在我看来这很奇怪。我基于fixturedef创建装置。我使用box2d的libgdx版本。这是我的密码：

System.out.println("category bits of fixtureDef: " + fixtureDef.filter.categoryBits);
System.out.println("mask bits of fixtureDef: " + fixtureDef.filter.maskBits);
System.out.println("category bits of fixtureDef: " + fixtureDef_leftPropeller.filter.categoryBits);
System.out.println("mask bits of fixtureDef: " + fixtureDef_leftPropeller.filter.maskBits);
System.out.println("category bits of fixtureDef: " + fixtureDef_rightPropeller.filter.categoryBits);
System.out.println("mask bits of fixtureDef: " + fixtureDef_rightPropeller.filter.maskBits);

Body body = world.createBody(Res.bodyDef_dynamic);
fixture = body.createFixture(fixtureDef);
fixture_leftPropeller = body.createFixture(fixtureDef_leftPropeller);
fixture_rightPropeller = body.createFixture(fixtureDef_rightPropeller);
body.setTransform(pos.x * Drone2D.MPP, pos.y * Drone2D.MPP, 0);
body.setUserData(drone);

System.out.println(" ");

for (Fixture fix : body.getFixtureList()) {
    System.out.println("category bits of fixture: " + fix.getFilterData().categoryBits);
    System.out.println("mask bits of fixture: " + fix.getFilterData().maskBits);
}

此代码的输出为：

category bits of fixtureDef: 2
mask bits of fixtureDef: 11
category bits of fixtureDef: 2
mask bits of fixtureDef: 11
category bits of fixtureDef: 2
mask bits of fixtureDef: 11

category bits of fixture: 4
mask bits of fixture: -1
category bits of fixture: 4
mask bits of fixture: -1
category bits of fixture: 4
mask bits of fixture: -1

什么？我的fixture的过滤位怎么可能与它们创建时使用的fixturedef不同呢？
我也发现了这一点：这些装置得到的面具是我在创建这些新装置之前销毁的身体面具。
不过，这不应该发生。
有人知道什么会导致这种行为吗？
编辑：
我发现在我的游戏中，每个人都会出现这种过滤器置乱现象。
我目前的工作是以下功能，这似乎足够了：

public static void fixFixtureFilter(Fixture fixture, short maskBits, short categoryBits) {
    Filter filter = fixture.getFilterData();
    filter.maskBits = maskBits;
    filter.categoryBits = categoryBits;
    fixture.setFilterData(filter);
}

不过，我的b2d世界肯定出了什么问题。