display fps in webcam demo

src/caffe/util/bbox_util.cpp

@@ -1,4 +1,5 @@
 #include <algorithm>
+#include <ctime>
 #include <map>
 #include <string>
 #include <utility>
@@ -1122,6 +1123,8 @@ vector<cv::Scalar> GetColors(const int n) {
   return colors;
 }
 
+static clock_t start_clock = clock();
+
 template <typename Dtype>
 void VisualizeBBox(const vector<cv::Mat>& images, const Blob<Dtype>* detections,
                    const float threshold, const vector<cv::Scalar>& colors,
@@ -1133,6 +1136,10 @@ void VisualizeBBox(const vector<cv::Mat>& images, const Blob<Dtype>* detections,
   if (num_det == 0 || num_img == 0) {
     return;
   }
+  // Comute FPS.
+  float fps = num_img / (double(clock() - start_clock) / CLOCKS_PER_SEC);
+  start_clock = clock();
+
   const Dtype* detections_data = detections->cpu_data();
   const int width = images[0].cols;
   const int height = images[0].rows;
@@ -1154,8 +1161,23 @@ void VisualizeBBox(const vector<cv::Mat>& images, const Blob<Dtype>* detections,
     all_detections[img_idx][label].push_back(bbox);
   }
 
+  int fontface = cv::FONT_HERSHEY_SIMPLEX;
+  double scale = 1;
+  int thickness = 2;
+  int baseline = 0;
+  char buffer[50];
   for (int i = 0; i < num_img; ++i) {
     cv::Mat image = images[i];
+    // Show FPS.
+    snprintf(buffer, sizeof(buffer), "FPS: %.2f", fps);
+    cv::Size text = cv::getTextSize(buffer, fontface, scale, thickness,
+                                    &baseline);
+    cv::rectangle(image, cv::Point(0, 0),
+                  cv::Point(text.width, text.height + baseline),
+                  CV_RGB(255, 255, 255), CV_FILLED);
+    cv::putText(image, buffer, cv::Point(0, text.height + baseline / 2.),
+                fontface, scale, CV_RGB(0, 0, 0), thickness, 8);
+    // Draw bboxes.
     for (map<int, vector<NormalizedBBox> >::iterator it =
          all_detections[i].begin(); it != all_detections[i].end(); ++it) {
       int label = it->first;
@@ -1171,11 +1193,6 @@ void VisualizeBBox(const vector<cv::Mat>& images, const Blob<Dtype>* detections,
         cv::Point bottom_right_pt(bboxes[j].xmax(), bboxes[j].ymax());
         cv::rectangle(image, top_left_pt, bottom_right_pt, color, 4);
         cv::Point bottom_left_pt(bboxes[j].xmin(), bboxes[j].ymax());
-        int fontface = cv::FONT_HERSHEY_SIMPLEX;
-        double scale = 1;
-        int thickness = 2;
-        int baseline = 0;
-        char buffer[50];
         snprintf(buffer, sizeof(buffer), "%s: %.2f", label_name.c_str(),
                  bboxes[j].score());
         cv::Size text = cv::getTextSize(buffer, fontface, scale, thickness,