The pipelineexecute pipeline execution process of VTK learning

1. practice

#include <vtkSmartPointer.h>
#include <vtkBMPReader.h>
#include <vtkImageData.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkImageViewer2.h>
#include <vtkRenderWindow.h>

// The test file ：data/VTK-logo.bmp
int main(int argc, char* argv[])
{
	const char* str = "D:\\workshop\\VTK\\VTK\\vtk_source\\Examples\\Examples\\Chap02\\data\\VTK-logo.bmp";
	vtkSmartPointer<vtkBMPReader> reader = vtkSmartPointer<vtkBMPReader>::New();
	std::cout<<"Modification Time of reader (After New()): "<<reader->GetMTime()<<std::endl;
	reader->SetFileName(str);
	std::cout<<"Modification Time of reader (After SetFileName()): "<<reader->GetMTime()<<std::endl;
	
	vtkImageData* imageData = reader->GetOutput();
	std::cout<<"Modification Time of reader (After GetOutput()): "<<reader->GetMTime()<<std::endl;
	//reader->Update();
	std::cout<<"Modification Time of reader (After Update()): "<<reader->GetMTime()<<std::endl;

	int extent[6];
	imageData->GetExtent(extent);
	std::cout<<"Extent of image: "<<extent[0]<<" "
		<<extent[1]<<" "<<extent[2]<<" "<<extent[3]<<" "
		<<extent[4]<<" "<<extent[5]<<" "<<std::endl;

	vtkSmartPointer<vtkImageViewer2> viewer = 
		vtkSmartPointer<vtkImageViewer2>::New();
	vtkSmartPointer<vtkRenderWindowInteractor> interactor = 
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	viewer->SetupInteractor(interactor);
	viewer->SetInputData(imageData);
	viewer->Render();

	viewer->SetSize(640, 480);
	viewer->GetRenderWindow()->SetWindowName("vtkPipelineExecute");

	interactor->Initialize();
	interactor->Start();

	return EXIT_SUCCESS;
}

• no reader->Update()
  
• the reader->Update()
• 

2. principle