相信很多做研究的人都在使用VTK，其实VTK的学习分成两类。一类就是使用VTK中现有的算法来完成自己的工作，比如数据的显示和渲染。另外一类是需要继承里面的算法类，自己根据自己的需求来重新写一个算法。
对于第一种类型的应用，不要觉得使用C++来写代码会很复杂，其实不复杂。此种应用一般都是从数据源出发，然后顺着数据流管线一路往下走，最后显示。是面向过程的。
图1 简单的VTK管线流
下面的一个例子，就是这样的一个简单的应用，使用了AppendFilter算法。
#include <vtkActor.h>
#include <vtkAppendFilter.h>
#include <vtkDataSetMapper.h>
#include <vtkGlyph3DMapper.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPointSource.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkProperty.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkUnstructuredGrid.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <iostream>vtkSmartPointer<vtkActor> Point2Glyph(vtkPoints* points,double const& scale);int main(int,char**)
{// Create 9 pointsvtkNew<vtkPointSource> pointSource;pointSource->SetNumberOfPoints(9);pointSource->Update();vtkSmartPointer<vtkPolyData> polydata=pointSource->GetOutput();std::cout<<"There are "<<polydata->GetNumberOfPoints()<<" points in the polydata set."<<std::endl;// Create 2 points in a vtkUnstructuredGridvtkNew<vtkPoints> points;points->InsertNextPoint(0,0,0);points->InsertNextPoint(0,0,1);vtkNew<vtkUnstructuredGrid> ug;ug->SetPoints(points);std::cout<<"There are "<<ug->GetNumberOfPoints()<<" points in the unstructured grid."<<std::endl;// Combine the two data setsvtkNew<vtkAppendFilter> appendFilter;appendFilter->AddInputData(polydata);appendFilter->AddInputData(ug);appendFilter->Update();vtkSmartPointer<vtkUnstructuredGrid> combined=appendFilter->GetOutput();std::cout<<"There are "<<combined->GetNumberOfPoints()<<" points combined."<<std::endl;// Create a mapper and actorvtkNew<vtkNamedColors> colors;vtkNew<vtkDataSetMapper> mapper;mapper->SetInputConnection(appendFilter->GetOutputPort());vtkNew<vtkActor> actor;actor->SetMapper(mapper);vtkSmartPointer<vtkActor> sphereActor=Point2Glyph(appendFilter->GetOutput()->GetPoints(),0.25);sphereActor->GetProperty()->SetColor(colors->GetColor3d("Gold").GetData());// Create renderer window and interactorvtkNew<vtkRenderer> ren;vtkNew<vtkRenderWindow> renWin;renWin->SetSize(1024,1024);renWin->AddRenderer(ren);vtkNew<vtkRenderWindowInteractor> iren;iren->SetRenderWindow(renWin);vtkNew<vtkInteractorStyleTrackballCamera> style;iren->SetInteractorStyle(style);ren->AddActor(actor);ren->AddActor(sphereActor);ren->SetBackground(colors->GetColor3d("RoyalBlue").GetData());iren->Initialize();iren->Start();return 0;
}vtkSmartPointer<vtkActor> Point2Glyph(vtkPoints* points,double const& scale){double* bounds=points->GetBounds();double maxLen=0;for(int i=1;i<3;++i){maxLen=std::max(bounds[i+1]-bounds[i],maxLen);}vtkNew<vtkSphereSource> sphereSource;sphereSource->SetRadius(scale*maxLen);sphereSource->SetThetaResolution(30);sphereSource->SetPhiResolution(30);vtkNew<vtkPolyData> pd;pd->SetPoints(points);vtkNew<vtkGlyph3DMapper> mapper;mapper->SetInputData(pd);mapper->SetSourceConnection(sphereSource->GetOutputPort());mapper->ScalarVisibilityOff();mapper->ScalingOff();vtkNew<vtkActor> actor;actor->SetMapper(mapper);return actor;
}
输出的结果如下：
图2 输出结果