viewport settings in stereo mode. It seems that the SceneView::cull()
method will pass the full size viewport to the left/right
cullvisitors, instead of the modified stereo viewport. I made quite a
few changes to SceneView to fix the issue. The SceneView::cullStage()
method will now receive the viewport as an argument, instead of using
the global viewport. The SceneView::cull() method will pass the
modifed viewport to cullStage when rendering in stereo.
There are 2 new private methods computeLeftEyeViewport() and
computeRightEyeViewport() that will compute the stereo viewports. I
also modified the draw() function so it applies the correct viewport
to the prerender stages. These changes are only necessary for
horizontal/vertical split stereo."