Is it possible to add several Canvases (aka SimpleCanvasImpl classes)
to a JFrame?
Canvas3D canvas3D_1 = new Canvas3D("dog.x3d"); // Canvas3D extends SimpleCanvasImpl
Canvas3D canvas3D_2 = new Canvas3D("cat.x3d");
jframe.getContentPane().add(canvas3D_1); // that works
jframe.getContentPane().add(canvas3D_2); // now it doesn't work any more