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。