Box2d Fixed Timestep and Interpolation

Question

I am using libGDX and I have problems implementing the box2d fixed timestep with interpolation.

This is my code:

private void updateWorld() {

    accumulator += Gdx.graphics.getDeltaTime();

    while (accumulator>= step) { // The step is 1/10

        copyCurrentPosition();

        world.step(step, 8, 3);
        accumulator -= step;
    }

    interpolate(accumulator / step);
}

private void copyCurrentPosition() {
    prevPosition = new Vector2(player.body.getPosition().x, player.body.getPosition().y);
}

private void interpolate(float alpha) {
    player.body.setTransform(player.body.getPosition().x * alpha + prevPosition.x * (1.0f - alpha), player.body.getPosition().y * alpha + prevPosition.y * (1.0f - alpha), 0);
}

Answer 1

That's a pretty large time step (0.1s), which almost certainly spans multiple render frames. The LibGDX docs recommend either 1/45f or 1/300f for that argument. I've personally been using 1/300f and it works fine.

The docs also recommend 6 and 2 (vs your 8 and 3) for the other arguments, but these are close enough together it's probably not that critical.