added matcher_simple_gpu sample

samples/gpu/matcher_simple.cpp

+#include <iostream>
+
+#include <opencv2/core/core.hpp>
+#include <opencv2/features2d/features2d.hpp>
+#include <opencv2/highgui/highgui.hpp>
+#include <opencv2/gpu/gpu.hpp>
+
+using namespace std;
+using namespace cv;
+using namespace cv::gpu;
+
+void help()
+{
+    cout << "\nThis program demonstrates using SURF_GPU features detector, descriptor extractor and BruteForceMatcher_GPU" << endl;
+    cout << "\nUsage:\n\tmatcher_simple_gpu <image1> <image2>" << endl;
+}
+
+int main(int argc, char* argv[])
+{
+    if (argc != 3)
+    {
+        help();
+        return -1;
+    }
+
+    GpuMat img1(imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE));
+    GpuMat img2(imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE));
+    if (img1.empty() || img2.empty())
+    {
+        cout << "Can't read one of the images" << endl;
+        return -1;
+    }
+
+    SURF_GPU surf;
+
+    // detecting keypoints & computing descriptors
+    GpuMat keypoints1GPU, keypoints2GPU;
+    GpuMat descriptors1GPU, descriptors2GPU;
+    surf(img1, GpuMat(), keypoints1GPU, descriptors1GPU);
+    surf(img2, GpuMat(), keypoints2GPU, descriptors2GPU);
+
+    // matching descriptors
+    BruteForceMatcher_GPU< L2<float> > matcher;
+    GpuMat trainIdx, distance;
+    matcher.matchSingle(descriptors1GPU, descriptors2GPU, trainIdx, distance);
+    
+    // downloading results
+    vector<KeyPoint> keypoints1, keypoints2;
+    vector<float> descriptors1, descriptors2;
+    vector<DMatch> matches;
+    SURF_GPU::downloadKeypoints(keypoints1GPU, keypoints1);
+    SURF_GPU::downloadKeypoints(keypoints2GPU, keypoints2);
+    SURF_GPU::downloadDescriptors(descriptors1GPU, descriptors1);
+    SURF_GPU::downloadDescriptors(descriptors2GPU, descriptors2);
+    BruteForceMatcher_GPU< L2<float> >::matchDownload(trainIdx, distance, matches);
+
+    // drawing the results
+    Mat img_matches;
+    drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
+    imshow("matches", img_matches);
+    waitKey(0);
+
+    return 0;
+}