happy new year!
  here is the question .  I have many text boards to show. 
  1 which is better way to save memory , create a Object3D for each text  or create only one Object3D for all of text?
  2 if i created only one Object3D , how to hide part of this Object3D ? I have tried  get polygon id and using setVertexAlpha(polygonid, alpha) to archive this effect. it seems not work verywell,
    only first of call is work.  (this problem only on android )

  I use setCameraTo() to make world2 share world1's camera. yes it works .  Is it right?

Sorry my english is not good enough to describe what I want.

Could you tell me more details about how to share a camera between two worlds ?
Or  how to define a rendering order ?

thanks

I want to hide the PollyLine that on the top of the circle object.

So I can't use a transparent object.  right?
So I can't use texture with alpha channel. Because  I found the Object3D must be transparent mode otherwise the apha channel will not work.

Docments  saids : "Pollyline will be rendered after all objects have been drawn."
and It is true . see attachment, some lines is on the top of the circle. The circle object has been set to be transparent.

But if I disable the transparent of the circle. The PollyLine will not on top of the circle.  Is it by design?
How can I avoid this situation.

thanks for any comments.

I turn down the ambiant light of the world, and setup a light (seems a  spot light).
here are the code:

world.setAmbientLight(1, 1, 1);

Light light = new Light(world);
light.setIntensity(128, 128, 128);
light.setAttenuation(800);
light.setPosition(new SimpleVector(-100, 0, 100));

obj.setAdditionalColor(Color.blue);
world.addObject(obj);

is better ,but the sharp edges still not show up.

if i set up an ambient light, the scene looks like this:  the surface of the cube all are brightness , see attachment bad.png
i want it looks like good.png , but i can't find direct light to implement that effect.

help me out pls