Karl Schaefer
 */
@SuppressWarnings("nls")
public class GraphicsUtilities {
    private GraphicsUtilities() {
    }

    // Returns the graphics configuration for the primary screen
    private static GraphicsConfiguration getGraphicsConfiguration() {
        return GraphicsEnvironment.getLocalGraphicsEnvironment().
                    getDefaultScreenDevice().getDefaultConfiguration();
    }

    private static boolean isHeadless() {
        return GraphicsEnvironment.isHeadless();
    }

    /**
     * Converts the specified image into a compatible buffered image.
     * 
     * @param img
     *            the image to convert
     * @return a compatible buffered image of the input
     */
    public static BufferedImage convertToBufferedImage(Image img) {
        BufferedImage buff = createCompatibleTranslucentImage(
                img.getWidth(null), img.getHeight(null));
        Graphics2D g2 = buff.createGraphics();

        try {
            g2.drawImage(img, 0, 0, null);
        } finally {
            g2.dispose();
        }

        return buff;
    }

    /**
     * <p>Returns a new <code>BufferedImage</code> using the same color model
     * as the image passed as a parameter. The returned image is only compatible
     * with the image passed as a parameter. This does not mean the returned
     * image is compatible with the hardware.</p>
     *
     * @param image the reference image from which the color model of the new
     *   image is obtained
     * @return a new <code>BufferedImage</code>, compatible with the color model
     *   of <code>image</code>
     */
    public static BufferedImage createColorModelCompatibleImage(BufferedImage image) {
        ColorModel cm = image.getColorModel();
        return new BufferedImage(cm,
            cm.createCompatibleWritableRaster(image.getWidth(),
                                              image.getHeight()),
            cm.isAlphaPremultiplied(), null);
    }

    /**
     * <p>Returns a new compatible image with the same width, height and
     * transparency as the image specified as a parameter. That is, the
     * returned BufferedImage will be compatible with the graphics hardware.
     * If this method is called in a headless environment, then
     * the returned BufferedImage will be compatible with the source
     * image.</p>
     *
     * @see java.awt.Transparency
     * @see #createCompatibleImage(int, int)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #loadCompatibleImage(java.net.URL)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param image the reference image from which the dimension and the
     *   transparency of the new image are obtained
     * @return a new compatible <code>BufferedImage</code> with the same
     *   dimension and transparency as <code>image</code>
     */
    public static BufferedImage createCompatibleImage(BufferedImage image) {
        return createCompatibleImage(image, image.getWidth(), image.getHeight());
    }

    /**
     * <p>Returns a new compatible image of the specified width and height, and
     * the same transparency setting as the image specified as a parameter.
     * That is, the returned <code>BufferedImage</code> is compatible with
     * the graphics hardware. If the method is called in a headless
     * environment, then the returned BufferedImage will be compatible with
     * the source image.</p>
     *
     * @see java.awt.Transparency
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #loadCompatibleImage(java.net.URL)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param width the width of the new image
     * @param height the height of the new image
     * @param image the reference image from which the transparency of the new
     *   image is obtained
     * @return a new compatible <code>BufferedImage</code> with the same
     *   transparency as <code>image</code> and the specified dimension
     */
    public static BufferedImage createCompatibleImage(BufferedImage image,
                                                      int width, int height) {
        return isHeadless() ?
                new BufferedImage(width, height, image.getType()) :
                getGraphicsConfiguration().createCompatibleImage(width, height,
                                                   image.getTransparency());
    }

    /**
     * <p>Returns a new opaque compatible image of the specified width and
     * height. That is, the returned <code>BufferedImage</code> is compatible with
     * the graphics hardware. If the method is called in a headless
     * environment, then the returned BufferedImage will be compatible with
     * the source image.</p>
     *
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #loadCompatibleImage(java.net.URL)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param width the width of the new image
     * @param height the height of the new image
     * @return a new opaque compatible <code>BufferedImage</code> of the
     *   specified width and height
     */
    public static BufferedImage createCompatibleImage(int width, int height) {
        return isHeadless() ?
                new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB) :
                getGraphicsConfiguration().createCompatibleImage(width, height);
    }

