VTK_Learning_交互与拾取_单位拾取

1.单位拾取

示例代码：

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL)
VTK_MODULE_INIT(vtkInteractionStyle)
VTK_MODULE_INIT(vtkRenderingFreeType)
 
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkProperty.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
 
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkDataSetMapper.h>
#include <vtkCellPicker.h>
#include <vtkSelectionNode.h>
#include <vtkSelection.h>
#include <vtkRendererCollection.h>
#include <vtkExtractSelection.h>
#include <vtkObjectFactory.h>
 
/**************************************************************************/
class CellPickerInteractorStyle :public vtkInteractorStyleTrackballCamera
{
public:
  static CellPickerInteractorStyle* New();
 
  CellPickerInteractorStyle()
  {
    selectedMapper = vtkSmartPointer<vtkDataSetMapper>::New();
    selectedActor = vtkSmartPointer<vtkActor>::New();
  }
  virtual void OnLeftButtonDown()
  {
    int* pos = this->GetInteractor()->GetEventPosition();
    vtkSmartPointer<vtkCellPicker> picker =
      vtkSmartPointer<vtkCellPicker>::New();
    picker->SetTolerance(0.0005);
    picker->Pick(pos[0], pos[1], 0, this->GetDefaultRenderer());
 
    if (picker->GetCellId() != -1)
    {
      vtkSmartPointer<vtkIdTypeArray> ids =
        vtkSmartPointer<vtkIdTypeArray>::New();
      ids->SetNumberOfComponents(1);
      ids->InsertNextValue(picker->GetCellId());
 
      vtkSmartPointer<vtkSelectionNode> selectionNode =
        vtkSmartPointer<vtkSelectionNode>::New();
      selectionNode->SetFieldType(vtkSelectionNode::CELL);
      selectionNode->SetContentType(vtkSelectionNode::INDICES);
      selectionNode->SetSelectionList(ids);
 
      vtkSmartPointer<vtkSelection> selection =
        vtkSmartPointer<vtkSelection>::New();
      selection->AddNode(selectionNode);
 
      vtkSmartPointer<vtkExtractSelection> extractSelection =
        vtkSmartPointer<vtkExtractSelection>::New();
      extractSelection->SetInputData(0, polyData);
      extractSelection->SetInputData(1, selection);
      extractSelection->Update();
 
      selectedMapper->SetInputData((vtkDataSet*)extractSelection->GetOutput());
      selectedActor->SetMapper(selectedMapper);
      selectedActor->GetProperty()->EdgeVisibilityOn();
      selectedActor->GetProperty()->SetEdgeColor(1, 0, 0);
      selectedActor->GetProperty()->SetLineWidth(3);
 
      this->Interactor->GetRenderWindow()->GetRenderers()->GetFirstRenderer()->AddActor(selectedActor);
    }
    vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
  }
private:
  vtkSmartPointer<vtkPolyData>      polyData;
  vtkSmartPointer<vtkDataSetMapper> selectedMapper;
  vtkSmartPointer<vtkActor>         selectedActor;
};
/*********************************************************************************/
 
vtkStandardNewMacro(CellPickerInteractorStyle);
 
int main()
{
  vtkSmartPointer<vtkSphereSource> sphereSource =
    vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->Update();
 
  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputData(sphereSource->GetOutput());
 
  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  actor->GetProperty()->SetColor(0, 1, 0);
  actor->SetMapper(mapper);
 
  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  renderer->AddActor(actor);
  renderer->SetBackground(1, 1, 1);
 
  vtkSmartPointer<vtkRenderWindow> rw =
    vtkSmartPointer<vtkRenderWindow>::New();
  rw->Render();
  rw->SetWindowName("CellPicker Interaction");
  rw->AddRenderer(renderer);
 
  vtkSmartPointer<vtkRenderWindowInteractor> rwi =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  rwi->SetRenderWindow(rw);
/****************************************************************************/
  vtkSmartPointer<CellPickerInteractorStyle> style =
    vtkSmartPointer<CellPickerInteractorStyle>::New();
  style->SetDefaultRenderer(renderer);
  //style->polyData = sphereSource->GetOutput();
  rwi->SetInteractorStyle(style);
 
  rw->Render();
  rwi->Initialize();
  rwi->Start();
  return 0;
}

输出结果如下：

CellPickerInteractorStyle类同样派生自vtkInteraTrackballCamera，并通过重载该函数类的OnLeftButtonDown()函数来处理鼠标左键消息。PolyData为被拾取的模型数据，需要通过外部设置。在响应鼠标左键消息时，首先定义vtkCellPicker对象，使用Pick()函数实现拾取功能。拾取完毕，即可通过GetCellId()函数来得到当前拾取的单元索取号。
为了更方便地显示拾取的结果，可实现单元边的高亮显示。这里就涉及了vtkPolyData的局部数据提取功能。实现该功能时使用了几个新的类。

• vtkIdTypeArray:对象存储当前选中的单位的索引号，每次只选取一个单元，因此每次该对象仅有一个索引号；
• vtkSelectedNode对象与vtkSelection对象通常搭配使用，vtkSelection实际上是一个vtkSelectionNode的数组，而vtkSelectionNode则声明了要提取的数据的类型，这里SetFiledType()设置数据的类型为单元，SeiContentType()设置数据的内容为索引号。
• vtkExtractSelection:实现了数据提取功能，其第一个输入为被提取的vtkPolyData，第二个输入为vtkSelection对象，标记要提取的数据类型。

提取完毕，即可将提取的结果保存至一个vtkActor对象，并添加至当前的vtkRenderer中显示。