Java 使用Box2D应用Y线性脉冲时X速度减慢

我使用libgdx和box2d作为我的物理引擎。现在我有一个非常简单的盒子，在一个平面上进行控制：

一切似乎都很顺利。我用箭头键控制这个盒子。如果我按下向右箭头，盒子将向右加速。当我按下向上箭头时，盒子会跳起来但出乎意料的是，当盒子跳跃时，它的x速度减慢。有人能告诉我为什么会这样以及如何解决吗？

仅使用一些Box2d设置的播放器对象：

public class Player extends Entity {
  private static BodyDef createBodyDef() {
    BodyDef bodyDef = new BodyDef();
    bodyDef.type = BodyDef.BodyType.DynamicBody;
    bodyDef.fixedRotation = true;
    bodyDef.position.set(100, 200);
    return bodyDef;
  }

  public Player(World world) {
    super(world, createBodyDef(), Textures.rectangle(Units.m2P(0.7f), Units.m2P(2f), Color.RED));
    FixtureDef fixtureDef = new FixtureDef();
    PolygonShape shape = new PolygonShape();
    shape.setAsBox(50, 50, new Vector2(50, 50), 0f);
    fixtureDef.shape = shape;
    fixtureDef.friction = 0.1f;
    getBody().createFixture(fixtureDef);
    MassData massData = new MassData();
    massData.mass = 90f;
    getBody().setMassData(massData);
  }
}

public class GameScreen extends BaseScreen implements InputProcessor {
  private final World world = new World(new Vector2(0, -200), false);
  private final GameView view = new GameView();
  private final List<Entity> entities = new ArrayList<Entity>();
  private final Player player = new Player(world);
  private final List<Integer> pressedKeys = new ArrayList<Integer>();

  public GameScreen() {
    entities.add(player);
    view.setFollowEntity(player);
    MapBodyBuilder.buildShapes(view.getTiledMap(), 1, world);
  }

  @Override public void show() {
    super.show();
    Gdx.input.setInputProcessor(this);
  }

  @Override public void render(float delta) {
    super.render(delta);

    float forceX = 0f;
    float forceY = 0f;
    float force = 15000;
    if (pressedKeys.contains(Input.Keys.LEFT)) {
      forceX -= force;
    }
    if (pressedKeys.contains(Input.Keys.RIGHT)) {
      forceX += force;
    }
    if (pressedKeys.contains(Input.Keys.DOWN)) {
      forceY -= force;
    }

    player.getBody().applyForceToCenter(forceX, forceY, false);

    world.step(delta, 5, 5);
    view.render(entities);
  }

  @Override public void resize(int width, int height) {
    super.resize(width, height);
  }

  @Override public void hide() {
    super.hide();
    Gdx.input.setInputProcessor(null);
  }

  @Override public void dispose() {
    super.dispose();
    world.dispose();
    for (Entity entity : entities) {
      entity.dispose();
    }
  }

  @Override public boolean keyDown(int keycode) {
    if (keycode == Input.Keys.UP) {
      Body body = player.getBody();
      body.applyLinearImpulse(new Vector2(0, 30000), body.getWorldCenter(), true);
    }

    pressedKeys.add(keycode);
    return false;
  }

  @Override public boolean keyUp(int keycode) {
    pressedKeys.remove((Integer) keycode);
    return false;
  }

  @Override public boolean keyTyped(char character) {
    return false;
  }

  @Override public boolean touchDown(int screenX, int screenY, int pointer, int button) {
    return false;
  }

  @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) {
    return false;
  }

  @Override public boolean touchDragged(int screenX, int screenY, int pointer) {
    return false;
  }

  @Override public boolean mouseMoved(int screenX, int screenY) {
    return false;
  }

  @Override public boolean scrolled(int amount) {
    return false;
  }

  public Player getPlayer() {
    return player;
  }
}

游戏屏幕：

public class Player extends Entity {
  private static BodyDef createBodyDef() {
    BodyDef bodyDef = new BodyDef();
    bodyDef.type = BodyDef.BodyType.DynamicBody;
    bodyDef.fixedRotation = true;
    bodyDef.position.set(100, 200);
    return bodyDef;
  }

  public Player(World world) {
    super(world, createBodyDef(), Textures.rectangle(Units.m2P(0.7f), Units.m2P(2f), Color.RED));
    FixtureDef fixtureDef = new FixtureDef();
    PolygonShape shape = new PolygonShape();
    shape.setAsBox(50, 50, new Vector2(50, 50), 0f);
    fixtureDef.shape = shape;
    fixtureDef.friction = 0.1f;
    getBody().createFixture(fixtureDef);
    MassData massData = new MassData();
    massData.mass = 90f;
    getBody().setMassData(massData);
  }
}

public class GameScreen extends BaseScreen implements InputProcessor {
  private final World world = new World(new Vector2(0, -200), false);
  private final GameView view = new GameView();
  private final List<Entity> entities = new ArrayList<Entity>();
  private final Player player = new Player(world);
  private final List<Integer> pressedKeys = new ArrayList<Integer>();

  public GameScreen() {
    entities.add(player);
    view.setFollowEntity(player);
    MapBodyBuilder.buildShapes(view.getTiledMap(), 1, world);
  }

  @Override public void show() {
    super.show();
    Gdx.input.setInputProcessor(this);
  }

