Andengine Fixtures, Gravity, Mass - permanent bouncing ball

Question

gravity: (x=0, y=EARTH)

I want make permanent bouncing ball. For example I set it coords (200, 200), after it falls down to ground, bounces and return to the same coords as in begin (200, 200). I tried to play with density, elasticity, friction and I got some similar behavior, but is changing. I google a lot and found that the problem is because of rounding floats. Question: which value is changing in engine and which I need to reset after that value will become more then some delta?

Second question: why if I set fixtures like this: fixtures(density=1, elasticity=1, friction=0) it not bounced to the same height, but bouncing with every bounce higher? I set elasticity something like 0,981f

Third question: how one object fixtures depends on second object fixtures? example: ball(1f, 0.6f, 1f) wall(1f, 0.6f, 0f)

and

ball(1f, 0.6f, 1f) wall(1f, 0.6f, 0.5f)

what will change?

Answer 1

hmmm, to make a permanent bouncing ball, Make your body BodyType.DynamicBody one, then just set the gravity to 0,EARTH (9.8f) and

scene.registerUpdateHandler(new IUpdateHandler() {


    @Override
    public void onUpdate(float pSecondsElapsed) {

            if(body.getPosition().y >=CAMERA_HEIGHT)
            {
                Vector2 v=new Vector2(0, -9f); //Adjust according to the bounce required
                body.setLinearVelocity(v);
            }

    }
});

The second one :

density is the volumetric mass density (),, and gravitational acceleration is independent of mass...

elasticity is the inertia when the object is stopped at a point, so if you don't want to move the body further just set it to 0

friction is the amount of the force resisting the relative motion of the body (like medium air, water or things like that)

So, to create a bouncing ball between two fixed points try setting (density=1, elasticity=0, friction=0)