[vtkusers] Why can we still instantiate vtkRenderWindow though it is abstract class?

[Jérôme]

Hi,
This is exactly why you use ::New( ) to instantiate instead of the
usual 'new' operator. VTK implements an object factory that will
choose for you the right concrete class derived from vtkRenderWindow.

See: vtkRenderWindow *vtkRenderWindow::New() in Rendering/vtkRenderWindow.cxx
and: vtkObject* vtkGraphicsFactory::CreateInstance(const char*
vtkclassname ) in Rendering/vtkGraphicsFactory.cxx

VTK's developpers may give some precisions if I missed something!

HTH
Jerome

2011/4/22 wayne5ning <wayne5ning at gmail.com>:
> Usually, we instantiate our window in the following way:
> vtkSmartPointer<vtkRenderWindow> renderWnd  = vtkRenderWindow::New();
>
> But when I look into the declaration of vtkRenderWindow, I find that it's an
> abstract class as it has pure abstract member functions like
> virtual void Start() = 0;
>
> So I'm confused because I've learned that abstract classes cannot be
> instantiated, but here the instantiation succeeds.
>
> Then when I examine the class reference of its subclass
> http://www.vtk.org/doc/nightly/html/classvtkOpenGLRenderWindow.html
> vtkOpenGLRenderWindow , I find this:
>
> vtkOpenGLRenderWindow is a concrete implementation of the abstract class
> vtkRenderWindow. vtkOpenGLRenderer interfaces to the OpenGL graphics
> library. Application programmers should normally use vtkRenderWindow instead
> of the OpenGL specific version.
>
> The suggestion "Application programmers should normally use vtkRenderWindow
> instead of the OpenGL specific version." makes me more confused.
>
>
>
>
> --
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