[Common] restored title in quality trending plots (#2259)

The title of the plot was not shown because of the use of a dummy
graph to plot the axes.
The code has been simplified, removing the need of the dummy graph.
The output is visually identical as before, except that the plot title
is now also displayed, and the title of the horizontal axis is "time".

Author: aferrero2707

Modules/Common/include/Common/QualityTask.h

@@ -71,7 +71,6 @@ class QualityTask : public quality_control::postprocessing::PostProcessingInterf
     static std::string trendName(const std::string& groupName, const std::string& qualityName);
 
     std::unique_ptr<TGraph> mGraph;
-    std::unique_ptr<TGraph> mGraphHist;
     std::array<std::unique_ptr<TText>, 4> mLabels;
   };
 
@@ -106,4 +105,4 @@ class QualityTask : public quality_control::postprocessing::PostProcessingInterf
 
 } // namespace o2::quality_control_modules::common
 
-#endif // QUALITYCONTROL_QUALITYTASK_H
+#endif // QUALITYCONTROL_QUALITYTASK_H

Modules/Common/src/QualityTask.cxx

@@ -37,12 +37,13 @@ namespace o2::quality_control_modules::common
 QualityTask::QualityTrendGraph::QualityTrendGraph(std::string name, std::string title) : TCanvas(name.c_str(), title.c_str())
 {
   SetGridy(1);
-  mGraphHist = std::make_unique<TGraph>(0);
 
   mGraph = std::make_unique<TGraph>(0);
+  mGraph->SetTitle(title.c_str());
   mGraph->SetMarkerStyle(kCircle);
-  mGraph->SetTitle(fmt::format("{};time;quality", title).c_str());
+  mGraph->SetTitle(fmt::format("{};time;", title).c_str());
 
+  // add labels in the middle of the vertical axis bins
   mLabels[0] = std::make_unique<TText>(0.09, 0.1 + 0.8 / 8.0, "Null");
   mLabels[1] = std::make_unique<TText>(0.09, 0.1 + 3.0 * 0.8 / 8.0, "Bad");
   mLabels[2] = std::make_unique<TText>(0.09, 0.1 + 5.0 * 0.8 / 8.0, "Medium");
@@ -59,6 +60,10 @@ QualityTask::QualityTrendGraph::QualityTrendGraph(std::string name, std::string
 
 void QualityTask::QualityTrendGraph::update(uint64_t time, Quality q)
 {
+  Clear();
+  cd();
+
+  // set the position of the point based on the value of the quality flag
   float val = 0.5;
   if (q == Quality::Bad) {
     val = 1.5;
@@ -69,33 +74,21 @@ void QualityTask::QualityTrendGraph::update(uint64_t time, Quality q)
   if (q == Quality::Good) {
     val = 3.5;
   }
-  // add new point both the the main graph and to the dummy one used for the axis
-  mGraph->AddPoint(time, val);
-  mGraphHist->AddPoint(time, 0);
 
-  Clear();
-  cd();
+  // add a new point to the graph
+  mGraph->AddPoint(time, val);
 
-  // draw axis
-  mGraphHist->Draw("A");
-
-  // configure and beautify axis
-  auto hAxis = mGraphHist->GetHistogram();
-  hAxis->SetTitle(GetTitle());
-  hAxis->GetXaxis()->SetTimeDisplay(1);
-  hAxis->GetXaxis()->SetNdivisions(505);
-  hAxis->GetXaxis()->SetTimeOffset(0.0);
-  hAxis->GetXaxis()->SetTimeFormat("%Y-%m-%d %H:%M");
-  hAxis->GetYaxis()->SetTitle("");
-  hAxis->GetYaxis()->SetTickLength(0.0);
-  hAxis->GetYaxis()->SetLabelSize(0.0);
-  hAxis->GetYaxis()->SetNdivisions(3, kFALSE);
-  hAxis->SetMinimum(0);
-  hAxis->SetMaximum(4);
-  hAxis->Draw("AXIS");
-
-  // draw main graph
-  mGraph->Draw("PL,SAME");
+  // draw the graph and format the axes
+  mGraph->Draw("APL");
+  mGraph->GetXaxis()->SetTimeDisplay(1);
+  mGraph->GetXaxis()->SetNdivisions(505);
+  mGraph->GetXaxis()->SetTimeOffset(0.0);
+  mGraph->GetXaxis()->SetTimeFormat("%Y-%m-%d %H:%M");
+  mGraph->GetYaxis()->SetTickLength(0.0);
+  mGraph->GetYaxis()->SetLabelSize(0.0);
+  mGraph->GetYaxis()->SetNdivisions(3, kFALSE);
+  mGraph->SetMinimum(0);
+  mGraph->SetMaximum(4);
 
   // draw labels for vertical axis
   for (auto& l : mLabels) {