This example demonstrates VTK visualisation driver. The code is based on the basic/B1 example, although the geometry has been modified. The physical example is a concerete dump, so a cuboid with a cylindrical hole removed.

VTK is a graphical pipeline (https://book.vtk.org/en/latest/VTKBook/04Chapter4.html#pipeline-design-and-implementation) based renderer.

VTK has some visualisation commands which are not applicable to all viewers, which currently include cutters, clippers and geometry overlays. The VTK commands are in vtk.mac and you can explore apply different VTK only commands.

A- VISUALISATION

This example is really for demonstration of VTK and so the easiest way to start with

% G4VIS_DEFAULT_DRIVER=VtkQt ./exampleVtk

or

% G4UI_USE_TCSH=1 G4VIS_DEFAULT_DRIVER=VtkNative ./exampleVtk

The event loop for the UI can be blocked by the VtkNative window. So if input events are captured by VTK, then the easiest way to exit from the viewer is to hit the 'q' button, then you are returned to the shell UI. To restart interaction then issue the command

Idle> /vis/vtk/startInteractor

B- USER INTERFACES

VTK can be used in conjunction with all UI systems. If a shell UI is used event loop for the UI can be blocked by the VtkNative window. So if input events are captured by VTK, then the easiest way to exit from the viewer is to hit the 'q' button, then you are returned to the shell UI. To restart interaction then issue the command

Idle> /vis/vtk/startInteractor

C- HOW TO RUN

Starting with VTK

% G4VIS_DEFAULT_DRIVER=VtkQt ./exampleVtk

Executing VTK specific commands

Idle> /control/execute vtk.mac

There are various pipelines and the state of the pipelines can be displayed by issuing this command

/vis/vtk/printDebug

Pipelines can be switched during operation. This is performed by calling

/vis/vtk/set/polyhedronPipeline (append/tensor/bake/separate)

and then a subsequent

/vis/viewer/flush

There is significantly different performance between these pipelines. Append, tensor and bake are all designed for large models and high performance. Separate creates a pipeline for each polyhedron, each pipeline will ultimately end with a draw call. In general with modern pipelined shaders draw calls should be kept to a minimum.

For debugging the VTK viewer it is possible to place a head up display (HUD) which gives key information on the viewer performance. The HUD is enabled by issuing

/vis/vtk/set/hud 1

Stewart Boogert 7th November 2023