test/jdk/javax/imageio/plugins/png/ImageCompare.java

/*
 * Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.Raster;

// Utility to compare two BufferedImages for RGB equality
public class ImageCompare {

    public static void compare(BufferedImage oldimg,
                               BufferedImage newimg) {
        int width = oldimg.getWidth();
        int height = oldimg.getHeight();
        if (newimg.getWidth() != width || newimg.getHeight() != height) {
            throw new RuntimeException("Dimensions changed!");
        }

        Raster oldras = oldimg.getRaster();
        ColorModel oldcm = oldimg.getColorModel();
        Raster newras = newimg.getRaster();
        ColorModel newcm = newimg.getColorModel();

        for (int j = 0; j < height; j++) {
            for (int i = 0; i < width; i++) {
                Object oldpixel = oldras.getDataElements(i, j, null);
                int oldrgb = oldcm.getRGB(oldpixel);
                int oldalpha = oldcm.getAlpha(oldpixel);

                Object newpixel = newras.getDataElements(i, j, null);
                int newrgb = newcm.getRGB(newpixel);
                int newalpha = newcm.getAlpha(newpixel);

                if (newrgb != oldrgb ||
                    newalpha != oldalpha) {
                    throw new RuntimeException("Pixels differ at " + i +
                                               ", " + j);
                }
            }
        }
    }
}