问夹具的Jbox2D问题

EN

//fields
Code:
public static final float METER_IN_PIXELS = 40.0f;
private World world;
...



//constructor
Code:
public Map(int startPosX, int startPosY)
{
   world = new World(new Vec2(0,10.0f));
   ...
}


//called every 33ms
Code:
public void update(int delta)
{
   world.step(1/60.0f, 8, 3);
   player.update(delta); // to update the player's movement
        ...
}

//fields
Code:
private Body body;
private float physicsX;
private float physicsY;

//constructor

public PhysicsMovingEntity(float x, float y, World world)
Code:
{
   super.setX(x);
   super.setY(y);
   physicsX = x / Map.METER_IN_PIXELS;
   physicsY = y / Map.METER_IN_PIXELS;
   initPhysicalBody(world);
}


//init method

Code:
public void initPhysicalBody(World world)
{
   BodyDef bd = new BodyDef();
   bd.type = BodyType.DYNAMIC;
   bd.position.set(physicsX, physicsY);
   bd.gravityScale = 0;
   PolygonShape ps = new PolygonShape();
   ps.setAsBox(getFrameSize().width() / Map.METER_IN_PIXELS, getFrameSize().height() / Map.METER_IN_PIXELS);
   FixtureDef fd = new FixtureDef();
   fd.density = 1;
   fd.shape = ps;
   body = world.createBody(bd);
   [color=#FF4000]body.createFixture(fd);[/color] // this toggles the problem
}


//called every 33ms
Code:
public void update(int delta) 
{
   super.update(delta);
   [color=#FF4000]body.setLinearVelocity(new Vec2(getLastDirection().getX() * getSpeed(), 
         getLastDirection().getY() * getSpeed()));[/color] // probably giving the second problem
}