Difference between revisions of "VTK/Tutorials/Widgets"

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==Introduction==
= '''Examples are now hosted here: [https://kitware.github.io/vtk-examples/site/ VTKExamples website].''' =
A widget is an object that provides an interface to a complex operation. For example, vtkBoxWidget2 allows you to move a box around a scene. It provides a way to translate the box, rotate the box, and scale the box. Of course this can all be achieved using a vtkCubeSource and a specialized vtkInteractorStyle, but the widget provides all of this in a "canned" way.
 
Consider referencing the [[ VTK/Examples/Cxx#Widgets | Widgets examples page ]] for more examples.
 
There are two main components to a widget - the interaction and the representation.
 
==Interaction==
The "interaction" is the class named vtk*Widget (for example, vtkBoxWidget2). It contains all of the options for the interaction, as well as the event handling.
 
==Representation==
The representation is the object that is drawn and interacted with. The class is named vtk*Representation, where the * is the same * from vtk*Widget.
 
==Usage==
To create the widget:
<source lang="cpp">
  vtkSmartPointer<vtkBoxWidget2> boxWidget =
    vtkSmartPointer<vtkBoxWidget2>::New();
  boxWidget->SetInteractor(renderWindowInteractor);
</source>
 
Most widgets will create a default representation automatically. If you wish to use several non-defaults, you should probably create the representation manually, and tell the widget to use it:
<source lang="cpp"> 
  vtkSmartPointer<vtkBoxRepresentation> boxRepresentation =
      vtkSmartPointer<vtkBoxRepresentation>::New();
  boxWidget->SetRepresentation(boxRepresentation);
</source> 
 
==Handling Events==
Often you will want to do something in response to the user interacting with the widget. To do this, you should create a subclass of vtkCommand. The Execute function does the work.
 
<source lang="cpp"> 
class vtkBoxCallback : public vtkCommand
{
  public:
    static vtkBoxCallback *New()
    {
      return new vtkBoxCallback;
    }
   
    virtual void Execute(vtkObject *caller, unsigned long, void*)
    {
     
      vtkBoxWidget2 *boxWidget =
          reinterpret_cast<vtkBoxWidget2*>(caller);
     
      //get the actual box coordinates/planes
      vtkSmartPointer<vtkPolyData> polydata =
          vtkSmartPointer<vtkPolyData>::New();
      static_cast<vtkBoxRepresentation*>(boxWidget->GetRepresentation())->GetPolyData (polydata);
     
      //display one of the points, just so we know it's working
      double p[3];
      polydata->GetPoint(0,p);
      cout << "P: " << p[0] << " " << p[1] << " " << p[2] << endl;
    }
    vtkBoxCallback(){}
   
};
</source> 
 
The Execute function is similar to a vtkCallbackFunction in that the calling object can be obtained by casting "caller" to the appropriate type.
 
==Putting It All Together==
To attach this new class to the widget, instantiate the class and call AddObserver on the widget:
 
<source lang="cpp"> 
  vtkSmartPointer<vtkBoxCallback> boxCallback =  
      vtkSmartPointer<vtkBoxCallback>::New();
  boxWidget->AddObserver(vtkCommand::InteractionEvent,boxCallback);
</source> 
 
==Enabling the Widget==
Widgets seem fussy about the order that things are done. The following order is appropriate:
<source lang="cpp"> 
  renderWindow->Render();
  renderWindowInteractor->Initialize();
  renderWindow->Render();
 
  boxWidget->On();
 
  renderWindowInteractor->Start();
 
</source>

Latest revision as of 10:03, 22 December 2020

Examples are now hosted here: VTKExamples website.