| Geant4 User's Guide For Application Developers Visualization

8.5 Controlling Visualization from Compiled Code

While a Geant4 simulation is running, visualization can be performed without user intervention. This is accomplished by calling methods of the Visualization Manager from methods of the user action classes (G4UserRunAction and G4UserEventAction, for example). In this section methods of the class G4VVisManager, which is part of the `graphics_reps` category, are described and examples of their use are given.

#### 8.5.1 Class G4VVisManager

The Visualization Manager is implemented by classes G4VisManager and G4VisExecutive. See Section 8.2 "Making a Visualization Executable". In order that your Geant4 be compilable either with or without the visualization category, you should not use these classes directly in your C++ source code, other than in the `main()` function. Instead, you should use their abstract base class G4VVisManager, defined in the `intercoms` category.

The pointer to the concrete instance of the real Visualization Manager can be obtained as follows:

      //----- Getting a pointer to the concrete Visualization Manager instance
      G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();

The method `G4VVisManager::GetConcreteInstance()` returns `NULL` if Geant4 is not ready for visualization. Thus your C++ source code should be protected as follows:

      //----- How to protect your C++ source codes in visualization
      if (pVVisManager) {
          ....
          pVVisManager ->Draw (...);
          ....
      }

#### 8.5.2 Visualization of detector components

If you have already constructed detector components with logical volumes to which visualization attributes are properly assigned, you are almost ready for visualizing detector components. All you have to do is to describe proper visualization commands within your C++ codes, using the `ApplyCommand()` method.

For example, the following is sample C++ source codes to visualize the detector components:

      //----- C++ source code: How to visualize detector components (2)
      //                       ... using visualization commands in source codes

      G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance() ;

      if(pVVisManager)
      {
          ... (camera setting etc) ...
          G4UImanager::GetUIpointer()->ApplyCommand("/vis/drawVolume");
          G4UImanager::GetUIpointer()->ApplyCommand("/vis/viewer/flush");
      }

      //-----  end of C++ source code

In the above, you should also describe `/vis/open` command somewhere in your C++ codes or execute the command from (G)UI at the executing stage.

#### 8.5.3 Visualization of trajectories

In order to visualize trajectories, you can use the method `void G4Trajectory::DrawTrajectory()` defined in the tracking category. In the implementation of this method, the following drawing method of G4VVisManager is used:

        //----- A drawing method of G4Polyline
        virtual void G4VVisManager::Draw (const G4Polyline&, ...) ;

The real implementation of this method is described in the class G4VisManager.

At the end of one event, a set of trajectories can be stored as a list of G4Trajectory objects. Therefore you can visualize trajectories, for example, at the end of each event, by implementing the method `MyEventAction::EndOfEventAction()` as follows:

      //----- C++ source codes
      void ExN03EventAction::EndOfEventAction(const G4Event* evt)
      {
        .....
        // extract the trajectories and draw them
        if (G4VVisManager::GetConcreteInstance())
          {
           G4TrajectoryContainer* trajectoryContainer = evt->GetTrajectoryContainer();
           G4int n_trajectories = 0;
           if (trajectoryContainer) n_trajectories = trajectoryContainer->entries();

           for (G4int i=0; i < n_trajectories; i++)
              { G4Trajectory* trj=(G4Trajectory*)((*(evt->GetTrajectoryContainer()))[i]);
                if (drawFlag == "all") trj->DrawTrajectory(50);
                else if ((drawFlag == "charged")&&(trj->GetCharge() != 0.))
                                        trj->DrawTrajectory(50);
                else if ((drawFlag == "neutral")&&(trj->GetCharge() == 0.))
                                        trj->DrawTrajectory(50);
              }
        }
      }
      //----- end of C++ source codes

#### 8.5.4 Enhanced trajectory drawing

It is possible to use the enhanced trajectory drawing functionality in compiled code as well as from commands. Multiple trajectory models can be instantiated, configured and registered with G4VisManager. For details, see the section on Enhanced Trajectory Drawing.

#### 8.5.5 HepRep Attributes for Trajectories

The HepRep file formats, HepRepFile and HepRepXML, attach various attributes to trajectories such that you can view these attributes, label trajectories by these attributes or make visibility cuts based on these attributes. If you use the default Geant4 trajectory class, from /tracking/src/G4Trajectory.cc, available attributes will be:

- Track ID
- Parent ID
- Particle Name
- Charge
- PDG Encoding
- Momentum 3-Vector
- Momentum magnitude
- Number of points

You can add additional attributes of your choosing by modifying the relevant part of G4Trajectory (look for the methods GetAttDefs and CreateAttValues). If you are using your own trajectory class, you may want to consider copying these methods from G4Trajectory.

