QC-1103 BigScreen Task: create the canvas, paves and labels in configure() (#2148)

mCanvas, mPaves and mLabels are now created just once, during configuration.
Thus, we avoid any issues with republishing mCanvas and making sure it does not delete something already deleted while going 2nd time through initialize() (START STOP START)

Author: knopers8

Modules/Common/src/BigScreen.cxx

@@ -17,9 +17,7 @@
 
 #include "Common/BigScreen.h"
 #include "QualityControl/QcInfoLogger.h"
-#include "QualityControl/MonitorObject.h"
 #include "QualityControl/DatabaseInterface.h"
-#include "QualityControl/ObjectMetadataKeys.h"
 #include "QualityControl/ActivityHelpers.h"
 #include <TDatime.h>
 #include <TPaveText.h>
@@ -35,12 +33,7 @@ namespace o2::quality_control_modules::common
 void BigScreen::configure(const boost::property_tree::ptree& config)
 {
   mConfig = BigScreenConfig(getID(), config);
-}
-
-//_________________________________________________________________________________________
 
-void BigScreen::initialize(quality_control::postprocessing::Trigger t, framework::ServiceRegistryRef services)
-{
   mColors[Quality::Null.getName()] = kViolet - 6;
   mColors[Quality::Bad.getName()] = kRed;
   mColors[Quality::Medium.getName()] = kOrange - 3;
@@ -94,11 +87,18 @@ void BigScreen::initialize(quality_control::postprocessing::Trigger t, framework
 
     index += 1;
   }
-
   mCanvas = std::make_unique<TCanvas>("BigScreen", "QC Big Screen", 800, 600);
   getObjectsManager()->startPublishing(mCanvas.get());
 }
 
+//_________________________________________________________________________________________
+
+void BigScreen::initialize(quality_control::postprocessing::Trigger t, framework::ServiceRegistryRef services)
+{
+  mCanvas->Clear();
+  mCanvas->cd();
+}
+
 //_________________________________________________________________________________________
 // Helper function for retrieving a QualityObject from the QCDB, in the form of a std::pair<std::shared_ptr<QualityObject>, bool>
 // A non-null QO is returned in the first element of the pair if the QO is found in the QCDB