Java SE (Java Platform, Standard Edition)

Hi, all

I built some polyhedrons using IndexedTriangleArray, the normal for each
vertex point is (0.0, -1.0, 0.0). I used the following code to set the
appearance:

PolygonAttributes pa = new PolygonAttributes();
pa.setCullFace(PolygonAttributes.CULL_NONE);
pa.setBackFaceNormalFlip(true);

Appearance app = new Appearance();
app.setPolygonAttributes(pa);

I also applied the lights and MouseZoom to my TransformGroup object using
the following code:

//add AmbientLight and DirectionalLight to objScale
AmbientLight lightA = new AmbientLight(new Color3f(0.2f,0.2f,0.2f));
lightA.setInfluencingBounds(new BoundingSphere());
objScale.addChild(lightA);

DirectionalLight lightD1 = new DirectionalLight();
lightD1.setInfluencingBounds(new BoundingSphere());
Vector3f direction = new Vector3f(0.0f, -1.0f, 0.0f);
direction.normalize();
lightD1.setDirection(direction);
lightD1.setColor(new Color3f(0.0f, 1.0f, 0.0f));
objScale.addChild(lightD1);

MouseZoom behavior2 = new MouseZoom();
behavior2.setTransformGroup(objScale);
objScale.addChild(behavior2);
behavior2.setSchedulingBounds(bounds);

Now my trouble is, if I keep zooming in, I can not see some sides of the
polyhedrons. It seems that the normals changed. I do not have this trouble
if I keep zooming out. I am not sure if this is normal, lighting, or appearance
problem.

Any help will be highly appreciated.

Gaoming