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.
G4VVisManager
The Visualization Manager is implemented by classes
G4VisManager and G4VisExecutive.
See
"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 (...);
....
}
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.
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
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.
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.
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->GetConstCurrentEvent();
G4SDManager * SDman = G4SDManager::GetSDMpointer();
G4String colNam;
G4int trackerCollID = SDman->GetCollectionID(colNam="TrackerCollection");
G4int calorimeterCollID = SDman->GetCollectionID(colNam="CalCollection");
G4TrajectoryContainer * trajectoryContainer = evt->GetTrajectoryContainer();
G4int n_trajectories = 0;
if(trajectoryContainer)
{ n_trajectories = trajectoryContainer->entries(); }
G4HCofThisEvent * HCE = evt->GetHCofThisEvent();
G4int n_hitCollection = 0;
if(HCE)
{ n_hitCollection = HCE->GetCapacity(); }
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->GetTrajectoryContainer()))[i]->DrawTrajectory();
}
// Construct 3D data for hits
MyTrackerHitsCollection* THC
= (MyTrackerHitsCollection*)(HCE->GetHC(trackerCollID));
if(THC) THC->DrawAllHits();
MyCalorimeterHitsCollection* CHC
= (MyCalorimeterHitsCollection*)(HCE->GetHC(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
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).
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.
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.
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.
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;
}