VTK interactor style

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本文详细介绍了VTK（Visualization Toolkit）中的交互风格类vtkInteractorStyle的多种操作，包括开始和结束的动画、旋转、缩放、平移、旋转、焦距调整等。同时，深入解析了vtkInteractorStyleTrackballCamera类中实现旋转、平移和焦距变化的具体算法，涉及相机视角的调整、视点移动和光照更新。这些内容对于理解和使用VTK进行三维可视化交互具有重要意义。

占坑

	//vtkInteractorStyle
  virtual void StartAnimate();
  virtual void StopAnimate();
  virtual void StartRotate();
  virtual void EndRotate();
  virtual void StartZoom();
  virtual void EndZoom();
  virtual void StartPan();
  virtual void EndPan();
  virtual void StartSpin();
  virtual void EndSpin();
  virtual void StartDolly();
  virtual void EndDolly();
  virtual void StartUniformScale();
  virtual void EndUniformScale();
  virtual void StartTimer();
  virtual void EndTimer();
  virtual void StartTwoPointer();
  virtual void EndTwoPointer();

	//vtkInteractorStyleTrackballCamera.h
  void Rotate() override;
  void Spin() override;
  void Pan() override;
  void Dolly() override;

//vtkInteractorStyleTrackballCamera.cpp
//----------------------------------------------------------------------------
void vtkInteractorStyleTrackballCamera::Rotate()
{
  if (this->CurrentRenderer == nullptr)
  {
    return;
  }

  vtkRenderWindowInteractor *rwi = this->Interactor;

  int dx = rwi->GetEventPosition()[0] - rwi->GetLastEventPosition()[0];
  int dy = rwi->GetEventPosition()[1] - rwi->GetLastEventPosition()[1];

  int *size = this->CurrentRenderer->GetRenderWindow()->GetSize();

  double delta_elevation = -20.0 / size[1];
  double delta_azimuth = -20.0 / size[0];

  double rxf = dx * delta_azimuth * this->MotionFactor;
  double ryf = dy * delta_elevation * this->MotionFactor;

  vtkCamera *camera = this->CurrentRenderer->GetActiveCamera();
  camera->Azimuth(rxf);
  camera->Elevation(ryf);
  camera->OrthogonalizeViewUp();

  if (this->AutoAdjustCameraClippingRange)
  {
    this->CurrentRenderer->ResetCameraClippingRange();
  }

  if (rwi->GetLightFollowCamera())
  {
    this->CurrentRenderer->UpdateLightsGeometryToFollowCamera();
  }

  rwi->Render();
}

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

  vtkRenderWindowInteractor *rwi = this->Interactor;

  double *center = this->CurrentRenderer->GetCenter();

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

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

  vtkCamera *camera = this->CurrentRenderer->GetActiveCamera();
  camera->Roll( newAngle - oldAngle );
  camera->OrthogonalizeViewUp();

  rwi->Render();
}

//----------------------------------------------------------------------------
void vtkInteractorStyleTrackballCamera::Pan()
{
  if (this->CurrentRenderer == nullptr)
  {
    return;
  }

  vtkRenderWindowInteractor *rwi = this->Interactor;

  double viewFocus[4], focalDepth, viewPoint[3];
  double newPickPoint[4], oldPickPoint[4], motionVector[3];

  // Calculate the focal depth since we'll be using it a lot

  vtkCamera *camera = this->CurrentRenderer->GetActiveCamera();
  camera->GetFocalPoint(viewFocus);
  this->ComputeWorldToDisplay(viewFocus[0], viewFocus[1], viewFocus[2],
                              viewFocus);
  focalDepth = viewFocus[2];

  this->ComputeDisplayToWorld(rwi->GetEventPosition()[0],
                              rwi->GetEventPosition()[1],
                              focalDepth,
                              newPickPoint);

  // Has to recalc old mouse point since the viewport has moved,
  // so can't move it outside the loop

  this->ComputeDisplayToWorld(rwi->GetLastEventPosition()[0],
                              rwi->GetLastEventPosition()[1],
                              focalDepth,
                              oldPickPoint);

  // Camera motion is reversed

  motionVector[0] = oldPickPoint[0] - newPickPoint[0];
  motionVector[1] = oldPickPoint[1] - newPickPoint[1];
  motionVector[2] = oldPickPoint[2] - newPickPoint[2];

  camera->GetFocalPoint(viewFocus);
  camera->GetPosition(viewPoint);
  camera->SetFocalPoint(motionVector[0] + viewFocus[0],
                        motionVector[1] + viewFocus[1],
                        motionVector[2] + viewFocus[2]);

  camera->SetPosition(motionVector[0] + viewPoint[0],
                      motionVector[1] + viewPoint[1],
                      motionVector[2] + viewPoint[2]);

  if (rwi->GetLightFollowCamera())
  {
    this->CurrentRenderer->UpdateLightsGeometryToFollowCamera();
  }

  rwi->Render();
}

//----------------------------------------------------------------------------
void vtkInteractorStyleTrackballCamera::Dolly()
{
  if (this->CurrentRenderer == nullptr)
  {
    return;
  }

  vtkRenderWindowInteractor *rwi = this->Interactor;
  double *center = this->CurrentRenderer->GetCenter();
  int dy = rwi->GetEventPosition()[1] - rwi->GetLastEventPosition()[1];
  double dyf = this->MotionFactor * dy / center[1];
  this->Dolly(pow(1.1, dyf));
}

//----------------------------------------------------------------------------
void vtkInteractorStyleTrackballCamera::Dolly(double factor)
{
  if (this->CurrentRenderer == nullptr)
  {
    return;
  }

  vtkCamera *camera = this->CurrentRenderer->GetActiveCamera();
  if (camera->GetParallelProjection())
  {
    camera->SetParallelScale(camera->GetParallelScale() / factor);
  }
  else
  {
    camera->Dolly(factor);
    if (this->AutoAdjustCameraClippingRange)
    {
      this->CurrentRenderer->ResetCameraClippingRange();
    }
  }

  if (this->Interactor->GetLightFollowCamera())
  {
    this->CurrentRenderer->UpdateLightsGeometryToFollowCamera();
  }

  this->Interactor->Render();
}