    /**
     * <p>Returns a new translucent compatible image of the specified width and
     * height. That is, the returned <code>BufferedImage</code> is compatible with
     * the graphics hardware. If the method is called in a headless
     * environment, then the returned BufferedImage will be compatible with
     * the source image.</p>
     *
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleImage(int, int)
     * @see #loadCompatibleImage(java.net.URL)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param width the width of the new image
     * @param height the height of the new image
     * @return a new translucent compatible <code>BufferedImage</code> of the
     *   specified width and height
     */
    public static BufferedImage createCompatibleTranslucentImage(int width,
                                                                 int height) {
        return isHeadless() ?
                new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB) :
                getGraphicsConfiguration().createCompatibleImage(width, height,
                                                   Transparency.TRANSLUCENT);
    }

    /**
     * <p>
     * Returns a new compatible image from a stream. The image is loaded from
     * the specified stream and then turned, if necessary into a compatible
     * image.
     * </p>
     * 
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleImage(int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param in
     *            the stream of the picture to load as a compatible image
     * @return a new translucent compatible <code>BufferedImage</code> of the
     *         specified width and height
     * @throws java.io.IOException
     *             if the image cannot be read or loaded
     */
    public static BufferedImage loadCompatibleImage(InputStream in) throws IOException {
        BufferedImage image = ImageIO.read(in);
        if(image == null) return null;
        return toCompatibleImage(image);
    }

    /**
     * <p>Returns a new compatible image from a URL. The image is loaded from the
     * specified location and then turned, if necessary into a compatible
     * image.</p>
     *
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleImage(int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #toCompatibleImage(java.awt.image.BufferedImage)
     * @param resource the URL of the picture to load as a compatible image
     * @return a new translucent compatible <code>BufferedImage</code> of the
     *   specified width and height
     * @throws java.io.IOException if the image cannot be read or loaded
     */
    public static BufferedImage loadCompatibleImage(URL resource)
            throws IOException {
        BufferedImage image = ImageIO.read(resource);
        return toCompatibleImage(image);
    }

    /**
     * <p>Return a new compatible image that contains a copy of the specified
     * image. This method ensures an image is compatible with the hardware,
     * and therefore optimized for fast blitting operations.</p>
     *
     * <p>If the method is called in a headless environment, then the returned
     * <code>BufferedImage</code> will be the source image.</p>
     *
     * @see #createCompatibleImage(java.awt.image.BufferedImage)
     * @see #createCompatibleImage(java.awt.image.BufferedImage, int, int)
     * @see #createCompatibleImage(int, int)
     * @see #createCompatibleTranslucentImage(int, int)
     * @see #loadCompatibleImage(java.net.URL)
     * @param image the image to copy into a new compatible image
     * @return a new compatible copy, with the
     *   same width and height and transparency and content, of <code>image</code>
     */
    public static BufferedImage toCompatibleImage(BufferedImage image) {
        if (isHeadless()) {
            return image;
        }

        if (image.getColorModel().equals(
                getGraphicsConfiguration().getColorModel())) {
            return image;
        }

        BufferedImage compatibleImage =
                getGraphicsConfiguration().createCompatibleImage(
                    image.getWidth(), image.getHeight(),
                    image.getTransparency());
        Graphics g = compatibleImage.getGraphics();
        
        try {
            g.drawImage(image, 0, 0, null);
        } finally {
            g.dispose();
        }

