Add new step graph type to event log visualization tool

webrtc/tools/event_log_visualizer/plot_python.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 47 matching lines @@
             "label=\'%s\')\n",
             i, i, i, i, series_list_[i].label.c_str());
       } else if (series_list_[i].style == LINE_GRAPH) {
         printf("plt.plot(x%zu, y%zu, color=rgb_colors[%zu], label=\'%s\')\n", i,
                i, i, series_list_[i].label.c_str());
       } else if (series_list_[i].style == LINE_DOT_GRAPH) {
         printf(
             "plt.plot(x%zu, y%zu, color=rgb_colors[%zu], label=\'%s\', "
             "marker='.')\n",
             i, i, i, series_list_[i].label.c_str());
+      } else if (series_list_[i].style == LINE_STEP_GRAPH) {
+        // Draw lines from (x[0],y[0]) to (x[1],y[0]) to (x[1],y[1]) and so on
+        // to illustrate the "steps". This can be expressed by duplicating all
+        // elements except the first in x and the last in y.
+        printf("x%zu = [v for dup in x%zu for v in [dup, dup]]\n", i, i);
+        printf("y%zu = [v for dup in y%zu for v in [dup, dup]]\n", i, i);
+        printf(
+            "plt.plot(x%zu[1:], y%zu[:-1], color=rgb_colors[%zu], "
+            "label=\'%s\')\n",
+            i, i, i, series_list_[i].label.c_str());
       } else {
         printf("raise Exception(\"Unknown graph type\")\n");
       }
     }
   }
 
   printf("plt.xlim(%f, %f)\n", xaxis_min_, xaxis_max_);
   printf("plt.ylim(%f, %f)\n", yaxis_min_, yaxis_max_);
   printf("plt.xlabel(\'%s\')\n", xaxis_label_.c_str());
   printf("plt.ylabel(\'%s\')\n", yaxis_label_.c_str());
@@ skipping 18 matching lines @@
 }
 
 Plot* PythonPlotCollection::AppendNewPlot() {
   Plot* plot = new PythonPlot();
   plots_.push_back(std::unique_ptr<Plot>(plot));
   return plot;
 }
 
 }  // namespace plotting
 }  // namespace webrtc