#### 8.5.6 Visualization of hits

Hits are visualized with classes G4Square or G4Circle, or other user-defined classes inheriting the abstract base class G4VMarker. Drawing methods for hits are not supported by default. Instead, ways of their implementation are guided by virtual methods, `G4VHit::Draw()` and `G4VHitsCollection::DrawAllHits()`, of the abstract base classes G4VHit and G4VHitsCollection. These methods are defined as empty functions in the `digits+hits` category. You can overload these methods, using the following drawing methods of class G4VVisManager, in order to visualize hits:

      //----- Drawing methods of G4Square and G4Circle
      virtual void G4VVisManager::Draw (const G4Circle&, ...) ;
      virtual void G4VVisManager::Draw (const G4Square&, ...) ;

The real implementations of these `Draw()` methods are described in class G4VisManager.

The overloaded implementation of `G4VHits::Draw()` will be held by, for example, class MyTrackerHits inheriting G4VHit as follows:

      //----- C++ source codes: An example of giving concrete implementation of
      //       G4VHit::Draw(), using  class MyTrackerHit : public G4VHit {...}
      //
     void MyTrackerHit::Draw()
     {
        G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();
        if(pVVisManager)
        {
          // define a circle in a 3D space
          G4Circle circle(pos);
          circle.SetScreenSize(0.3);
          circle.SetFillStyle(G4Circle::filled);

          // make the circle red
          G4Colour colour(1.,0.,0.);
          G4VisAttributes attribs(colour);
          circle.SetVisAttributes(attribs);

          // make a 3D data for visualization
          pVVisManager->Draw(circle);
        }
      }

      //----- end of C++ source codes

The overloaded implementation of `G4VHitsCollection::DrawAllHits()` will be held by, for example, class MyTrackerHitsCollection inheriting class G4VHitsCollection as follows:

      //----- C++ source codes: An example of giving concrete implementation of
      //       G4VHitsCollection::Draw(),
      //       using  class MyTrackerHit : public G4VHitsCollection{...}
      //
      void MyTrackerHitsCollection::DrawAllHits()
      {
        G4int n_hit = theCollection.entries();
        for(G4int i=0;i < n_hit;i++)
        {
          theCollection[i].Draw();
        }
      }

      //----- end of C++ source codes

Thus, you can visualize hits as well as trajectories, for example, at the end of each event by implementing the method `MyEventAction::EndOfEventAction()` as follows:

      void MyEventAction::EndOfEventAction()
      {
        const G4Event* evt = fpEventManager->get_const_currentEvent();

        G4SDManager * SDman = G4SDManager::get_SDMpointer();
        G4String colNam;
        G4int trackerCollID = SDman->get_collectionID(colNam="TrackerCollection");
        G4int calorimeterCollID = SDman->get_collectionID(colNam="CalCollection");

        G4TrajectoryContainer * trajectoryContainer = evt->get_trajectoryContainer();
        G4int n_trajectories = 0;
        if(trajectoryContainer)
        { n_trajectories = trajectoryContainer->entries(); }

        G4HCofThisEvent * HCE = evt->get_HCofThisEvent();
        G4int n_hitCollection = 0;
        if(HCE)
        { n_hitCollection = HCE->get_capacity(); }

        G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();

        if(pVVisManager)
        {

          // Declare begininng of visualization
          G4UImanager::GetUIpointer()->ApplyCommand("/vis/scene/notifyHandlers");

          // Draw trajectories
          for(G4int i=0; i < n_trajectories; i++)
          {
              (*(evt->get_trajectoryContainer()))[i]->DrawTrajectory();
          }

          // Construct 3D data for hits
          MyTrackerHitsCollection* THC
            = (MyTrackerHitsCollection*)(HCE->get_HC(trackerCollID));
          if(THC) THC->DrawAllHits();
          MyCalorimeterHitsCollection* CHC
            = (MyCalorimeterHitsCollection*)(HCE->get_HC(calorimeterCollID));
          if(CHC) CHC->DrawAllHits();

          // Declare end of visualization
          G4UImanager::GetUIpointer()->ApplyCommand("/vis/viewer/update");

        }

      }

      //----- end of C++ codes

You can re-visualize a physical volume, where a hit is detected, with a highlight color, in addition to the whole set of detector components. It is done by calling a drawing method of a physical volume directly. The method is:

