Add ocl's good features to track implementation.

Additional notes with this commit:
1. Add cornerHarris_dxdy and cornerMinEigenVal_dxdy to get
the interim dx and dy output of Sobel operator;
2. Add minMax_buf to allow user to reuse buffers in minMax;
3. Fix an error when either min or max pointer fed into minMax is NULL;
4. Corner sorter temporarily uses C++ STL's quick sort. A parallel
 selection sort in OpneCL is contained in the implementation but disabled
due to poor performance at the moment.
5. Accuracy test for ocl gfft.

modules/ocl/include/opencv2/ocl/ocl.hpp

@@ -122,8 +122,9 @@ namespace cv
         CV_EXPORTS  void setBinpath(const char *path);
 
         //The two functions below enable other opencl program to use ocl module's cl_context and cl_command_queue
+        //returns cl_context * 
         CV_EXPORTS void* getoclContext();
-
+        //returns cl_command_queue *
         CV_EXPORTS void* getoclCommandQueue();
 
         //explicit call clFinish. The global command queue will be used.
@@ -461,6 +462,7 @@ namespace cv
         // support all C1 types
 
         CV_EXPORTS void minMax(const oclMat &src, double *minVal, double *maxVal = 0, const oclMat &mask = oclMat());
+        CV_EXPORTS void minMax_buf(const oclMat &src, double *minVal, double *maxVal, const oclMat &mask, oclMat& buf);
 
         //! finds global minimum and maximum array elements and returns their values with locations
         // support all C1 types
@@ -789,7 +791,11 @@ namespace cv
         CV_EXPORTS void integral(const oclMat &src, oclMat &sum, oclMat &sqsum);
         CV_EXPORTS void integral(const oclMat &src, oclMat &sum);
         CV_EXPORTS void cornerHarris(const oclMat &src, oclMat &dst, int blockSize, int ksize, double k, int bordertype = cv::BORDER_DEFAULT);
+        CV_EXPORTS void cornerHarris_dxdy(const oclMat &src, oclMat &dst, oclMat &Dx, oclMat &Dy,
+            int blockSize, int ksize, double k, int bordertype = cv::BORDER_DEFAULT);
         CV_EXPORTS void cornerMinEigenVal(const oclMat &src, oclMat &dst, int blockSize, int ksize, int bordertype = cv::BORDER_DEFAULT);
+        CV_EXPORTS void cornerMinEigenVal_dxdy(const oclMat &src, oclMat &dst, oclMat &Dx, oclMat &Dy,
+            int blockSize, int ksize, int bordertype = cv::BORDER_DEFAULT);
 
         ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         ///////////////////////////////////////////CascadeClassifier//////////////////////////////////////////////////////////////////
@@ -1253,6 +1259,52 @@ namespace cv
         public:
             explicit BFMatcher_OCL(int norm = NORM_L2) : BruteForceMatcher_OCL_base(norm == NORM_L1 ? L1Dist : norm == NORM_L2 ? L2Dist : HammingDist) {}
         };
+
+        class CV_EXPORTS GoodFeaturesToTrackDetector_OCL
+        {
+        public:
+            explicit GoodFeaturesToTrackDetector_OCL(int maxCorners = 1000, double qualityLevel = 0.01, double minDistance = 0.0,
+                int blockSize = 3, bool useHarrisDetector = false, double harrisK = 0.04);
+
+            //! return 1 rows matrix with CV_32FC2 type
+            void operator ()(const oclMat& image, oclMat& corners, const oclMat& mask = oclMat());
+            //! download points of type Point2f to a vector. the vector's content will be erased
+            void downloadPoints(const oclMat &points, vector<Point2f> &points_v);
+
+            int maxCorners;
+            double qualityLevel;
+            double minDistance;
+
+            int blockSize;
+            bool useHarrisDetector;
+            double harrisK;
+            void releaseMemory()
+            {
+                Dx_.release();
+                Dy_.release();
+                eig_.release();
+                minMaxbuf_.release();
+                tmpCorners_.release();
+            }
+        private:
+            oclMat Dx_;
+            oclMat Dy_;
+            oclMat eig_;
+            oclMat minMaxbuf_;
+            oclMat tmpCorners_;
+        };
+
+        inline GoodFeaturesToTrackDetector_OCL::GoodFeaturesToTrackDetector_OCL(int maxCorners_, double qualityLevel_, double minDistance_,
+            int blockSize_, bool useHarrisDetector_, double harrisK_)
+        {
+            maxCorners = maxCorners_;
+            qualityLevel = qualityLevel_;
+            minDistance = minDistance_;
+            blockSize = blockSize_;
+            useHarrisDetector = useHarrisDetector_;
+            harrisK = harrisK_;
+        }
+
         /////////////////////////////// PyrLKOpticalFlow /////////////////////////////////////
         class CV_EXPORTS PyrLKOpticalFlow
         {

modules/ocl/include/opencv2/ocl/private/util.hpp

@@ -120,6 +120,33 @@ namespace cv
         cl_mem CV_EXPORTS bindTexture(const oclMat &mat);
         void CV_EXPORTS releaseTexture(cl_mem& texture);
 
+        //Represents an image texture object
+        class CV_EXPORTS TextureCL
+        {
+        public:
+            TextureCL(cl_mem tex, int r, int c, int t)
+                : tex_(tex), rows(r), cols(c), type(t) {}
+            ~TextureCL()
+            {
+                openCLFree(tex_);
+            }
+            operator cl_mem() 
+            {
+                return tex_;
+            }
+            cl_mem const tex_;
+            const int rows;
+            const int cols;
+            const int type;
+        private:
+            //disable assignment
+            void operator=(const TextureCL&);
+        };
+        // bind oclMat to OpenCL image textures and retunrs an TextureCL object
+        // note:
+        //   for faster clamping, there is no buffer padding for the constructed texture
+        Ptr<TextureCL> CV_EXPORTS bindTexturePtr(const oclMat &mat);
+
         // returns whether the current context supports image2d_t format or not
         bool CV_EXPORTS support_image2d(Context *clCxt = Context::getContext());
 
@@ -132,7 +159,7 @@ namespace cv
         };
         template<DEVICE_INFO _it, typename _ty>
         _ty queryDeviceInfo(cl_kernel kernel = NULL);
-        //info should have been pre-allocated
+
         template<>
         int CV_EXPORTS queryDeviceInfo<WAVEFRONT_SIZE, int>(cl_kernel kernel);
         template<>