VTK Visualizer in a C++ Class Does not Render the Scene - c++

Question

I am trying to put the example provided by VTK here into a C++ class. This example reads an STL file and visualizes it in a window.
Below is my code for which I get no compiler or run-time error. My input STL file is read correctly but my code exits without producing any visualization of the STL object.
In my C++ class, I organized the VTK example code by separating the reader from the visualizer and putting them into two functions in the class. The visualizer uses a mapper, actor, and a renderer to visualize the STL object. However, I am not able to get the code to visualize my STL object.
The only way I am able to get my C++ class to work is to copy the codes of the function visualize into my readSTL function, then I can see the window with my STL object rendered in it.
Could someone kindly give me some hints how I can perform the visualization in a separate function in the class?
#include <vtkPolyData.h>
#include <vtkSTLReader.h>
#include <vtkSmartPointer.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
class triangulation
{
public:
vtkIdType numberOfFaces;
// Constructor
triangulation(void);
triangulation(std::string filename);
void setFilename(std::string filename);
std::string getFilename(void);
// Getters
vtkSmartPointer<vtkPolyData> getMesh(void);
vtkSmartPointer<vtkCellArray> getPolys(void);
vtkSmartPointer<vtkPoints> getPoints(void);
vtkSmartPointer<vtkDataArray> getDataArray(void);
vtkIdType getNumberofFaces(void);
// Visualizer
void visualize(void);
// Reader
void readSTL(void);
private:
std::string stlFilename;
vtkSmartPointer<vtkPolyData> mesh;
vtkSmartPointer<vtkSTLReader> reader;
vtkSmartPointer<vtkCellArray> polys;
vtkSmartPointer<vtkPoints> points;
vtkSmartPointer<vtkDataArray> dataArray;
};
triangulation::triangulation()
{
//
}
triangulation::triangulation(std::string filename)
{
setFilename(filename);
}
void triangulation::readSTL(void)
{
vtkSmartPointer<vtkSTLReader> reader = vtkSmartPointer<vtkSTLReader>::New();
reader->SetFileName(stlFilename.c_str());
reader->Update();
mesh = reader->GetOutput();
polys = mesh->GetPolys();
points = mesh->GetPoints();
numberOfFaces = mesh->GetNumberOfCells();
}
void triangulation::setFilename(std::string filename)
{
stlFilename = filename;
}
std::string triangulation::getFilename(void)
{
return stlFilename;
}
vtkSmartPointer<vtkPolyData> triangulation::getMesh(void)
{
return mesh;
}
vtkSmartPointer<vtkCellArray> triangulation::getPolys(void)
{
return polys;
}
vtkIdType triangulation::getNumberofFaces(void)
{
return numberOfFaces;
}
vtkSmartPointer<vtkPoints> triangulation::getPoints(void)
{
return points;
}
vtkSmartPointer<vtkDataArray> triangulation::getDataArray(void)
{
return dataArray;
}
void triangulation::visualize(void)
{
// Visualize
vtkSmartPointer<vtkPolyDataMapper> mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
mapper->SetInputConnection(reader->GetOutputPort());
vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->AddRenderer(renderer);
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow(renderWindow);
renderer->AddActor(actor);
renderer->SetBackground(.3, .6, .3); // Background color green
renderWindow->Render();
renderWindowInteractor->Start();
}
int main(int argc, char *argv[])
{
if (argc != 2)
{
cout << "Required parameters: Filename" << endl;
return EXIT_FAILURE;
}
std::string inputFilename = argv[1];
cout << inputFilename << endl;
triangulation *tr = new triangulation(inputFilename);
tr->readSTL();
cout << "Number of Faces = " << tr->getNumberofFaces() << endl;
vtkSmartPointer<vtkPolyData> mesh = tr->getMesh();
vtkSmartPointer<vtkCellArray> polys = tr->getPolys();
vtkSmartPointer<vtkPoints> points = tr->getPoints();
vtkSmartPointer<vtkDataArray> data = tr->getDataArray();
//mesh->Print(cout);
// polys->Print(cout);
// points->Print(cout);
// data->Print(cout);
tr->visualize();
delete tr;
return EXIT_SUCCESS;
}
Here is my STL object that I used to test my code:
"myobject.stl":
solid STL generated by MeshLab
facet normal -4.919344e-01 2.986337e-01 8.178133e-01
outer loop
vertex -1.265660e+00 4.756133e+00 1.702858e-01
vertex -1.649185e+00 4.810246e+00 -8.017353e-02
vertex -1.602208e+00 4.484959e+00 6.686619e-02
endloop
endfacet
facet normal -5.898571e-01 2.603427e-01 7.643889e-01
outer loop
vertex -1.861084e+00 4.821712e+00 -2.475956e-01
vertex -1.602208e+00 4.484959e+00 6.686619e-02
vertex -1.649185e+00 4.810246e+00 -8.017353e-02
endloop
endfacet
facet normal -6.398674e-01 2.007942e-01 7.417893e-01
outer loop
vertex -1.861084e+00 4.821712e+00 -2.475956e-01
vertex -1.845646e+00 4.479523e+00 -1.416520e-01
vertex -1.602208e+00 4.484959e+00 6.686619e-02
endloop
endfacet
facet normal -6.901410e-01 1.854371e-01 6.995131e-01
outer loop
vertex -2.043903e+00 4.838252e+00 -4.323493e-01
vertex -1.845646e+00 4.479523e+00 -1.416520e-01
vertex -1.861084e+00 4.821712e+00 -2.475956e-01
endloop
endfacet
endsolid vcg

Answer 1

Your code will work if you simply replace the following line in triangulation::readSTL():
// Problem: local variable 'reader' shadows class member 'reader'.
vtkSmartPointer<vtkSTLReader> reader = vtkSmartPointer<vtkSTLReader>::New();
// Solution:
reader = vtkSmartPointer<vtkSTLReader>::New();
Because the class-member reader remains unintialized, the application crashes with a segfault when it is being accessed in triangulation::visualize().
Hint: you probably would not have encountered this problem if you consequently used this-> or a naming prefix (m_ or _) to refer to class members. See this SO post for some explanations.