8166038: BufferedImage methods getTileGridXOffset() and getTileGridYOffset() return a non 0 value for sub images

Reviewed-by: jdv, serb

src/java.desktop/share/classes/java/awt/image/BufferedImage.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2020, 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
@@ -1367,7 +1367,7 @@ public class BufferedImage extends java.awt.Image
      * @return the x offset of the tile grid.
      */
     public int getTileGridXOffset() {
-        return raster.getSampleModelTranslateX();
+        return raster.getMinX();
     }
 
     /**
@@ -1377,7 +1377,7 @@ public class BufferedImage extends java.awt.Image
      * @return the y offset of the tile grid.
      */
     public int getTileGridYOffset() {
-        return raster.getSampleModelTranslateY();
+        return raster.getMinY();
     }
 
     /**

test/jdk/java/awt/image/BufferedImage/GetTileGridOffset.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2020, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.awt.image.BufferedImage;
+import java.awt.image.RenderedImage;
+
+/**
+ * @test
+ * @author Martin Desruisseaux
+ */
+public final class GetTileGridOffset {
+    public static void main(final String[] args) {
+        final BufferedImage image = new BufferedImage(
+                20, 20, BufferedImage.TYPE_BYTE_GRAY);
+        validate(image);
+
+        final BufferedImage subImage = image.getSubimage(5, 5, 10, 10);
+        verifyConsistency(subImage);
+        validate(subImage);
+    }
+
+    /**
+     * Verifies that the tile grid offsets of given image are consistent with
+     * other properties (minimum pixel coordinates, minimum tile indices and
+     * tile size). This method verifies the general contract, ignoring
+     * simplifications brought by the {@link BufferedImage} specialization.
+     * The purpose of this method is to demonstrate why tile grid offsets
+     * need to be zero in the {@link BufferedImage} case.
+     */
+    private static void verifyConsistency(final RenderedImage image) {
+        /*
+         * This test will convert the coordinates of an arbitrary pixel in
+         * the first tile to the indices of that tile. The expected result
+         * is (minTileX, minTileY). We take the pixel in lower-right corner
+         * of the first tile (the upper-left corner does not demonstrate
+         * bug 8166038).
+         */
+        final int tileWidth  = image.getTileWidth();
+        final int tileHeight = image.getTileHeight();
+        final int x = image.getMinX() + tileWidth  - 1;
+        final int y = image.getMinY() + tileHeight - 1;
+        /*
+         * From javax.media.jai.PlanarImage.XToTileX(int)
+         * (omitting rounding toward negative infinity):
+         *
+         *  tileX = (x - tileGridXOffset) / tileWidth
+         */
+        int tileX = Math.floorDiv(x - image.getTileGridXOffset(), tileWidth);
+        int tileY = Math.floorDiv(y - image.getTileGridYOffset(), tileHeight);
+        int minTileX = image.getMinTileX();                 // Expected value
+        int minTileY = image.getMinTileY();
+        if (tileX != minTileX || tileY != minTileY) {
+            throw new RuntimeException("Tile indices of upper-left tile"
+                    + " shall be (" + minTileX + ", " + minTileY + ")."
+                    + " But using the provided tileGridOffsets we got"
+                    + " (" + tileX + ", " + tileY + ").");
+        }
+    }
+
+    /**
+     * Verifies that tile grid offsets are zero as required by
+     * {@link BufferedImage} specification.
+     */
+    private static void validate(final BufferedImage image) {
+        final int tileGridXOffset = image.getTileGridXOffset();
+        final int tileGridYOffset = image.getTileGridYOffset();
+        if (tileGridXOffset != 0) {
+            throw new RuntimeException("BufferedImage.getTileGridXOffset()"
+                    + " shall be zero. Got " + tileGridXOffset);
+        }
+        if (tileGridYOffset != 0) {
+            throw new RuntimeException("BufferedImage.getTileGridTOffset()"
+                    + " shall be zero. Got " + tileGridYOffset);
+        }
+    }
+}