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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.
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| There are two main components to a widget - the interaction and the representation.
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| ==Interaction==
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| 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.
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| ==Representation==
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| 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.
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| ==Usage==
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| To create the widget:
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| <source lang="cpp">
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| vtkSmartPointer<vtkBoxWidget2> boxWidget =
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| vtkSmartPointer<vtkBoxWidget2>::New();
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| boxWidget->SetInteractor(renderWindowInteractor);
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| </source>
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| 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:
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| <source lang="cpp">
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| vtkSmartPointer<vtkBoxRepresentation> boxRepresentation =
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| vtkSmartPointer<vtkBoxRepresentation>::New();
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| boxWidget->SetRepresentation(boxRepresentation);
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| </source>
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| ==Handling Events==
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| 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.
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| <source lang="cpp">
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| class vtkBoxCallback : public vtkCommand
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| {
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| public:
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| static vtkBoxCallback *New()
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| {
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| return new vtkBoxCallback;
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| }
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|
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| virtual void Execute(vtkObject *caller, unsigned long, void*)
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| {
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|
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| vtkBoxWidget2 *boxWidget =
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| reinterpret_cast<vtkBoxWidget2*>(caller);
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|
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| //get the actual box coordinates/planes
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| vtkSmartPointer<vtkPolyData> polydata =
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| vtkSmartPointer<vtkPolyData>::New();
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| static_cast<vtkBoxRepresentation*>(boxWidget->GetRepresentation())->GetPolyData (polydata);
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|
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| //display one of the points, just so we know it's working
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| double p[3];
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| polydata->GetPoint(0,p);
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| cout << "P: " << p[0] << " " << p[1] << " " << p[2] << endl;
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| }
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| vtkBoxCallback(){}
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|
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| };
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| </source>
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| The Execute function is similar to a vtkCallbackFunction in that the calling object can be obtain by casting "caller" to the appropriate type.
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| ==Putting It All Together==
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| To attach this new class to the widget, instantiate the class and call AddObserver on the widget:
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| <source lang="cpp">
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| vtkSmartPointer<vtkBoxCallback> boxCallback =
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| vtkSmartPointer<vtkBoxCallback>::New();
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|
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| boxWidget->AddObserver(vtkCommand::InteractionEvent,boxCallback);
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| </source>
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| ==Enabling the Widget==
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| Widgets seem fussy about the order that things are done. The following order is appropriate:
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| <source lang="cpp">
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| renderWindow->Render();
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| renderWindowInteractor->Initialize();
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| renderWindow->Render();
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| boxWidget->On();
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|
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| renderWindowInteractor->Start();
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| </source>
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