      //----- Drawing methods of a physical volume
      virtual void Draw (const G4VPhysicalVolume&, ...) ;

This method is, for example, called in a method `MyXXXHit::Draw()`, describing the visualization of hits with markers. The following is an example for this:

      //----- C++ source codes: An example of visualizing hits with
      void MyCalorimeterHit::Draw()
      {
        G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();
        if(pVVisManager)
        {
          G4Transform3D trans(rot,pos);
          G4VisAttributes attribs;
          G4LogicalVolume* logVol = pPhys->GetLogicalVolume();
          const G4VisAttributes* pVA = logVol->GetVisAttributes();
          if(pVA) attribs = *pVA;
          G4Colour colour(1.,0.,0.);
          attribs.SetColour(colour);
          attribs.SetForceSolid(true);

          //----- Re-visualization of a selected physical volume with red color
          pVVisManager->Draw(*pPhys,attribs,trans);

        }
      }

      //----- end of C++ codes

#### 8.5.7 HepRep Attributes for Hits

The HepRep file formats, HepRepFile and HepRepXML, attach various attributes to hits such that you can view these attributes, label trajectories by these attributes or make visibility cuts based on these attributes. Examples of adding HepRep attributes to hit classes can be found in examples /extended/analysis/A01 and /extended/runAndEvent/RE01.

For example, in example RE01's class RE01CalorimeterHit.cc, available attributes will be:

- Hit Type
- Track ID
- Z Cell ID
- Phi Cell ID
- Energy Deposited
- Energy Deposited by Track
- Position
- Logical Volume

You can add additional attributes of your choosing by modifying the relevant part of the hit class (look for the methods GetAttDefs and CreateAttValues).

#### 8.5.8 Visualization of text

In Geant4 Visualization, a text, i.e., a character string, is described by class G4Text inheriting G4VMarker as well as G4Square and G4Circle. Therefore, the way to visualize text is the same as for hits. The corresponding drawing method of G4VVisManager is:

      //----- Drawing methods of G4Text
      virtual void G4VVisManager::Draw (const G4Text&, ...);

The real implementation of this method is described in class G4VisManager.

#### 8.5.9 Visualization of polylines and tracking steps

Polylines, i.e., sets of successive line segments, are described by class G4Polyline. For G4Polyline, the following drawing method of class G4VVisManager is prepared:

       //----- A drawing method of G4Polyline
        virtual void G4VVisManager::Draw (const G4Polyline&, ...) ;

The real implementation of this method is described in class G4VisManager.

Using this method, C++ source codes to visualize G4Polyline are described as follows:

     //----- C++ source code: How to visualize a polyline
      G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();

      if (pVVisManager) {
          G4Polyline polyline ;

          ..... (C++ source codes to set vertex positions, color, etc)

          pVVisManager -> Draw(polyline);

      }

      //----- end of C++ source codes

Tracking steps are able to be visualized based on the above visualization of G4Polyline. You can visualize tracking steps at each step automatically by writing a proper implementation of class MySteppingAction inheriting G4UserSteppingAction, and also with the help of the Run Manager.

First, you must implement a method, `MySteppingAction::UserSteppingAction()`. A typical implementation of this method is as follows:

      //----- C++ source code: An example of visualizing tracking steps
      void MySteppingAction::UserSteppingAction()
      {
          G4VVisManager* pVVisManager = G4VVisManager::GetConcreteInstance();

          if (pVVisManager) {

            //----- Get the Stepping Manager
            const G4SteppingManager* pSM = GetSteppingManager();

    	//----- Define a line segment
            G4Polyline polyline;
            G4double charge = pSM->GetTrack()->GetDefinition()->GetPDGCharge();
            G4Colour colour;
            if      (charge < 0.) colour = G4Colour(1., 0., 0.);
            else if (charge < 0.) colour = G4Colour(0., 0., 1.);
            else                  colour = G4Colour(0., 1., 0.);
            G4VisAttributes attribs(colour);
            polyline.SetVisAttributes(attribs);
            polyline.push_back(pSM->GetStep()->GetPreStepPoint()->GetPosition());
            polyline.push_back(pSM->GetStep()->GetPostStepPoint()->GetPosition());

    	//----- Call a drawing method for G4Polyline
            pVVisManager -> Draw(polyline);

          }
      }

      //----- end of C++ source code

Next, in order that the above C++ source code works, you have to pass the information of the MySteppingAction to the Run Manager in the `main()` function:

      //----- C++ source code: Passing what to do at each step to the Run Manager

      int main()
      {
         ...