        return compatibleImage;
    }

    /**
     * <p>Returns a thumbnail of a source image. <code>newSize</code> defines
     * the length of the longest dimension of the thumbnail. The other
     * dimension is then computed according to the dimensions ratio of the
     * original picture.</p>
     * <p>This method favors speed over quality. When the new size is less than
     * half the longest dimension of the source image,
     * {@link #createThumbnail(BufferedImage, int)} or
     * {@link #createThumbnail(BufferedImage, int, int)} should be used instead
     * to ensure the quality of the result without sacrificing too much
     * performance.</p>
     *
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int, int)
     * @param image the source image
     * @param newSize the length of the largest dimension of the thumbnail
     * @return a new compatible <code>BufferedImage</code> containing a
     *   thumbnail of <code>image</code>
     * @throws IllegalArgumentException if <code>newSize</code> is larger than
     *   the largest dimension of <code>image</code> or &lt;= 0
     */
    public static BufferedImage createThumbnailFast(BufferedImage image,
                                                    int newSize) {
        float ratio;
        int width = image.getWidth();
        int height = image.getHeight();

        if (width > height) {
            if (newSize >= width) {
                throw new IllegalArgumentException("newSize must be lower than" +
                                                   " the image width");
            } else if (newSize <= 0) {
                 throw new IllegalArgumentException("newSize must" +
                                                    " be greater than 0");
            }

            ratio = (float) width / (float) height;
            width = newSize;
            height = (int) (newSize / ratio);
        } else {
            if (newSize >= height) {
                throw new IllegalArgumentException("newSize must be lower than" +
                                                   " the image height");
            } else if (newSize <= 0) {
                 throw new IllegalArgumentException("newSize must" +
                                                    " be greater than 0");
            }

            ratio = (float) height / (float) width;
            height = newSize;
            width = (int) (newSize / ratio);
        }

        BufferedImage temp = createCompatibleImage(image, width, height);
        Graphics2D g2 = temp.createGraphics();
        
        try {
            g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2.drawImage(image, 0, 0, temp.getWidth(), temp.getHeight(), null);
        } finally {
            g2.dispose();
        }

        return temp;
    }

    /**
     * <p>Returns a thumbnail of a source image.</p>
     * <p>This method favors speed over quality. When the new size is less than
     * half the longest dimension of the source image,
     * {@link #createThumbnail(BufferedImage, int)} or
     * {@link #createThumbnail(BufferedImage, int, int)} should be used instead
     * to ensure the quality of the result without sacrificing too much
     * performance.</p>
     *
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int, int)
     * @param image the source image
     * @param newWidth the width of the thumbnail
     * @param newHeight the height of the thumbnail
     * @return a new compatible <code>BufferedImage</code> containing a
     *   thumbnail of <code>image</code>
     * @throws IllegalArgumentException if <code>newWidth</code> is larger than
     *   the width of <code>image</code> or if code>newHeight</code> is larger
     *   than the height of <code>image</code> or if one of the dimensions
     *   is &lt;= 0
     */
    public static BufferedImage createThumbnailFast(BufferedImage image,
                                                    int newWidth, int newHeight) {
        if (newWidth >= image.getWidth() ||
            newHeight >= image.getHeight()) {
            throw new IllegalArgumentException("newWidth and newHeight cannot" +
                                               " be greater than the image" +
                                               " dimensions");
        } else if (newWidth <= 0 || newHeight <= 0) {
            throw new IllegalArgumentException("newWidth and newHeight must" +
                                               " be greater than 0");
        }

        BufferedImage temp = createCompatibleImage(image, newWidth, newHeight);
        Graphics2D g2 = temp.createGraphics();
        
        try {
            g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2.drawImage(image, 0, 0, temp.getWidth(), temp.getHeight(), null);
        } finally {
            g2.dispose();
        }

