Improve compass widget example

src/Cxx/Widgets/CompassWidget.cxx

-#include <vtkActor.h>
-#include <vtkArrowSource.h>
+#include <vtkAnnotatedCubeActor.h>
+#include <vtkCamera.h>
+#include <vtkCommand.h>
 #include <vtkCompassRepresentation.h>
 #include <vtkCompassWidget.h>
-#include <vtkInteractorStyleTrackball.h>
-#include <vtkInteractorStyleTrackballCamera.h>
 #include <vtkNamedColors.h>
 #include <vtkNew.h>
-#include <vtkPolyData.h>
-#include <vtkPolyDataMapper.h>
 #include <vtkProperty.h>
 #include <vtkRenderWindow.h>
 #include <vtkRenderWindowInteractor.h>
 #include <vtkRenderer.h>
 
-int main(int, char*[])
+#if VTK_VERSION_NUMBER >= 90220220831ULL
+#define VTK_HAS_IMPROVED_COMPASSWIDGETREPRESENTATION 1
+#endif
+
+class vtkICWValueChangedCallback : public vtkCommand
 {
-  vtkNew<vtkNamedColors> colors;
+public:
+  static vtkICWValueChangedCallback* New()
+  {
+    return new vtkICWValueChangedCallback();
+  }
+  virtual void Execute(vtkObject* caller, unsigned long vtkNotUsed(eventId),
+                       void* vtkNotUsed(callData))
+  {
+    vtkCompassWidget* widget = vtkCompassWidget::SafeDownCast(caller);
+    vtkCamera* camera = widget->GetCurrentRenderer()->GetActiveCamera();
 
-  vtkNew<vtkArrowSource> arrowSource;
+    // calculate new camera position from compass widget parameters
+    double distance = widget->GetDistance();
+    double tilt = widget->GetTilt();
+    double heading = widget->GetHeading();
 
-  vtkNew<vtkPolyDataMapper> mapper;
-  mapper->SetInputConnection(arrowSource->GetOutputPort());
+    double pos[3] = {0, 0, 0};
+    pos[0] = distance * cos(vtkMath::RadiansFromDegrees(heading)) *
+        cos(vtkMath::RadiansFromDegrees(tilt));
+    pos[1] = distance * sin(vtkMath::RadiansFromDegrees(heading)) *
+        cos(vtkMath::RadiansFromDegrees(tilt));
+    pos[2] = distance * sin(vtkMath::RadiansFromDegrees(tilt));
 
-  vtkNew<vtkActor> actor;
-  actor->SetMapper(mapper);
-  actor->GetProperty()->SetColor(colors->GetColor3d("PeachPuff").GetData());
+    camera->SetPosition(pos);
+    camera->SetFocalPoint(0, 0, 0);
+    camera->SetViewUp(0, 0, 1);
+    camera->SetClippingRange(0.1, distance + 1);
+
+    widget->GetCurrentRenderer()->Render();
+  }
+  vtkICWValueChangedCallback()
+  {
+  }
+};
+
+int main(int, char*[])
+{
+  vtkNew<vtkNamedColors> colors;
+
+  // a cube with text on its faces
+  vtkNew<vtkAnnotatedCubeActor> actor;
+  actor->GetTextEdgesProperty()->SetColor(
+      colors->GetColor3d("Black").GetData());
+  actor->GetCubeProperty()->SetColor(colors->GetColor3d("PeachPuff").GetData());
 
   // a renderer and render window
   vtkNew<vtkRenderer> renderer;
@@ -35,12 +70,22 @@ int main(int, char*[])
   vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
   renderWindowInteractor->SetRenderWindow(renderWindow);
 
-  // Create the widget and its representation
+  // create the widget and its representation
   vtkNew<vtkCompassRepresentation> compassRepresentation;
+#ifdef VTK_HAS_IMPROVED_COMPASSWIDGETREPRESENTATION
+  compassRepresentation->SetMinimumDistance(2);
+  compassRepresentation->SetMaximumDistance(10);
+#endif
 
   vtkNew<vtkCompassWidget> compassWidget;
   compassWidget->SetInteractor(renderWindowInteractor);
   compassWidget->SetRepresentation(compassRepresentation);
+  compassWidget->SetDistance(5.0);
+
+  // create the callback
+  vtkNew<vtkICWValueChangedCallback> valueChangedCallback;
+  compassWidget->AddObserver(vtkCommand::WidgetValueChangedEvent,
+                             valueChangedCallback);
 
   // add the actors to the scene
   renderer->AddActor(actor);
@@ -52,8 +97,11 @@ int main(int, char*[])
   renderWindow->Render();
   compassWidget->EnabledOn();
 
-  vtkNew<vtkInteractorStyleTrackballCamera> style;
-  renderWindowInteractor->SetInteractorStyle(style);
+  // no interactor style - camera is moved by widget callback
+  renderWindowInteractor->SetInteractorStyle(nullptr);
+
+  // set camera to initial position
+  compassWidget->InvokeEvent(vtkCommand::WidgetValueChangedEvent);
 
   // begin interaction
   renderWindowInteractor->Start();