  @Override public void render(float delta) {
    super.render(delta);

    float forceX = 0f;
    float forceY = 0f;
    float force = 15000;
    if (pressedKeys.contains(Input.Keys.LEFT)) {
      forceX -= force;
    }
    if (pressedKeys.contains(Input.Keys.RIGHT)) {
      forceX += force;
    }
    if (pressedKeys.contains(Input.Keys.DOWN)) {
      forceY -= force;
    }

    player.getBody().applyForceToCenter(forceX, forceY, false);

    world.step(delta, 5, 5);
    view.render(entities);
  }

  @Override public void resize(int width, int height) {
    super.resize(width, height);
  }

  @Override public void hide() {
    super.hide();
    Gdx.input.setInputProcessor(null);
  }

  @Override public void dispose() {
    super.dispose();
    world.dispose();
    for (Entity entity : entities) {
      entity.dispose();
    }
  }

  @Override public boolean keyDown(int keycode) {
    if (keycode == Input.Keys.UP) {
      Body body = player.getBody();
      body.applyLinearImpulse(new Vector2(0, 30000), body.getWorldCenter(), true);
    }

    pressedKeys.add(keycode);
    return false;
  }

  @Override public boolean keyUp(int keycode) {
    pressedKeys.remove((Integer) keycode);
    return false;
  }

  @Override public boolean keyTyped(char character) {
    return false;
  }

  @Override public boolean touchDown(int screenX, int screenY, int pointer, int button) {
    return false;
  }

  @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) {
    return false;
  }

  @Override public boolean touchDragged(int screenX, int screenY, int pointer) {
    return false;
  }

  @Override public boolean mouseMoved(int screenX, int screenY) {
    return false;
  }

  @Override public boolean scrolled(int amount) {
    return false;
  }

  public Player getPlayer() {
    return player;
  }
}

公共类GameScreen扩展BaseScreen实现InputProcessor{
私有最终世界=新世界（新向量2（0，-200），假）；
私有最终GameView视图=新GameView（）；
私有最终列表实体=新的ArrayList（）；
私人决赛选手=新选手（世界）；
private final List pressedKeys=new ArrayList（）；
公共游戏屏幕（）{
实体。添加（玩家）；
view.setfollownity（播放器）；
MapBodyBuilder.buildShapes（view.getTiledMap（），1，world）；
}
@覆盖公共void show（）{
super.show（）；
Gdx.input.setInputProcessor（此）；
}
@替代公共无效渲染（浮动增量）{
超级渲染（delta）；
浮动力x=0f；
浮动力y=0f；
浮力=15000；
if（按Keys.contains（Input.Keys.LEFT））{
力-=力；
}
if（按Keys.contains（Input.Keys.RIGHT））{
力X+=力；
}
如果（按按键。包含（输入。按键。向下））{
力-=力；
}
player.getBody（）.applyForceToCenter（forceX，forceY，false）；
世界台阶（三角洲，5，5）；
视图。渲染（实体）；
}
@替代公共空心调整大小（整型宽度、整型高度）{
超级。调整大小（宽度、高度）；
}
@覆盖公共void hide（）{
super.hide（）；
Gdx.input.setInputProcessor（null）；
}
@重写公共void dispose（）{
super.dispose（）；
世界。处置（）；
for（实体：实体）{
entity.dispose（）；
}
}
@覆盖公共布尔键关闭（int-keycode）{
if（keycode==Input.Keys.UP）{
Body Body=player.getBody（）；
applylinearpulse（新向量2（0，30000），body.getWorldCenter（），true）；
}
按按键。添加（按键代码）；
返回false；
}
@重写公共布尔键控（int-keycode）{
按按键。删除（（整数）键码）；
返回false；
}
@重写公共布尔键类型（字符字符）{
返回false；
}
@覆盖公共布尔接地（int screenX、int screenY、int指针、int按钮）{
返回false；
}
@覆盖公共布尔补色（int screenX、int screenY、int指针、int按钮）{
返回false；
}
@重写公共布尔值（int-screenX、int-screenY、int-pointer）{
返回false；
}
@覆盖公共布尔mouseMoved（int-screenX，int-screenY）{
返回false；
}
@覆盖已滚动的公共布尔值（整数金额）{
返回false；
}
公共播放器getPlayer（）{
返回球员；
}
}

查看移动机构的工作原理：

计算力X和力Y（根据按下的键）

施力

当然，你不能用它来跳跃来避免“飞行”，所以你要用applyLinearImpulse（）来添加一次力（只需将其推到顶部），但棘手的是你要取消你在2中添加的力。-记住在Box2D中所有力都在世界上执行。步骤（…）所有计算后执行

而不是

    if (keycode == Input.Keys.UP) 
    {
        Body body = player.getBody();
        body.applyLinearImpulse(new Vector2(0, 30000), body.getWorldCenter(), true);
    }

做点像

    if (keycode == Input.Keys.UP) 
    {
        jumpForce = 30000; //jumpForce is variable of GameScreen class
    }

然后在渲染方法中

    ...

    if (pressedKeys.contains(Input.Keys.DOWN)) 
    {
        forceY -= force;
    }

    forceY += jumpForce; //here you add the jump force

    player.getBody().applyForceToCenter(forceX, forceY, false);

    jumpForce = 0; //but only once - in next iteration od render it will be avoided till UP key will be pressed again

当然，你可以考虑你自己的机制，但这是正确的方向