        return temp;
    }

    /**
     * <p>Returns a thumbnail of a source image. <code>newSize</code> defines
     * the length of the longest dimension of the thumbnail. The other
     * dimension is then computed according to the dimensions ratio of the
     * original picture.</p>
     * <p>This method offers a good trade-off between speed and quality.
     * The result looks better than
     * {@link #createThumbnailFast(java.awt.image.BufferedImage, int)} when
     * the new size is less than half the longest dimension of the source
     * image, yet the rendering speed is almost similar.</p>
     *
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int, int)
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int, int)
     * @param image the source image
     * @param newSize the length of the largest dimension of the thumbnail
     * @return a new compatible <code>BufferedImage</code> containing a
     *   thumbnail of <code>image</code>
     * @throws IllegalArgumentException if <code>newSize</code> is larger than
     *   the largest dimension of <code>image</code> or &lt;= 0
     */
    public static BufferedImage createThumbnail(BufferedImage image,
                                                int newSize) {
        int width = image.getWidth();
        int height = image.getHeight();

        boolean isTranslucent = image.getTransparency() != Transparency.OPAQUE;
        boolean isWidthGreater = width > height;

        if (isWidthGreater) {
            if (newSize >= width) {
                throw new IllegalArgumentException("newSize must be lower than" +
                                                   " the image width");
            }
        } else if (newSize >= height) {
            throw new IllegalArgumentException("newSize must be lower than" +
                                               " the image height");
        }

        if (newSize <= 0) {
            throw new IllegalArgumentException("newSize must" +
                                               " be greater than 0");
        }

        float ratioWH = (float) width / (float) height;
        float ratioHW = (float) height / (float) width;

        BufferedImage thumb = image;
        BufferedImage temp = null;

        Graphics2D g2 = null;

        try {
            int previousWidth = width;
            int previousHeight = height;
    
            do {
                if (isWidthGreater) {
                    width /= 2;
                    if (width < newSize) {
                        width = newSize;
                    }
                    height = (int) (width / ratioWH);
                } else {
                    height /= 2;
                    if (height < newSize) {
                        height = newSize;
                    }
                    width = (int) (height / ratioHW);
                }
    
                if (temp == null || isTranslucent) {
                    if (g2 != null) {
                        //do not need to wrap with finally
                        //outer finally block will ensure
                        //that resources are properly reclaimed
                        g2.dispose();
                    }
                    temp = createCompatibleImage(image, width, height);
                    g2 = temp.createGraphics();
                    g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                }
                g2.drawImage(thumb, 0, 0, width, height,
                        0, 0, previousWidth, previousHeight, null);
    
                previousWidth = width;
                previousHeight = height;
    
                thumb = temp;
            } while (newSize != (isWidthGreater ? width : height));
        } finally {
            if (g2 != null) {
                g2.dispose();
            }
        }

        if (width != thumb.getWidth() || height != thumb.getHeight()) {
            temp = createCompatibleImage(image, width, height);
            g2 = temp.createGraphics();
            
            try {
                g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                g2.drawImage(thumb, 0, 0, width, height, 0, 0, width, height, null);
            } finally {
                g2.dispose();
            }
            
            thumb = temp;
        }

        return thumb;
    }

    /**
     * <p>Returns a thumbnail of a source image.</p>
     * <p>This method offers a good trade-off between speed and quality.
     * The result looks better than
     * {@link #createThumbnailFast(java.awt.image.BufferedImage, int)} when
     * the new size is less than half the longest dimension of the source
     * image, yet the rendering speed is almost similar.</p>
     *
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int)
     * @see #createThumbnailFast(java.awt.image.BufferedImage, int, int)
     * @see #createThumbnail(java.awt.image.BufferedImage, int)
     * @param image the source image
     * @param newWidth the width of the thumbnail
     * @param newHeight the height of the thumbnail
     * @return a new compatible <code>BufferedImage</code> containing a
     *   thumbnail of <code>image</code>
     * @throws IllegalArgumentException if <code>newWidth</code> is larger than
     *   the width of <code>image</code> or if code>newHeight</code> is larger
     *   than the height of <code>image or if one the dimensions is not &gt; 0</code>
     */
    public static BufferedImage createThumbnail(BufferedImage image,
                                                int newWidth, int newHeight) {
        int width = image.getWidth();
        int height = image.getHeight();

        boolean isTranslucent = image.getTransparency() != Transparency.OPAQUE;

        if (newWidth >= width || newHeight >= height) {
            throw new IllegalArgumentException("newWidth and newHeight cannot" +
                                               " be greater than the image" +
                                               " dimensions");
        } else if (newWidth <= 0 || newHeight <= 0) {
            throw new IllegalArgumentException("newWidth and newHeight must" +
                                               " be greater than 0");
        }

