A GLAST Geant4 Visualization Howto (Windows based)

In order to clarify the step I've followed to enable visualization drivers on Geant4 for the beamtest06 package on my windows box I've decided to setup this small howto page; I hope it can be of some use for GLAST. Please for any comments and/or requests contact me. Please note that these instructions are for Geant4 6.2.2; I expect that some changes will occur for the new 8.0 version (for example Francesco told me that in the new version you don't need anymore to register individual drivers, you just setup a visualization manager and have at your disposal all the possible visualization output).

Please note also that almost the same thing can be done for our standard G4Generator package; we just need to register a visualization manager using our customized RunManager and than pass, with the use of the standard jobOptions file, to Geant4 some UI macros like the one I show down in the section 3 of this page. I've not tried it, but it should be trivia. In this way we could have G4Generator generates HepRep files (or VRML, or DAWN, or what you want) directly. Consider that the output of Geant4 is quite different, as volumes hierarchy, from the one we are used in GlastDetSvc. For example the HepRep file that Geant4 generates contains only polygons; so any box is splitted in 6 polygons and the InstanceTree in the generated HepRep file will be quite big (and different from the HepRep file generated by HepRepSvc).

1. Building the proper Geant4 external library

First of all we need a proper Geant4 library. In our standard distribution of Geant4 we have left out the visualization modules .. to reintroduce them on windows I've just got the really useful Geant4build package by Tracy and modified the requirements it in the following way:

in the include_dirs definition I've added

 "$(G4srcdir)/visualization/management/include" \



             "$(G4srcdir)/visualization/FukuiRenderer/include" \



             "$(G4srcdir)/visualization/HepRep/include" \



             "$(G4srcdir)/visualization/HepRep/include/zlib" \



             "$(G4srcdir)/visualization/HepRep/include/zipios++" \



             "$(G4srcdir)/visualization/HepRep/include/ref" \



             "$(G4srcdir)/visualization/HepRep/include/HEPREP" \



             "$(G4srcdir)/visualization/RayTracer/include" \



             "$(G4srcdir)/visualization/VRML/include" \



             "$(G4srcdir)/visualization/Tree/include" \



             "$(G4srcdir)/visualization/XXX/include" \



             "$(G4srcdir)/visualization/modeling/include"

I've added the following library in the constituents

 library libG4visualization    -no_share \



     
           
-s=$(G4srcdir)/visualization/modeling $(source) \



     
           
-s=$(G4srcdir)/visualization/management $(source) \



     
           
-s=$(G4srcdir)/visualization/FukuiRenderer $(source) \



     
           
-s=$(G4srcdir)/visualization/HepRep $(source) \



     
           
-s=$(G4srcdir)/visualization/RayTracer $(source) \



                  -s=$(G4srcdir)/visualization/VRML $(source) \



                  -s=$(G4srcdir)/visualization/Tree $(source) \



                  -s=$(G4srcdir)/visualization/XXX $(source)

With these changes I've managed to build the Geant4 library with all the standard libraries plus the libG4visualization one .. if you need it I've just put a precompiled version here.

2. Changes to IExternal/Geant4 package

At this point you need to change the IExternal/Geant4 package by adding in the requirements file to the macro_append Geant4_linkopts the new libG4visualization library.

3. Changes to the beam test package

In the end you need some changes to the beamtest06 package. For example, if you want to add the HepRep visualization driver

Add to the requirements file the flag /D G4VIS_USE to the cpp_flags for the package
Add to the VisManager.cxx file something like

#include "G4HepRepFile.hh"

        #include "G4HepRep.hh"

Add to the constructor of the VisManager class something like

        RegisterGraphicsSystem (new G4HepRep);

At this point you can use a standard Geant4 visualization macro like this one

  /vis/open HepRepFile


  /vis/viewer/reset


  /vis/viewer/set/viewpointThetaPhi 0 0 deg


  /vis/viewer/zoom 1.3


  /vis/scene/add/axes      0 0 0 50 mm


  /vis/scene/endOfEventAction accumulate


  /tracking/storeTrajectory 1


  /vis/drawVolume


  /vis/scene/add/trajectories

to setup the proper generation of an HepRep file that you can than visualize with Wired or FRED.