         // Run Manager
         G4RunManager * runManager = new G4RunManager;

         // User initialization classes
         ...
         runManager->SetUserAction(new MySteppingAction);
         ...
      }

      //----- end of C++ source code

Thus you can visualize tracking steps with various visualization attributes, e.g., color, at each step, automatically.

As well as tracking steps, you can visualize any kind 3D object made of line segments, using class G4Polyline and its drawing method, defined in class G4VVisManager. See, for example, the implementation of the `/vis/scene/add/axes` command.

#### 8.5.10 Visualization User Action

You can implement the `Draw` method of `G4VUserVisAction`, e.g., the class definition could be:

    class StandaloneVisAction: public G4VUserVisAction {
      void Draw();
    };

and the implementation:

    void StandaloneVisAction::Draw() {
      G4VVisManager* pVisManager = G4VVisManager::GetConcreteInstance();
      if (pVisManager) {

        // Simple box...
        pVisManager->Draw(G4Box("box",2*m,2*m,2*m),
    		      G4VisAttributes(G4Colour(1,1,0)));

        // Boolean solid...
        G4Box boxA("boxA",3*m,3*m,3*m);
        G4Box boxB("boxB",1*m,1*m,1*m);
        G4SubtractionSolid subtracted("subtracted_boxes",&boxA,&boxB,
                           G4Translate3D(3*m,3*m,3*m));
        pVisManager->Draw(subtracted,
                          G4VisAttributes(G4Colour(0,1,1)),
                          G4Translate3D(6*m,6*m,6*m));
      }
    }

Explicit use of polyhedron objects is equivalent, e.g.:

        // Same, but explicit polyhedron...
        G4Polyhedron* pA = G4Box("boxA",3*m,3*m,3*m).CreatePolyhedron();
        G4Polyhedron* pB = G4Box("boxB",1*m,1*m,1*m).CreatePolyhedron();
        pB->Transform(G4Translate3D(3*m,3*m,3*m));
        G4Polyhedron* pSubtracted = new G4Polyhedron(pA->subtract(*pB));
        G4VisAttributes subVisAtts(G4Colour(0,1,1));
        pSubtracted->SetVisAttributes(&subVisAtts);
        pVisManager->Draw(*pSubtracted,G4Translate3D(6*m,6*m,6*m));
        delete pA;
        delete pB;
        delete pSubtracted;

If efficiency is an issue, create the objects in the constructor, delete them in the destructor and draw them in your `Draw` method. Anyway, an instance of your class needs to be registered with the vis manager, e.g.:

      ...
      G4VisManager* visManager = new G4VisExecutive;
      visManager->Initialize ();

      visManager->SetUserAction
        (new StandaloneVisAction,
         G4VisExtent(-5*m,5*m,-5*m,5*m,-5*m,5*m));  // 2nd argument optional.
      ...

then activate by adding to a scene, e.g:

    /control/verbose 2
    /vis/verbose c
    /vis/open OGLSXm
    /vis/scene/create
    #/vis/scene/add/userAction
    /vis/scene/add/userAction -10 10 -10 10 -10 10 m
    #/vis/scene/add/axes 0 0 0 10 m
    #/vis/scene/add/scale 10 m
    /vis/sceneHandler/attach
    /vis/viewer/refresh

The extent can be added on registration or on the command line or neither (if the extent of the scene is set by other components). Your `Draw` method will be called whenever needed to refresh the screen or rebuild a graphics database, for any chosen viewer. The scene can be attached to any scene handler and your drawing will be shown.

#### 8.5.11 Standalone Visualization

The above raises the possibility of using Geant4 as a "standalone" graphics package without invoking the run manager. The following main program, together with a user visualization action and a macro file, will allow you to view your drawing interactively on any of the supported graphics systems.

    #include "globals.hh"
    #include "G4VisExecutive.hh"
    #include "G4VisExtent.hh"
    #include "G4UImanager.hh"
    #include "G4UIterminal.hh"
    #include "G4UItcsh.hh"

    #include "StandaloneVisAction.hh"

    int main() {

      G4VisManager* visManager = new G4VisExecutive;
      visManager->Initialize ();

      visManager->SetUserAction
        (new StandaloneVisAction,
         G4VisExtent(-5*m,5*m,-5*m,5*m,-5*m,5*m));  // 2nd argument optional.

      G4UImanager* UI = G4UImanager::GetUIpointer ();
      UI->ApplyCommand ("/control/execute standalone.g4m");

      G4UIsession* session = new G4UIterminal(new G4UItcsh);
      session->SessionStart();

      delete session;
      delete visManager;
    }

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