inverted barcode support (#1371)

* also decodes inverted barcode on hint

Co-authored-by: Daniel Dehnhard <daniel@dehnhard.it>

core/src/main/java/com/google/zxing/DecodeHintType.java

@@ -98,6 +98,12 @@ public enum DecodeHintType {
    */
   ALLOWED_EAN_EXTENSIONS(int[].class),
 
+  /**
+   * If true, also tries to decode as inverted image. All configured decoders are simply called a
+   * second time with an inverted image. Doesn't matter what it maps to; use {@link Boolean#TRUE}.
+   */
+  ALSO_INVERTED(Void.class),
+
   // End of enumeration values.
   ;
 

core/src/main/java/com/google/zxing/MultiFormatReader.java

@@ -175,6 +175,17 @@ public final class MultiFormatReader implements Reader {
           // continue
         }
       }
+      if (hints != null && hints.containsKey(DecodeHintType.ALSO_INVERTED)) {
+        // Calling all readers again with inverted image
+        image.getBlackMatrix().flip();
+        for (Reader reader : readers) {
+          try {
+            return reader.decode(image, hints);
+          } catch (ReaderException re) {
+            // continue
+          }
+        }
+      }
     }
     throw NotFoundException.getNotFoundInstance();
   }

core/src/main/java/com/google/zxing/common/BitMatrix.java

@@ -189,6 +189,16 @@ public final class BitMatrix implements Cloneable {
     bits[offset] ^= 1 << (x & 0x1f);
   }
 
+  /**
+   * <p>Flips every bit in the matrix.</p>
+   */
+  public void flip() {
+    int max = bits.length;
+    for (int i = 0; i < max; i++) {
+      bits[i] = ~bits[i];
+    }
+  }
+
   /**
    * Exclusive-or (XOR): Flip the bit in this {@code BitMatrix} if the corresponding
    * mask bit is set.

core/src/test/java/com/google/zxing/common/AbstractBlackBoxTestCase.java

@@ -62,6 +62,7 @@ public abstract class AbstractBlackBoxTestCase extends Assert {
   private final Reader barcodeReader;
   private final BarcodeFormat expectedFormat;
   private final List<TestResult> testResults;
+  private final EnumMap<DecodeHintType,Object> hints = new EnumMap<>(DecodeHintType.class);
 
   public static Path buildTestBase(String testBasePathSuffix) {
     // A little workaround to prevent aggravation in my IDE
@@ -92,6 +93,10 @@ public abstract class AbstractBlackBoxTestCase extends Assert {
     addTest(mustPassCount, tryHarderCount, 0, 0, rotation);
   }
 
+  protected void addHint(DecodeHintType hint) {
+    hints.put(hint, Boolean.TRUE);
+  }
+
   /**
    * Adds a new test for the current directory of images.
    *
@@ -252,7 +257,7 @@ public abstract class AbstractBlackBoxTestCase extends Assert {
 
     String suffix = String.format(" (%srotation: %d)", tryHarder ? "try harder, " : "", (int) rotation);
 
-    Map<DecodeHintType,Object> hints = new EnumMap<>(DecodeHintType.class);
+    Map<DecodeHintType,Object> hints = this.hints.clone();
     if (tryHarder) {
       hints.put(DecodeHintType.TRY_HARDER, Boolean.TRUE);
     }

core/src/test/java/com/google/zxing/inverted/InvertedDataMatrixBlackBoxTestCase.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2008 ZXing authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.zxing.inverted;
+
+import com.google.zxing.BarcodeFormat;
+import com.google.zxing.DecodeHintType;
+import com.google.zxing.MultiFormatReader;
+import com.google.zxing.common.AbstractBlackBoxTestCase;
+
+/**
+ * Inverted barcodes
+ */
+public final class InvertedDataMatrixBlackBoxTestCase extends AbstractBlackBoxTestCase {
+
+  public InvertedDataMatrixBlackBoxTestCase() {
+    super("src/test/resources/blackbox/inverted", new MultiFormatReader(), BarcodeFormat.DATA_MATRIX);
+    addHint(DecodeHintType.ALSO_INVERTED);
+    addTest(1, 1, 0.0f);
+    addTest(1, 1, 90.0f);
+    addTest(1, 1, 180.0f);
+    addTest(1, 1, 270.0f);
+  }
+
+}

core/src/test/java/com/google/zxing/inverted/NoHintInvertedDataMatrixBlackBoxTestCase.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2008 ZXing authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.zxing.inverted;
+
+import com.google.zxing.common.AbstractNegativeBlackBoxTestCase;
+
+/**
+ * Without hint inverted barcodes should not be found.
+ */
+public final class NoHintInvertedDataMatrixBlackBoxTestCase extends AbstractNegativeBlackBoxTestCase {
+
+  public NoHintInvertedDataMatrixBlackBoxTestCase() {
+    super("src/test/resources/blackbox/inverted");
+    addTest(0, 0.0f);
+    addTest(0, 90.0f);
+    addTest(0, 180.0f);
+    addTest(0, 270.0f);
+  }
+
+}

core/src/test/resources/blackbox/inverted/datamatrix-0123456789.txt

@@ -0,0 +1 @@
+0123456789