Box2d 处理动态创建的实体

Question

我正在尝试学习 box2d，但我遇到了问题。我的项目中有 3 个实体，实际上是 3 行。我正在尝试将每条线的 y 坐标设置为 -7，当它们到达 y 坐标 14 时。我检查它们是否超过 14 的代码如下：

for (int i = 0; i < groundsArray.size(); i++) {

     Body body2 = groundsArray.get(i);

     float x_deg;
     x_deg = body2.getTransform().getPosition().x;

  if (body2.getUserData().equals("grounds" + i)   && body2.getTransform().getPosition().y > 14) {
     body2.setTransform(x_deg, -7, 0);

  }

}

我如何创建身体：

 public void createGrounds(int i) {

  // for some random positions
  int rnd = random.nextInt(10);
  int constant = -20;
  int new_y = i * 7;

  int result_x1 = constant + rnd;
  int result_x2 = result_x1 + 16;

  BodyDef bodyDef = new BodyDef();
  FixtureDef fixtureDef = new FixtureDef();

  // GROUND LEFT
  // body definition
  bodyDef.type = BodyType.StaticBody;
  bodyDef.position.set(0, 0);


  // ground shape
  ChainShape groundShape = new ChainShape();
  groundShape.createChain(new Vector2[] { new Vector2(result_x1, -new_y),new Vector2(result_x2, -new_y) });

  // fixture definition
  fixtureDef.shape = groundShape;
  fixtureDef.friction = 5f;
  fixtureDef.restitution = 0;

  grounds = world.createBody(bodyDef);
  grounds.createFixture(fixtureDef);

  grounds.setUserData("grounds" + i);
  groundsArray.add(grounds);

  groundShape.dispose();
}

我如何在 show() 中调用 createGrounds()：

for (int i = 0; i <= 2; i++) {
     createGrounds(i);

  }

我如何在 render() 中更新世界和位置：

  public void render(float delta) {
  Gdx.gl.glClearColor(0, 0, 0, 0);
  Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

  accelX = Gdx.input.getAccelerometerX();
  Vector2 gravity = new Vector2(-accelX * 6, -60.81f);
  world.setGravity(gravity);

  world.step(TIMESTEP, VELOCITYITERATIONS, POSITIONITERATIONS);

  batch.setProjectionMatrix(camera.combined);
  batch.begin();

  world.getBodies(tmpBodies);
  for (Body body : tmpBodies) {

     if (body.getUserData().equals(ballsprite)
           && body.getUserData() instanceof Sprite) {
        Sprite sprite = (Sprite) body.getUserData();
        sprite.setPosition(
              body.getPosition().x - sprite.getWidth() / 2,
              body.getPosition().y - sprite.getHeight() / 2);
        sprite.setRotation(body.getAngle() * MathUtils.radiansToDegrees);
        sprite.draw(batch);
     }

     float x_deg;
     float y_deg;

     x_deg = body.getTransform().getPosition().x;
     y_deg = body.getTransform().getPosition().y;
     y_deg = y_deg + game_speed;
     body.setTransform(x_deg, y_deg, 0);

  }

  // The part i couldn't solve
  for (int i = 0; i < groundsArray.size(); i++) {

     Body body2 = groundsArray.get(i);

     float x_deg;
     x_deg = body2.getTransform().getPosition().x;

     if (body2.getUserData().equals("grounds" + i)
           && body2.getTransform().getPosition().y > 14) {
        body2.setTransform(x_deg, -7, 0);

     }

  }

  batch.end();
  debugRenderer.render(world, camera.combined);

}

Answer 1

也许把你的 for 循环改成这个

for(int i = groundsArray.size(); i > 0; i--){}