Method Spin

Interaction/Style/vtkInteractorStyleTrackballActor.cxx:295–362

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//------------------------------------------------------------------------------
void vtkInteractorStyleTrackballActor::Spin()
{
  if (this->CurrentRenderer == nullptr || this->InteractionProp == nullptr)
  {
    return;
  }

  vtkRenderWindowInteractor* rwi = this->Interactor;
  vtkCamera* cam = this->CurrentRenderer->GetActiveCamera();

  // Get the axis to rotate around = vector from eye to origin

  double* obj_center = this->InteractionProp->GetCenter();

  double motion_vector[3];
  double view_point[3];

  if (cam->GetParallelProjection())
  {
    // If parallel projection, want to get the view plane normal...
    cam->ComputeViewPlaneNormal();
    cam->GetViewPlaneNormal(motion_vector);
  }
  else
  {
    // Perspective projection, get vector from eye to center of actor
    cam->GetPosition(view_point);
    motion_vector[0] = view_point[0] - obj_center[0];
    motion_vector[1] = view_point[1] - obj_center[1];
    motion_vector[2] = view_point[2] - obj_center[2];
    vtkMath::Normalize(motion_vector);
  }

  double disp_obj_center[3];

  this->ComputeWorldToDisplay(obj_center[0], obj_center[1], obj_center[2], disp_obj_center);

  double newAngle =
    vtkMath::DegreesFromRadians(atan2(rwi->GetEventPosition()[1] - disp_obj_center[1],
      rwi->GetEventPosition()[0] - disp_obj_center[0]));

  double oldAngle =
    vtkMath::DegreesFromRadians(atan2(rwi->GetLastEventPosition()[1] - disp_obj_center[1],
      rwi->GetLastEventPosition()[0] - disp_obj_center[0]));

  double scale[3];
  scale[0] = scale[1] = scale[2] = 1.0;

  double** rotate = new double*[1];
  rotate[0] = new double[4];

  rotate[0][0] = newAngle - oldAngle;
  rotate[0][1] = motion_vector[0];
  rotate[0][2] = motion_vector[1];
  rotate[0][3] = motion_vector[2];

  this->Prop3DTransform(this->InteractionProp, obj_center, 1, rotate, scale);