[vtkusers] OpenGL Backbuffer on Mac

[Michael Rice]

The vtkRenderWindow::SwapBuffersOff() method turns off swapping the
backbuffer to the frontbuffer.

On Windows, the vtkWin32OpenGLRenderWindow::Frame() method checks this flag
and does not do the swap if it swapping is turned off. The same is true for
vtkXOpenGLRenderWindow::Frame().

However, on Mac, neither the vtkCarbonRenderWindow::Frame() or
vtkCocoaRenderWindow::Frame() methods check this flag before doing the swap.

Is there a reason for this?

Thanks.
Michael