How do you make shading work between several 3D objects using rajawali?

Question

I made a 3D environment with a few 3D objects using rajawali. I set up a directionnal light, everything displays, I added diffuse material to every object.

But I can not have the shadow of one object on another.

The objects have their own shadows on themselves depending on how they are oriented within the directionnal light but they doesnt seem to have shadows of other objects. I also tried with a spotlight but it didnt work.

What can I do ? Is there a feature to enable or something ?

Here is my code :

public class BasicRenderer extends Renderer {
private Sphere mEarthSphere;
private DirectionalLight mDirectionalLight;
private SpotLight mSpotLight;
private Object3D[][][] mCubes;
private Object3D mRootCube;

public BasicRenderer(Context context) {
    super(context);

    setFrameRate(60);
}


@Override
protected void initScene() {
    getCurrentScene().setBackgroundColor(0, 0.5f, 1.0f, 1.0f);
    getCurrentScene().setFog(new FogMaterialPlugin.FogParams(FogMaterialPlugin.FogType.LINEAR, 0x999999, 50, 100));

    mSpotLight = new SpotLight();
    mSpotLight.setPower(20);
    mSpotLight.enableLookAt();
    mSpotLight.setPosition(new Vector3(2, 1, 0));
    mSpotLight.setLookAt(0,0,0);
    //getCurrentScene().addLight(mSpotLight);

    mDirectionalLight = new DirectionalLight(-1f, -2f, -1.0f);
    mDirectionalLight.setColor(1.0f, 1.0f, 1.0f);
    mDirectionalLight.setPower(1.5f);
    getCurrentScene().addLight(mDirectionalLight);


    SpecularMethod.Phong phongMethod = new SpecularMethod.Phong(0xeeeeee, 200);

    Material material = new Material();
    material.enableLighting(true);
    material.setDiffuseMethod(new DiffuseMethod.Lambert());
    //material.setSpecularMethod(phongMethod);
    Texture earthTexture = new Texture("Earth", R.drawable.earthtruecolor_nasa_big);
    NormalMapTexture earthNormal = new NormalMapTexture("earthNormal", R.drawable.earthtruecolor_nasa_big_n);
    earthTexture.setInfluence(.5f);
    try{
        material.addTexture(earthTexture);
        material.addTexture(earthNormal);

    } catch (ATexture.TextureException error){
        Log.d("BasicRenderer" + ".initScene", error.toString());
    }
    material.setColorInfluence(0);
    mEarthSphere = new Sphere(1, 24, 24);
    mEarthSphere.setMaterial(material);
    getCurrentScene().addChild(mEarthSphere);
    getCurrentCamera().setZ(4.2f);

    mCubes = new Object3D[30][30][2];

    Material cubeMaterial = new Material();
    cubeMaterial.enableLighting(true);
    cubeMaterial.setDiffuseMethod(new DiffuseMethod.Lambert(1));
    //cubeMaterial.setSpecularMethod(phongMethod);
    cubeMaterial.enableTime(true);
    cubeMaterial.setColorInfluence(0);
    Texture cubeTexture = new Texture("Stone", R.drawable.stone);
    try{
        cubeMaterial.addTexture(cubeTexture);

    } catch (ATexture.TextureException error){
        Log.d("BasicRenderer" + ".initScene", error.toString());
    }

    cubeMaterial.addPlugin(new DepthMaterialPlugin());
    mRootCube = new Cube(1);
    mRootCube.setMaterial(cubeMaterial);
    mRootCube.setY(-1f);
    // -- similar objects with the same material, optimize
    mRootCube.setRenderChildrenAsBatch(true);
    getCurrentScene().addChild(mRootCube);
    mCubes[0][0][0] = mRootCube;

    for(int z = 0; z < 2; z++) {
        for(int y = 0; y < 5; y++) {
            for (int x = 0; x < 30; x++) {
                Object3D cube = mRootCube.clone(true);
                cube.setY(-5 + y);
                cube.setX(-15 + x);
                cube.setZ(z);
                mRootCube.addChild(cube);
                mCubes[x][y][z] = cube;

            }
        }
    }
    Object3D cube = mRootCube.clone(true);
    cube.setY(0);
    cube.setX(-15 + 10);
    cube.setZ(1);
    mRootCube.addChild(cube);
    mCubes[5][10][1] = cube;
    getCurrentScene().addChild(mCubes[5][10][1]);


    // -- create a chase camera
    //    the first parameter is the camera offset
    //    the second parameter is the interpolation factor
    ChaseCamera chaseCamera = new ChaseCamera(new Vector3(0, 3, 16), mEarthSphere);
    // -- tell the camera which object to chase
    // -- set the far plane to 1000 so that we actually see the sky sphere
    chaseCamera.setFarPlane(1000);
    getCurrentScene().replaceAndSwitchCamera(chaseCamera, 0); //<--Also the only change!!!

}

@Override
public void onRender(final long elapsedTime, final double deltaTime) {
    super.onRender(elapsedTime, deltaTime);
    mEarthSphere.rotate(Vector3.Axis.Y, 1.0);
}

}

As you can see on the next picture, there is no shadow on the ground next to the cube on the left, but I think there should be.

https://i.stack.imgur.com/Sow6c.jpg