NPR Line Rendering

The concept is rather simple, create clones of objects, turn that clones into a wire frame setting the color and the line widths and switch their culling so that they are drawn backface.

The code for doing this is like this...

public void outline(float width, Node node){
    if(node instanceof Shape3D){
        Shape3D shape = (Shape3D)node;
        Appearance app = shape.getAppearance();
        PolygonAttributes polyAtt =
            new PolygonAttributes(PolygonAttributes.POLYGON_LINE,
                                  PolygonAttributes.CULL_FRONT,
                                  0.0f);
        app.setPolygonAttributes(polyAtt);
        LineAttributes lineAtt =
            new LineAttributes(width,LineAttributes.PATTERN_SOLID,false);
        app.setLineAttributes(lineAtt);
        app.setTexture(null);
        app.setMaterial(null);
        ColoringAttributes colorAtt =
            new ColoringAttributes(0.0f,0.0f,0.0f,
                                   ColoringAttributes.FASTEST);
        app.setColoringAttributes(colorAtt);
        shape.setAppearance(app);
    }else if(node instanceof Morph){
        Morph shape = (Morph)node;
        Appearance app = shape.getAppearance();
        PolygonAttributes polyAtt =
            new PolygonAttributes(PolygonAttributes.POLYGON_LINE,
                                  PolygonAttributes.CULL_FRONT,
                                  0.0f);
        app.setPolygonAttributes(polyAtt);
        LineAttributes lineAtt =
            new LineAttributes(width,LineAttributes.PATTERN_SOLID,false);
        app.setLineAttributes(lineAtt);
        app.setTexture(null);
        app.setMaterial(null);
        ColoringAttributes colorAtt =
            new ColoringAttributes(0.0f,0.0f,0.0f,ColoringAttributes.FASTEST);
        app.setColoringAttributes(colorAtt);
        shape.setAppearance(app);
    }else if(node instanceof Group){
        Group group = (Group)node;
        int numChildren = group.numChildren();
        for(int i=0;i<numChildren;i++){
            outline(width, group.getChild(i));
        }
    }
}

  Node clone = bg.cloneTree(true);
  outline(8.0f, clone);
  bg.addChild(clone);

There may be additional things that can be done to this, like instead of cloning the entire scene, it would probably be better to clone only shape3ds and morphs, and attach them to the parent branch groups. And maybe even better instead of out right cloning shape3ds and morphs, to actual convert their geometry over manually and leave out any texture data (save some memory). I should also probably add color as another parameter to the function because black may not be the only color.

Leyland has provided a collection of screen shots showing the effects.

Shot 1 (before)

Shot 2 (after)

Shot 3 (another one)