libgdx-box2D-contactlistener

Question

我正在使用ContactListener测试box 2D中两个物体之间的碰撞

这是我在世界上使用的所有contactListener类。设置ContactListener（new Box2DWorld（this））以添加它

 public class Box2DWorld implements ContactListener{

World world;
GameScreen gameScreen;
Car car;

public enum BodyName{
    frontWheel,rearWheel,carShell,ground,finishSensor
}

/**
 * this class handles collisions and body userdata
 * @param gameScreen
 */
public Box2DWorld(GameScreen gameScreen) {  
    this.gameScreen = gameScreen;
    world = gameScreen.world;
    this.car = gameScreen.car;
}


/*
 * the debug should be like 
 * 
 * BEGONCONTACT,preSolve,postSolve,......postsolve,ENDCONTACT,BEGINCONTACT,preSolve,postSolve
 * 
 * but i am getting debug like
 * 
 * BEGINCONTACT,preSolve,postSolve,......postsolve,BEGINCONTACT,presolve,ENDCONTACT,preSolve,postSolve...
 * 
 * i can't understand why begincontact appears twice without endcontact in between and also bodies are in contact
 *  even after endcontact
 * 
 */

@Override
public void beginContact(Contact contact) {
    BodyName bodyA = (BodyName) contact.getFixtureA().getBody().getUserData();
    BodyName bodyB = (BodyName) contact.getFixtureB().getBody().getUserData();


    if((bodyA == BodyName.frontWheel && bodyB == BodyName.ground )||(bodyA == BodyName.ground && bodyB == BodyName.frontWheel)){
        car.frontWheel.onGround = true;
        System.out.println("begin contact");
    }


}   

@Override
public void endContact(Contact contact) {
    BodyName bodyA = (BodyName) contact.getFixtureA().getBody().getUserData();
    BodyName bodyB = (BodyName) contact.getFixtureB().getBody().getUserData();

    if((bodyA == BodyName.frontWheel && bodyB == BodyName.ground )||(bodyA == BodyName.ground && bodyB == BodyName.frontWheel)){
        car.frontWheel.onGround = false;
        System.out.println("contact end");  
    }

}

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

    BodyName bodyA = (BodyName) contact.getFixtureA().getBody().getUserData();
    BodyName bodyB = (BodyName) contact.getFixtureB().getBody().getUserData();

    if((bodyA == BodyName.frontWheel && bodyB == BodyName.ground )||(bodyA == BodyName.ground && bodyB == BodyName.frontWheel)){
        System.out.println("PreSolve"); 
    }


}

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

    BodyName bodyA = (BodyName) contact.getFixtureA().getBody().getUserData();
    BodyName bodyB = (BodyName) contact.getFixtureB().getBody().getUserData();

    if((bodyA == BodyName.frontWheel && bodyB == BodyName.ground )||(bodyA == BodyName.ground && bodyB == BodyName.frontWheel)){
        System.out.println("postSolve");    
    }

}

我的dedub是这样的

beginContact preSolve postSolve。preSolve postSolve beginContact preSolve END CONTACT postSolve preSolve。

我不明白为什么begincontact出现在endcontact之前

地面和前轮车身各只有1个夹具

我一周都搞不懂，请帮帮我

Answer 1

请记住，接触是在两个固定装置之间，而不是两个实体之间。

我猜你的地面是由许多固定装置组成的，它们都在同一个地面上，对吗？当车轮在固定装置上滚动时，它一次可以接触到多个固定装置，所以你可以按这个顺序开始（固定装置1）、开始（固定装置2）、结束（固定装置1）。这很正常。我想如果你打印出每个接触事件中涉及的地面固定装置，你会明白我的意思。

如果您想知道车轮何时接触地面，则需要跟踪当前接触的固定装置总数。您可以通过在获得“开始”事件时递增计数器，在获得“结束”事件时递减计数器来实现这一点。然后，您可以随时检查计数器，如果计数器大于零，则车轮接触地面。