Gabriele Cosmo
127 lines
4.7 KiB
Plaintext
127 lines
4.7 KiB
Plaintext
To add a graphics system:
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1) implement 3 new classes:
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class G4XXX: public G4VGraphicsSystem
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class G4XXXSceneHandler: public G4VSceneHandler
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class G4XXXViewer: virtual public G4VViewer
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These should be placed in their own sub-directory under
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visualization, together with a GNUmakefile and a History file.
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Change the library name G4XXX in "name := G4XXX" in GNUmakefile.
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2) Add to SUBDIRS and SUBLIBS in visualization/GNUmakefile.
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3) Look at the XXX graphics system skeleton in visualization/XXX and
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use it to build your graphics system.
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You might also find it useful to look at ASCIITree (and VTree) as
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an example of a minimal graphics system.
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Look at FukuiRenderer as an example of a system which implements
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AddThis methods for some solids.
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Look at OpenGL as an example of a system which implements a graphical
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database (display lists) and the machinery to decide when to rebuild.
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(OpenGL is complicated by the proliferation of combinations of:
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immediate (no display lists) ) ( X-windows
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stored (uses display lists) ) x ( X with motif - interactive
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( Win32
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(6 combinations) and much use is made of inheritance to avoid code
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duplication.)
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4) If it requires external libraries, introduce two new environment
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variables G4VIS_BUILD_XXX_DRIVER and G4VIS_USE_XXX and make the
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modifications to:
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source/visualization/management/include/MyVisManager.cc
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(similarly all examples vis managers)
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source/visualization/management/src/G4VisManager.cc
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config/G4VIS_BUILD.gmk
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config/G4VIS_USE.gmk
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In any case, augment the informational printing in G4VisManager.cc.
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=========================================================================
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Frequently Asked Questions
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--------------------------
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Q: How do I implement the drawing of markers?
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A: See graphics_reps/include/G4VMarker.hh.
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Q: What functions can a user call?
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A: The interface for the user (application developer) is G4VVisManager
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defined in intercoms/include/G4VVisManager.hh. (The interface
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G4VGraphicsScene in intercoms/include/G4VGraphicsScene.hh is for
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visualization developers only. It is that part of the scene
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handler's interface available to other categories, but must be used
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with care.)
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Q: How do I implement the drawing of trajectories?
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A: (January 2002, referring to Geant4 4.0. There are plans to improve
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the handling of trajectories, so this advice might change.
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Hopefully we'll keep it up to date, but who knows. Be warned.)
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The trajectories themselves have a method,
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G4Trajectory::DrawTrajectory, invoked by the user or by the vis
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manager, if requested, at the end of an event, which calls Draw
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methods of G4VisManager, which call AddPrimitive. So AddPrimitive
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is where you need to look at the vis attributes.
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void G4VisManager::Draw (const G4Polyline& line,
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const G4Transform3D& objectTransform) {
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if (IsValidView ()) {
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ClearTransientStoreIfMarked();
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G4ModelingParameters* pMP = fpSceneHandler -> CreateModelingParameters ();
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G4VModel* pModel = new G4NullModel (pMP);
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fpSceneHandler -> SetModel (pModel);
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fpSceneHandler -> BeginPrimitives (objectTransform);
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fpSceneHandler -> AddPrimitive (line);
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fpSceneHandler -> EndPrimitives ();
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fpSceneHandler -> SetModel (0);
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delete pModel;
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delete pMP;
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}
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}
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It needs to go through the vis manager so that "transients" are
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handled properly. The geometry model and things like axes are
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"run-duration" (sometimes misleadingly called persistent) and
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trajectories, etc., are "end-of-event" (sometimes misleadingly
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called transient) - see G4Scene:
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class G4Scene {
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...
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private:
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G4String fName;
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G4std::vector<G4VModel*> fRunDurationModelList;
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G4std::vector<G4VModel*> fEndOfEventModelList;
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G4VisExtent fExtent;
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G4Point3D fStandardTargetPoint;
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G4bool fRefreshAtEndOfEvent;
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};
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The user can choose to have the view refreshed at the end of event,
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which means previous end-of-event objects get erased. In OpenGL,
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this is done by (a) in Immediate mode, erasing everything and
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redrawing run-duration and the new end-of-event objects or (b) in
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Stored mode, just deleting the display lists of the end-of-event
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objects and recreating them.
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Now, you will see that G4Trajectory::DrawTrajectory is very
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primitive. It has not been changed for years!! It draws lots of
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circles. This is a huge demand on graphical databases and we have
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had on our to-do list for years to introduce AddPrimitive(const
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G4VTrajectory&). Certainly, OpenInventor sags under the weight of
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lots of circles, which it implements as spheres(!), and there are
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great savings of efficiency to be made if graphics systems can
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handle trajectories directly.
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