libgdx box2d body -如何在特定方向上以恒定的速度移动body？

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.physics.box2d.Body;
import com.badlogic.gdx.physics.box2d.BodyDef;
import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer;
import com.badlogic.gdx.physics.box2d.FixtureDef;
import com.badlogic.gdx.physics.box2d.PolygonShape;
import com.badlogic.gdx.physics.box2d.World;

public class MyGame extends ApplicationAdapter {
    private World world;
    private Box2DDebugRenderer debugRenderer;
    private OrthographicCamera camera;
    private Body body;

    @Override
    public void create() {
        world = new World(new Vector2(0, -9.8f), true);
        debugRenderer = new Box2DDebugRenderer();
        camera = new OrthographicCamera(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        camera.position.set(camera.viewportWidth / 2, camera.viewportHeight / 2, 0);

        // 创建一个box2d的body对象
        BodyDef bodyDef = new BodyDef();
        bodyDef.type = BodyDef.BodyType.DynamicBody;
        bodyDef.position.set(0, 0);
        body = world.createBody(bodyDef);

        // 创建一个box2d的形状对象，并设置其大小
        PolygonShape shape = new PolygonShape();
        shape.setAsBox(1, 1);

        // 创建一个box2d的fixture对象，并将形状设置给它
        FixtureDef fixtureDef = new FixtureDef();
        fixtureDef.shape = shape;

        // 将fixture对象附加到body上
        body.createFixture(fixtureDef);

        // 设置body的线性速度，实现在特定方向上以恒定速度移动
        float speed = 5f; // 移动速度
        Vector2 direction = new Vector2(1, 0); // 移动方向
        direction.nor(); // 将方向向量归一化
        Vector2 velocity = direction.scl(speed); // 计算速度向量
        body.setLinearVelocity(velocity);

        shape.dispose();
    }

    @Override
    public void render() {
        Gdx.gl.glClearColor(0, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        world.step(Gdx.graphics.getDeltaTime(), 6, 2);

        camera.update();
        debugRenderer.render(world, camera.combined);
    }

    @Override
    public void dispose() {
        world.dispose();
        debugRenderer.dispose();
    }
}