        BufferedImage thumb = image;
        BufferedImage temp = null;

        Graphics2D g2 = null;

        try {
            int previousWidth = width;
            int previousHeight = height;
    
            do {
                if (width > newWidth) {
                    width /= 2;
                    if (width < newWidth) {
                        width = newWidth;
                    }
                }
    
                if (height > newHeight) {
                    height /= 2;
                    if (height < newHeight) {
                        height = newHeight;
                    }
                }
    
                if (temp == null || isTranslucent) {
                    if (g2 != null) {
                        //do not need to wrap with finally
                        //outer finally block will ensure
                        //that resources are properly reclaimed
                        g2.dispose();
                    }
                    temp = createCompatibleImage(image, width, height);
                    g2 = temp.createGraphics();
                    g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                }
                g2.drawImage(thumb, 0, 0, width, height,
                             0, 0, previousWidth, previousHeight, null);
    
                previousWidth = width;
                previousHeight = height;
    
                thumb = temp;
            } while (width != newWidth || height != newHeight);
        } finally {
            if (g2 != null) {
                g2.dispose();
            }
        }

        if (width != thumb.getWidth() || height != thumb.getHeight()) {
            temp = createCompatibleImage(image, width, height);
            g2 = temp.createGraphics();
            
            try {
                g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                g2.drawImage(thumb, 0, 0, width, height, 0, 0, width, height, null);
            } finally {
                g2.dispose();
            }
            
            thumb = temp;
        }

        return thumb;
    }

    /**
     * <p>Returns an array of pixels, stored as integers, from a
     * <code>BufferedImage</code>. The pixels are grabbed from a rectangular
     * area defined by a location and two dimensions. Calling this method on
     * an image of type different from <code>BufferedImage.TYPE_INT_ARGB</code>
     * and <code>BufferedImage.TYPE_INT_RGB</code> will unmanage the image.</p>
     *
     * @param img the source image
     * @param x the x location at which to start grabbing pixels
     * @param y the y location at which to start grabbing pixels
     * @param w the width of the rectangle of pixels to grab
     * @param h the height of the rectangle of pixels to grab
     * @param pixels a pre-allocated array of pixels of size w*h; can be null
     * @return <code>pixels</code> if non-null, a new array of integers
     *   otherwise
     * @throws IllegalArgumentException is <code>pixels</code> is non-null and
     *   of length &lt; w*h
     */
    public static int[] getPixels(BufferedImage img,
                                  int x, int y, int w, int h, int[] pixels) {
        if (w == 0 || h == 0) {
            return new int[0];
        }

        if (pixels == null) {
            pixels = new int[w * h];
        } else if (pixels.length < w * h) {
            throw new IllegalArgumentException("pixels array must have a length" +
                                               " >= w*h");
        }

        int imageType = img.getType();
        if (imageType == BufferedImage.TYPE_INT_ARGB ||
            imageType == BufferedImage.TYPE_INT_RGB) {
            Raster raster = img.getRaster();
            return (int[]) raster.getDataElements(x, y, w, h, pixels);
        }

        // Unmanages the image
        return img.getRGB(x, y, w, h, pixels, 0, w);
    }

