GenO2Kine: Event-pool developments

Developments needed for event-pool feature, which relies on GenO2Kine for reading from the pool:
- allow reading kine file from Alien
- randomize event picking from file
- possibility to phi-rotate events

https://its.cern.ch/jira/browse/O2-5216

Author: jackal1-66

Generators/include/Generators/GeneratorFromFile.h

@@ -16,6 +16,8 @@
 
 #include "FairGenerator.h"
 #include "Generators/Generator.h"
+#include <TRandom3.h>
+#include <TGrid.h>
 
 class TBranch;
 class TFile;
@@ -94,6 +96,10 @@ class GeneratorFromO2Kine : public o2::eventgen::Generator
   bool mSkipNonTrackable = true; //! whether to pass non-trackable (decayed particles) to the MC stack
   bool mContinueMode = false;    //! whether we want to continue simulation of previously inhibited tracks
   bool mRoundRobin = false;      //! whether we want to take events from file in a round robin fashion
+  bool mRandomize = false;       //! whether we want to randomize the order of events in the input file
+  unsigned int mRngSeed = 0;     //! randomizer seed, 0 for random value
+  bool mRandomPhi = false;       //! whether we want to randomize the phi angle of the particles
+  TGrid* mAlienInstance = nullptr; // a cached connection to TGrid (needed for Alien locations)
 
   std::unique_ptr<o2::dataformats::MCEventHeader> mOrigMCEventHeader; //! the MC event header of the original file
 

Generators/include/Generators/GeneratorFromO2KineParam.h

@@ -25,13 +25,16 @@ namespace eventgen
 /**
  ** a parameter class/struct to keep the settings of
  ** the FromO2Kine event generator and
- ** allow the user to modify them 
+ ** allow the user to modify them
  **/
 
 struct GeneratorFromO2KineParam : public o2::conf::ConfigurableParamHelper<GeneratorFromO2KineParam> {
   bool skipNonTrackable = true;
   bool continueMode = false;
   bool roundRobin = false;   // read events with period boundary conditions
+  bool randomize = false;    // randomize the order of events
+  unsigned int rngseed = 0;  // randomizer seed, 0 for random value
+  bool randomphi = false;    // randomize phi angle
   std::string fileName = ""; // filename to read from - takes precedence over SimConfig if given
   O2ParamDef(GeneratorFromO2KineParam, "GeneratorFromO2Kine");
 };

Generators/src/GeneratorFromFile.cxx

@@ -175,6 +175,13 @@ GeneratorFromO2Kine::GeneratorFromO2Kine(const char* name)
   setPositionUnit(1.);
   setTimeUnit(1.);
 
+  if (strncmp(name, "alien:/", 7) == 0) {
+    mAlienInstance = TGrid::Connect("alien");
+    if (!mAlienInstance) {
+      LOG(fatal) << "Could not connect to alien, did you check the alien token?";
+      return;
+    }
+  }
   mEventFile = TFile::Open(name);
   if (mEventFile == nullptr) {
     LOG(fatal) << "EventFile " << name << " not found";
@@ -210,6 +217,12 @@ bool GeneratorFromO2Kine::Init()
   mSkipNonTrackable = param.skipNonTrackable;
   mContinueMode = param.continueMode;
   mRoundRobin = param.roundRobin;
+  mRandomize = param.randomize;
+  mRngSeed = param.rngseed;
+  mRandomPhi = param.randomphi;
+  if (mRandomize) {
+    gRandom->SetSeed(mRngSeed);
+  }
 
   return true;
 }
@@ -229,6 +242,18 @@ bool GeneratorFromO2Kine::importParticles()
   // It might need some adjustment to make it work with secondaries or to continue
   // from a kinematics snapshot
 
+  // Randomize the order of events in the input file
+  if (mRandomize) {
+    mEventCounter = gRandom->Integer(mEventsAvailable);
+  }
+
+  double dPhi = 0.;
+  // Phi rotation
+  if (mRandomPhi) {
+    dPhi = gRandom->Uniform(2 * TMath::Pi());
+    LOG(info) << "Rotating phi by " << dPhi;
+  }
+
   if (mEventCounter < mEventsAvailable) {
     int particlecounter = 0;
 
@@ -253,6 +278,15 @@ bool GeneratorFromO2Kine::importParticles()
       auto pdg = t.GetPdgCode();
       auto px = t.Px();
       auto py = t.Py();
+      if (mRandomPhi) {
+        // transformation applied through rotation matrix
+        auto cos = TMath::Cos(dPhi);
+        auto sin = TMath::Sin(dPhi);
+        auto newPx = px * cos - py * sin;
+        auto newPy = px * sin + py * cos;
+        px = newPx;
+        py = newPy;
+      }
       auto pz = t.Pz();
       auto vx = t.Vx();
       auto vy = t.Vy();