Implementation example: Plot3D presentation

This section describes how a FIELDS presentation is implemented using Plot3D presentation as an example.

General description of Plot3D presentation

Plot3D is a presentation of scalar values of meshes lying on a cutting plane. The relief and coloring of the resulting presentation both correspond to the values applied to the cells of a mesh.

In general this presentation can be built using the following sequence of the ParaVis filters:

MedReadear -> Slice -> Calculator -> WarpByScalar

  • MedReadear is used to read a MED file.

  • Slice filter defines a cutting plane within the 3D mesh, on the basis of which the relief presentation is built. This plane is a 2D mesh with values (scalar or vector) applied to the cells of a plane. If initial mesh is a 2D mesh, then Slice filter is unnecessary.

  • Calculator filter converts vector values on cells to the scalar values. In case of scalar values Calculator filter is unnecessary.

  • Finally, WarpByScalar filter is applied to the 2D mesh with scalar values on cells to build colored relief presentation.

Currently, only two parameters can be changed for this type of presentation, namely:

  • Position of a cutting plane allows selecting the position of the cutting plane within the bounding box of a mesh (ranging from 0 to 1). This it is a property of Slice filter.

  • Cutting plane normal allows specifying an orientation of the cut plane in 3D space. This is also a property of Slice filter.

All other parameters are inherited from the parent presentation class.

GUI controls

First step consists in implementing the corresponging GUI controls. This step includes the following actions:

  • Add needed controls to UI using Qt Designer

    _images/image_ui_designer_prs_panel.png

  • Implement C++ wrappings for newly created GUI controls and add corresponding signal-slot connections: see code.

  • Add new types of events into PresentationEvent.hxx file:

    ...
EVENT_VIEW_OBJECT_PLOT3D,
...
EVENT_CHANGE_NORMAL,
EVENT_CHANGE_PLANE_POS,

  • Implement MEDWidgetHelperPlot3D class. This class sends events to PresentationController on each user action in the Presentation Parameters panel and updates a content of the Presentation Parameters panel in case if changes in a presentation were made, via the medcalc Python API.

  • Modify PresentationController class. This class is used to add items into the Presentations menu and toolbar, and to translate GUI events into the medcalc Python API: see code.

Extend MEDCALC::MEDPresentationManager

Next step consists in extending of the MEDCALC::MEDPresentationManager CORBA service; it assumes the following actions:

  • Extend MEDPresentationManager IDL interface.

  • Implement methods, declared in the IDL interface.

Extend medcalc API

Next step consists in extending medcalc Python API, by adding functions to make and update Plot3D presentation and retrieve parameters of Plot3D presentations.

Implement pipeline

Final step consists in building the pipeline, described above, in the frames of the MEDPresentationPlot3D class.