    /**
     * <p>Writes a rectangular area of pixels in the destination
     * <code>BufferedImage</code>. Calling this method on
     * an image of type different from <code>BufferedImage.TYPE_INT_ARGB</code>
     * and <code>BufferedImage.TYPE_INT_RGB</code> will unmanage the image.</p>
     *
     * @param img the destination image
     * @param x the x location at which to start storing pixels
     * @param y the y location at which to start storing pixels
     * @param w the width of the rectangle of pixels to store
     * @param h the height of the rectangle of pixels to store
     * @param pixels an array of pixels, stored as integers
     * @throws IllegalArgumentException is <code>pixels</code> is non-null and
     *   of length &lt; w*h
     */
    public static void setPixels(BufferedImage img,
                                 int x, int y, int w, int h, int[] pixels) {
        if (pixels == null || w == 0 || h == 0) {
            return;
        } else if (pixels.length < w * h) {
            throw new IllegalArgumentException("pixels array must have a length" +
                                               " >= w*h");
        }

        int imageType = img.getType();
        if (imageType == BufferedImage.TYPE_INT_ARGB ||
            imageType == BufferedImage.TYPE_INT_RGB) {
            WritableRaster raster = img.getRaster();
            raster.setDataElements(x, y, w, h, pixels);
        } else {
            // Unmanages the image
            img.setRGB(x, y, w, h, pixels, 0, w);
        }
    }

    /**
     * Clears the data from the image.
     * 
     * @param img
     *            the image to erase
     */
    public static void clear(Image img) {
        Graphics g = img.getGraphics();
        
        try {
            if (g instanceof Graphics2D) {
                ((Graphics2D) g).setComposite(AlphaComposite.Clear);
            } else {
                g.setColor(new Color(0, 0, 0, 0));
            }
            
            g.fillRect(0, 0, img.getWidth(null), img.getHeight(null));
        } finally {
            g.dispose();
        }
    }

    /**
     * Draws an image on top of a component by doing a 3x3 grid stretch of the image
     * using the specified insets.
     */
    public static void tileStretchPaint(Graphics g, 
                JComponent comp,
                BufferedImage img,
                Insets ins) {
        
        int left = ins.left;
        int right = ins.right;
        int top = ins.top;
        int bottom = ins.bottom;
        
        // top
        g.drawImage(img,
                    0,0,left,top,
                    0,0,left,top,
                    null);
        g.drawImage(img,
                    left,                 0, 
                    comp.getWidth() - right, top, 
                    left,                 0, 
                    img.getWidth()  - right, top, 
                    null);
        g.drawImage(img,
                    comp.getWidth() - right, 0, 
                    comp.getWidth(),         top, 
                    img.getWidth()  - right, 0, 
                    img.getWidth(),          top, 
                    null);
    
        // middle
        g.drawImage(img,
                    0,    top, 
                    left, comp.getHeight()-bottom,
                    0,    top,   
                    left, img.getHeight()-bottom,
                    null);
        
        g.drawImage(img,
                    left,                  top, 
                    comp.getWidth()-right,      comp.getHeight()-bottom,
                    left,                  top,   
                    img.getWidth()-right,  img.getHeight()-bottom,
                    null);
         
        g.drawImage(img,
                    comp.getWidth()-right,     top, 
                    comp.getWidth(),           comp.getHeight()-bottom,
                    img.getWidth()-right, top,   
                    img.getWidth(),       img.getHeight()-bottom,
                    null);
        
        // bottom
        g.drawImage(img,
                    0,comp.getHeight()-bottom, 
                    left, comp.getHeight(),
                    0,img.getHeight()-bottom,   
                    left,img.getHeight(),
                    null);
        g.drawImage(img,
                    left,                    comp.getHeight()-bottom, 
                    comp.getWidth()-right,        comp.getHeight(),
                    left,                    img.getHeight()-bottom,   
                    img.getWidth()-right,    img.getHeight(),
                    null);
        g.drawImage(img,
                    comp.getWidth()-right,     comp.getHeight()-bottom, 
                    comp.getWidth(),           comp.getHeight(),
                    img.getWidth()-right, img.getHeight()-bottom,   
                    img.getWidth(),       img.getHeight(),
                    null);
    }
}
