add imgproc snippets

samples/cpp/tutorial_code/snippets/imgproc_HoughLinesP.cpp

@@ -0,0 +1,31 @@
+#include <opencv2/imgproc.hpp>
+#include <opencv2/highgui.hpp>
+
+using namespace cv;
+using namespace std;
+
+int main(int argc, char** argv)
+{
+    Mat src, dst, color_dst;
+    if( argc != 2 || !(src=imread(argv[1], 0)).data)
+        return -1;
+
+    Canny( src, dst, 50, 200, 3 );
+    cvtColor( dst, color_dst, COLOR_GRAY2BGR );
+
+    vector<Vec4i> lines;
+    HoughLinesP( dst, lines, 1, CV_PI/180, 80, 30, 10 );
+    for( size_t i = 0; i < lines.size(); i++ )
+    {
+        line( color_dst, Point(lines[i][0], lines[i][1]),
+        Point( lines[i][2], lines[i][3]), Scalar(0,0,255), 3, 8 );
+    }
+    namedWindow( "Source", 1 );
+    imshow( "Source", src );
+
+    namedWindow( "Detected Lines", 1 );
+    imshow( "Detected Lines", color_dst );
+
+    waitKey(0);
+    return 0;
+}