java 如何使用 libgdx 联系人监听器

how to use the libgdx contactlistener

提问by Xerusial

I've just began to work with the Libgdx's Box2d Engine but i simply do not understand when the methods of the Contactlistenershould be called. There is on the one hand "begin contact" and on the other "end contact". Where should i call them, to get the Number of of a certain fixture touching others? And how do I implement the Contactlistener? A redirec' to a Tutorial would answer my Question. I didn't find anything while searching google. This onehelped me a lot but it is written for C++ and does not refer to the implementation into a main-gamecircle. Thx for helping me ;)

我刚刚开始使用 Libgdx 的 Box2d 引擎，但我根本不明白什么时候应该调用Contactlistener的方法。一方面是“开始接触”，另一方面是“结束接触”。我应该在哪里打电话给他们，以获得某个灯具接触其他灯具的数量？以及如何实现Contactlistener？重定向到教程将回答我的问题。我在谷歌搜索时没有找到任何东西。这一个对我帮助很大，但它是对C ++编写，并没有指执行到主gamecircle。感谢帮助我;)

回答by Rod Hyde

Here's a short example for libgdx. It shows how to create a ContactListenerto show which fixtures are involved when contacts are made and broken. It also shows the use of world.getContactList()which will return a list of contacts that still exist after the physics step. This may miss contacts that were made and broken during the course of the physics step. If you are interested in these then you will want to implement a ContactListener, using beginContact()to detect when contacts are made and endContact()to detect when they are broken.

这是 libgdx 的一个简短示例。它展示了如何创建ContactListener以显示在建立和断开接触时涉及哪些装置。它还显示了world.getContactList()的使用，它将返回一个在物理步骤之后仍然存在的联系人列表。这可能会错过在物理步骤过程中建立和断开的接触。如果您对这些感兴趣，那么您将需要实现一个ContactListener，使用beginContact()来检测何时建立联系并使用endContact()来检测它们何时被破坏。

package hacks;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.math.MathUtils;
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.BodyDef.BodyType;
import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer;
import com.badlogic.gdx.physics.box2d.Contact;
import com.badlogic.gdx.physics.box2d.ContactImpulse;
import com.badlogic.gdx.physics.box2d.ContactListener;
import com.badlogic.gdx.physics.box2d.Fixture;
import com.badlogic.gdx.physics.box2d.FixtureDef;
import com.badlogic.gdx.physics.box2d.Manifold;
import com.badlogic.gdx.physics.box2d.PolygonShape;
import com.badlogic.gdx.physics.box2d.World;

public class Box2DDemoMain extends com.badlogic.gdx.Game {

    private static final float SCALING = 0.1f;

    private Box2DDebugRenderer debugRenderer;
    private OrthographicCamera camera;
    private World world;

    @Override
    public void create() {
        debugRenderer = new Box2DDebugRenderer();
        camera = new OrthographicCamera();

        createWorld();
        createCollisionListener();
        createGround();
        createBox();
    }

    private void createWorld() {
        Vector2 gravity = new Vector2(0, -10);
        world = new World(gravity, true);
    }

    private void createCollisionListener() {
        world.setContactListener(new ContactListener() {

            @Override
            public void beginContact(Contact contact) {
                Fixture fixtureA = contact.getFixtureA();
                Fixture fixtureB = contact.getFixtureB();
                Gdx.app.log("beginContact", "between " + fixtureA.toString() + " and " + fixtureB.toString());
            }

            @Override
            public void endContact(Contact contact) {
                Fixture fixtureA = contact.getFixtureA();
                Fixture fixtureB = contact.getFixtureB();
                Gdx.app.log("endContact", "between " + fixtureA.toString() + " and " + fixtureB.toString());
            }

            @Override
            public void preSolve(Contact contact, Manifold oldManifold) {
            }

            @Override
            public void postSolve(Contact contact, ContactImpulse impulse) {
            }

        });
    }

    private void createGround() {
        PolygonShape groundShape = new PolygonShape();
        groundShape.setAsBox(50, 1);
        BodyDef groundBodyDef = new BodyDef();
        groundBodyDef.type = BodyType.StaticBody;
        groundBodyDef.position.set(0, -20);
        Body groundBody = world.createBody(groundBodyDef);
        FixtureDef fixtureDef = new FixtureDef();
        fixtureDef.shape = groundShape;
        groundBody.createFixture(fixtureDef);
        groundShape.dispose();
    }

    private void createBox() {
        PolygonShape boxShape = new PolygonShape();
        boxShape.setAsBox(1, 1);
        BodyDef boxBodyDef = new BodyDef();
        boxBodyDef.position.set(0, 20);
        boxBodyDef.angle = MathUtils.PI / 32;
        boxBodyDef.type = BodyType.DynamicBody;
        boxBodyDef.fixedRotation = false;
        Body boxBody = world.createBody(boxBodyDef);
        FixtureDef boxFixtureDef = new FixtureDef();
        boxFixtureDef.shape = boxShape;
        boxFixtureDef.restitution = 0.75f;
        boxFixtureDef.density = 2.0f;
        boxBody.createFixture(boxFixtureDef);
        boxShape.dispose();
    }

    @Override
    public void resize(int width, int height) {
        super.resize(width, height);
        float cameraWidth = Gdx.graphics.getWidth() * SCALING;
        float cameraHeight = Gdx.graphics.getHeight() * SCALING;
        camera.setToOrtho(false, cameraWidth, cameraHeight);
        camera.position.set(0, 0, 0);
    }

    @Override
    public void render() {
        super.render();

        world.step(Gdx.graphics.getDeltaTime(), 8, 3);

        int numContacts = world.getContactCount();
        if (numContacts > 0) {
            Gdx.app.log("contact", "start of contact list");
            for (Contact contact : world.getContactList()) {
                Fixture fixtureA = contact.getFixtureA();
                Fixture fixtureB = contact.getFixtureB();
                Gdx.app.log("contact", "between " + fixtureA.toString() + " and " + fixtureB.toString());
            }
            Gdx.app.log("contact", "end of contact list");
        }

        Gdx.gl.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        camera.update();
        debugRenderer.render(world, camera.combined);
    }

    public static void main(String[] args) {
        LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();

        config.title = Box2DDemoMain.class.getName();
        config.width = 800;
        config.height = 480;
        config.fullscreen = false;
        config.useGL20 = true;
        config.useCPUSynch = true;
        config.forceExit = true;
        config.vSyncEnabled = true;

        new LwjglApplication(new Box2DDemoMain(), config);
    }
}

回答by Pranav008

you dont have to call those methods anywhere. just create a class and implement ContactListener in it. now in your code just use world.setContactListener(ContactListener listener) .

您不必在任何地方调用这些方法。只需创建一个类并在其中实现 ContactListener 即可。现在在您的代码中只需使用 world.setContactListener(ContactListener listener) 。

Whenever collision occur in your world, all 4 methods will be called . You will get fixtureA and fixtureB of 2 colliding bodies

每当您的世界中发生碰撞时，所有 4 个方法都将被调用。你会得到两个碰撞体的fixtureA和fixtureB