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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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               examples/extended/visualization/standalone
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This example illustrates how one might use the Geant4 Visualization
System as a "stand alone" graphics library and viewer.  It makes use
of the "user action" feature of the Geant4 vis manager - for a fuller
example of the use of this feature see
examples/extended/visualization/userVisAction.

1) Define a G4VUserVisAction that implements a Draw method.  An
   example is provided - see StandaloneVisAction.hh/cc.
   StandaloneVisAction::Draw illustrates:
   a) a simple box;
   b) a Boolean solid;
   c) an alternative way of drawing a solid by obtaining the
      polyhedral representation.
   The last is included for interest, not as a recommendation.
      
2) In the main program, StandaloneVisAction must be instantiated and
   its pointer registered with the visualization manager. You may
   optionally specify an extent at this point to assist the viewers to
   locate the objects.

3) To visualise, use the usual Geant4 vis commands to create a view
   and scene, then add the vis action to the scene, optionally with an
   extent - see standalone.mac.

Note: The system needs an "extent" in order to point the virtual
camera and adjust its field of view, etc.  This defines the "standard
view".  You may zoom, etc., from this standard view.  The extent may
be specified as suggested above or by using /vis/scene/add/extent.


John Allison
27th November 2014