This will result in GetSize() returning values different from X and Y in SetSize(X, Y) called prior.
Most often than not, if you try calling SetSize() multiple times with the same values it will end up
working even though it might not have worked the first time.
In a case where the WindowSize is not set to a size (X, Y) we wanted it to be set, the opengl framebuffer might be set to (X, Y) while the window RECT will have an (A, B) size. Doing GetSize()
on the vtkRenderer and the vtkRenderWindow will both return the size of the RECT. vtkRenderer::Getsize will not return (X, Y) even though this is this is the actual size of the render.
This seems to be mostly due to the fact that vtkRenderer::GetSize() and vtkRenderWindow::GetSize() both interrogate windowsize. If internal set SetSize() for vtkRenderer is correct vtkRenderer::GetSize() should interrogate something closer to the framebuffer size.