private void cleanupViewer(Viewer v) {
// Get view associated with this SimpleUniverse
View view = v.getView();
// cleanup all off-screen canvases
for (int i = view.numCanvas3Ds() - 1; i >= 0; i--) {
Canvas3D c = view.getCanvas3D(i);
if (c.isOffScreen()) {
c.setOffScreenBuffer(null);
}
}