converted some OpenCV C samples to C++

samples/cpp/fback.cpp

@@ -0,0 +1,47 @@
+#include <opencv2/video/tracking.hpp>
+#include <opencv2/imgproc/imgproc.hpp>
+#include <opencv2/highgui/highgui.hpp>
+
+using namespace cv;
+
+void drawOptFlowMap(const Mat& flow, Mat& cflowmap, int step,
+                    double, const Scalar& color)
+{
+    for(int y = 0; y < cflowmap.rows; y += step)
+        for(int x = 0; x < cflowmap.cols; x += step)
+        {
+            const Point2f& fxy = flow.at<Point2f>(y, x);
+            line(cflowmap, Point(x,y), Point(cvRound(x+fxy.x), cvRound(y+fxy.y)),
+                 color);
+            circle(cflowmap, Point(x,y), 2, color, -1);
+        }
+}
+
+int main(int, char**)
+{
+    VideoCapture cap(0);
+    
+    if( !cap.isOpened() )
+        return -1;
+    
+    Mat prevgray, gray, flow, cflow, frame;
+    namedWindow("flow", 1);
+    
+    for(;;)
+    {
+        cap >> frame;
+        cvtColor(frame, gray, CV_BGR2GRAY);
+        
+        if( prevgray.data )
+        {
+            calcOpticalFlowFarneback(prevgray, gray, flow, 0.5, 3, 15, 3, 5, 1.2, 0);
+            cvtColor(prevgray, cflow, CV_GRAY2BGR);
+            drawOptFlowMap(flow, cflow, 16, 1.5, CV_RGB(0, 255, 0));
+            imshow("flow", cflow);
+        }
+        if(waitKey(30)>=0)
+            break;
+        std::swap(prevgray, gray);
+    }
+    return 0;
+}