Add QRCode lenient diagonal check (#906)

* Add QRCode lenient diagonal check

Adding diagonal check to solve #897 to prevent false positives for centers

* update tests to expect the increased number of successes

core/src/main/java/com/google/zxing/qrcode/detector/FinderPatternFinder.java

@@ -218,6 +218,34 @@ public class FinderPatternFinder {
         Math.abs(moduleSize - stateCount[4]) < maxVariance;
   }
 
+  /**
+   * @param stateCount count of black/white/black/white/black pixels just read
+   * @return true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios
+   *         used by finder patterns to be considered a match
+   */
+  protected static boolean foundPatternDiagonal(int[] stateCount) {
+    int totalModuleSize = 0;
+    for (int i = 0; i < 5; i++) {
+      int count = stateCount[i];
+      if (count == 0) {
+        return false;
+      }
+      totalModuleSize += count;
+    }
+    if (totalModuleSize < 7) {
+      return false;
+    }
+    float moduleSize = totalModuleSize / 7.0f;
+    float maxVariance = moduleSize / 1.333f;
+    // Allow less than 75% variance from 1-1-3-1-1 proportions
+    return
+            Math.abs(moduleSize - stateCount[0]) < maxVariance &&
+                    Math.abs(moduleSize - stateCount[1]) < maxVariance &&
+                    Math.abs(3.0f * moduleSize - stateCount[2]) < 3 * maxVariance &&
+                    Math.abs(moduleSize - stateCount[3]) < maxVariance &&
+                    Math.abs(moduleSize - stateCount[4]) < maxVariance;
+  }
+
   private int[] getCrossCheckStateCount() {
     crossCheckStateCount[0] = 0;
     crossCheckStateCount[1] = 0;
@@ -227,6 +255,78 @@ public class FinderPatternFinder {
     return crossCheckStateCount;
   }
 
+  /**
+   * After a vertical and horizontal scan finds a potential finder pattern, this method
+   * "cross-cross-cross-checks" by scanning down diagonally through the center of the possible
+   * finder pattern to see if the same proportion is detected.
+   * 
+   * @param centerI row where a finder pattern was detected
+   * @param centerJ center of the section that appears to cross a finder pattern
+   * @param maxCount maximum reasonable number of modules that should be
+   *  observed in any reading state, based on the results of the horizontal scan
+   * @param originalStateCountTotal The original state count total.
+   * @return true if proportions are withing expected limits
+   */
+  private boolean crossCheckDiagonal(int centerI, int centerJ) {
+    int[] stateCount = getCrossCheckStateCount();
+
+    // Start counting up, left from center finding black center mass
+    int i = 0;
+    while (centerI >= i && centerJ >= i && image.get(centerJ - i, centerI - i)) {
+      stateCount[2]++;
+      i++;
+    }
+    if (stateCount[2] == 0) {
+      return false;
+    }
+
+    // Continue up, left finding white space
+    while (centerI >= i && centerJ >= i && !image.get(centerJ - i, centerI - i)) {
+      stateCount[1]++;
+      i++;
+    }
+    if (stateCount[1] == 0) {
+      return false;
+    }
+
+    // Continue up, left finding black border
+    while (centerI >= i && centerJ >= i && image.get(centerJ - i, centerI - i)) {
+      stateCount[0]++;
+      i++;
+    }
+    if (stateCount[0] == 0) {
+      return false;
+    }
+
+    int maxI = image.getHeight();
+    int maxJ = image.getWidth();
+
+    // Now also count down, right from center
+    i = 1;
+    while (centerI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, centerI + i)) {
+      stateCount[2]++;
+      i++;
+    }
+
+    while (centerI + i < maxI && centerJ + i < maxJ && !image.get(centerJ + i, centerI + i)) {
+      stateCount[3]++;
+      i++;
+    }
+    if (stateCount[3] == 0) {
+      return false;
+    }
+
+    while (centerI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, centerI + i)) {
+      stateCount[4]++;
+      i++;
+    }
+    if (stateCount[4] == 0) {
+      return false;
+    }
+
+    return foundPatternDiagonal(stateCount);
+  }
+
   /**
    * <p>After a horizontal scan finds a potential finder pattern, this method
    * "cross-checks" by scanning down vertically through the center of the possible
@@ -408,7 +508,7 @@ public class FinderPatternFinder {
     if (!Float.isNaN(centerI)) {
       // Re-cross check
       centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
-      if (!Float.isNaN(centerJ)) {
+      if (!Float.isNaN(centerJ) && crossCheckDiagonal((int) centerI, (int) centerJ)) {
         float estimatedModuleSize = stateCountTotal / 7.0f;
         boolean found = false;
         for (int index = 0; index < possibleCenters.size(); index++) {

core/src/test/java/com/google/zxing/qrcode/QRCodeBlackBox2TestCase.java

@@ -30,7 +30,7 @@ public final class QRCodeBlackBox2TestCase extends AbstractBlackBoxTestCase {
     addTest(31, 31, 0.0f);
     addTest(29, 29, 90.0f);
     addTest(30, 30, 180.0f);
-    addTest(29, 29, 270.0f);
+    addTest(30, 30, 270.0f);
   }
 
 }

core/src/test/java/com/google/zxing/qrcode/QRCodeBlackBox3TestCase.java

@@ -28,7 +28,7 @@ public final class QRCodeBlackBox3TestCase extends AbstractBlackBoxTestCase {
   public QRCodeBlackBox3TestCase() {
     super("src/test/resources/blackbox/qrcode-3", new MultiFormatReader(), BarcodeFormat.QR_CODE);
     addTest(38, 38, 0.0f);
-    addTest(38, 38, 90.0f);
+    addTest(39, 39, 90.0f);
     addTest(36, 36, 180.0f);
     addTest(39, 39, 270.0f);
   }

core/src/test/java/com/google/zxing/qrcode/QRCodeBlackBox5TestCase.java

@@ -34,7 +34,7 @@ public final class QRCodeBlackBox5TestCase extends AbstractBlackBoxTestCase {
     addTest(19, 19, 0.0f);
     addTest(19, 19, 90.0f);
     addTest(19, 19, 180.0f);
-    addTest(18, 18, 270.0f);
+    addTest(19, 19, 270.0f);
   }
 
 }