box2d类分析：ContactFilter

public class ContactFilter {
    public boolean shouldCollide(Fixture fixtureA, Fixture fixtureB){
        Filter filterA = fixtureA.getFilterData();
        Filter filterB = fixtureB.getFilterData();

        if (filterA.groupIndex == filterB.groupIndex && filterA.groupIndex != 0){
            return filterA.groupIndex > 0;
        }

        boolean collide = (filterA.maskBits & filterB.categoryBits) != 0 &&
                          (filterA.categoryBits & filterB.maskBits) != 0;
        return collide;
    }
}

碰撞过滤，如果碰撞发生了就返回true.它主要是通过判断刚体所在的组以及位信息，两个刚体是否会发生碰撞。