When the parent of the quad is
viz.ORTHO you can specify the subwindow to add the quad to with the scene argument:
Code:
import viz
viz.go()
viz.addChild('gallery.osgb')
subWindow = viz.addWindow()
blackScreen = viz.addTexQuad(parent=viz.ORTHO,scene=subWindow,scale=[500]*3,color=viz.BLACK)
blackScreen.alpha(0.0)
vizact.onkeydown(' ',blackScreen.runAction,vizact.fadeTo(1.0,time=2.0))