Add function to sort keypoints that are calculated in parallel to ensure stable output

modules/features2d/include/opencv2/features2d.hpp

@@ -117,6 +117,10 @@ public:
      * Remove duplicated keypoints.
      */
     static void removeDuplicated( std::vector<KeyPoint>& keypoints );
+    /*
+     * Remove duplicated keypoints and sort the remaining keypoints
+     */
+    static void removeDuplicatedSorted( std::vector<KeyPoint>& keypoints );
 
     /*
      * Retain the specified number of the best keypoints (according to the response)

modules/features2d/src/keypoint.cpp

@@ -221,4 +221,44 @@ void KeyPointsFilter::removeDuplicated( std::vector<KeyPoint>& keypoints )
     keypoints.resize(j);
 }
 
+struct KeyPoint12_LessThan
+{
+    bool operator()(const KeyPoint &kp1, const KeyPoint &kp2) const
+    {
+        if( kp1.pt.x != kp2.pt.x )
+            return kp1.pt.x < kp2.pt.x;
+        if( kp1.pt.y != kp2.pt.y )
+            return kp1.pt.y < kp2.pt.y;
+        if( kp1.size != kp2.size )
+            return kp1.size > kp2.size;
+        if( kp1.angle != kp2.angle )
+            return kp1.angle < kp2.angle;
+        if( kp1.response != kp2.response )
+            return kp1.response > kp2.response;
+        if( kp1.octave != kp2.octave )
+            return kp1.octave > kp2.octave;
+        return kp1.class_id > kp2.class_id;
+    }
+};
+
+void KeyPointsFilter::removeDuplicatedSorted( std::vector<KeyPoint>& keypoints )
+{
+    int i, j, n = (int)keypoints.size();
+
+    if (n < 2) return;
+
+    std::sort(keypoints.begin(), keypoints.end(), KeyPoint12_LessThan());
+
+    for( i = 0, j = 1; j < n; ++j )
+    {
+        const KeyPoint& kp1 = keypoints[i];
+        const KeyPoint& kp2 = keypoints[j];
+        if( kp1.pt.x != kp2.pt.x || kp1.pt.y != kp2.pt.y ||
+            kp1.size != kp2.size || kp1.angle != kp2.angle ) {
+            keypoints[++i] = keypoints[j];
+        }
+    }
+    keypoints.resize(i + 1);
+}
+
 }