How to use ROC curve class in opencv?

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In evaluate.cpp file

computeRecallPrecisionCurve( const std::vector<std::vector<DMatch> >& matches1to2,
                                             const std::vector<std::vector<uchar> >& correctMatches1to2Mask,
                                            std::vector<Point2f>& recallPrecisionCurve )

class is used to calculate ROC curve for feature matching for benchmark estimation. How did it works, How the correctmatches1tomask is calculated.