applyLinearImpulse無法正常工作（Box2d）？

Question

我正在使用ContactListener偵聽任何接觸，並且如果在球與地面之間檢測到碰撞，則該球應獲得向上的沖動，這在ContactListener類的void endContact()函數中提供。 但是，對於任何沖動值，這種沖動根本沒有作用。 對於任何沖量值，球都會以相同的距離反彈。 我究竟做錯了什么。 這是完整的代碼：

public class Game implements ApplicationListener {
     World world ;  
     Box2DDebugRenderer debugRenderer;  
     OrthographicCamera camera;  
     static final float BOX_STEP=1/60f;  
     static final int BOX_VELOCITY_ITERATIONS=8;  
     static final int BOX_POSITION_ITERATIONS=3;  
     static final float WORLD_TO_BOX=0.01f;  
     static final float BOX_WORLD_TO=100f;  
     Rectangle ball;
     Body body;

    @Override  
     public void create() {
          world = new World(new Vector2(0, -100), true);
          camera = new OrthographicCamera(); 

          camera.viewportHeight = 480;  
          camera.viewportWidth = 800;  
          camera.position.set(camera.viewportWidth * .5f, camera.viewportHeight * .5f, 0f);  
          camera.update();

          //Ground body  
          BodyDef groundBodyDef =new BodyDef();  
          groundBodyDef.position.set(new Vector2(0, 10));  
          Body groundBody = world.createBody(groundBodyDef);  
          PolygonShape groundBox = new PolygonShape();  
          groundBox.setAsBox((camera.viewportWidth) * 2, 10.0f);  
          groundBody.createFixture(groundBox, 0.0f);  

          //Dynamic Body  
          BodyDef bodyDef = new BodyDef();  
          bodyDef.type = BodyType.DynamicBody;  
          bodyDef.position.set(camera.viewportWidth / 8, camera.viewportHeight / 2);  
          body = world.createBody(bodyDef); 

          // create a Rectangle to logically represent the ball
          CircleShape dynamicCircle = new CircleShape();  
          dynamicCircle.setRadius(40f);  
          FixtureDef fixtureDef = new FixtureDef();  
          fixtureDef.shape = dynamicCircle;  
          fixtureDef.density = 1.0f;  
          fixtureDef.friction = 0.0f;  
          fixtureDef.restitution =1f;
          body.createFixture(fixtureDef);
          debugRenderer = new Box2DDebugRenderer();  

          listener listener1=new listener();
          world.setContactListener(listener1);
     }
     @Override  
     public void render() {            
          Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);  
          debugRenderer.render(world, camera.combined);  
          world.step(BOX_STEP, BOX_VELOCITY_ITERATIONS, BOX_POSITION_ITERATIONS);


     }  
     class listener implements ContactListener 
     {

        @Override
        public void beginContact(Contact contact) {
            // TODO Auto-generated method stub

        }

        @Override
        public void endContact(Contact contact) {
            // TODO Auto-generated method stub
            body.applyLinearImpulse(0, 500000f, body.getWorldCenter().x, body.getWorldCenter().y, true);
            //body.setLinearVelocity(0,50000000);
            System.out.println("Collision detected");
        }

        @Override
        public void preSolve(Contact contact, Manifold oldManifold) {
            // TODO Auto-generated method stub

        }

        @Override
        public void postSolve(Contact contact, ContactImpulse impulse) {
            // TODO Auto-generated method stub

        } 

     }; 

     @Override  
     public void resize(int width, int height) {  
     }  
     @Override  
     public void pause() {  
     }  
     @Override  
     public void resume() {  
     }  
     @Override  
     public void dispose() {  
     }  
}

Answer 1

在原始的C ++版本中，EndContact在Step函數內部被調用，這是您無法更改世界上任何東西的時間，因為引擎仍在使用它。 我認為Java版本是相同的。 您可能需要記下球已反彈的事實，並在步驟完成后施加脈沖。

Answer 2

對沖動沒有影響的原因是您嘗試在端接法中施加沖動。

在box2d ContactListener方法中，無法更改主體的屬性或位置。

你可以這樣

boolean b;
 @Override
    public void endContact(Contact contact) {
        // TODO Auto-generated method stub
        //body.applyLinearImpulse(0, 500000f, body.getWorldCenter().x, body.getWorldCenter().y, true);
        //body.setLinearVelocity(0,50000000);
       b = true;
        System.out.println("Collision detected");
    }

在您更新方法.....

if(b)
{
  body.applyLinearImpulse(0, 500000f, body.getWorldCenter().x, body.getWorldCenter().y, true);
}