Question

我正在使用cocos2d-x 3.x和box2d制作突破性游戏，引用http://www.raywenderlich.com/

我的游戏逻辑就是这个。

在init中，调用StartGame函数。在这里，我使用ApplyLinearImpulse移动球。
如果球击中底壁，球会停止移动。
单击屏幕，然后调用StartGame函数，再次转换球的位置和ApplyLinearImpulse。
重复编号2和3

问题是球的速度在1号时与其他人的结果不同，即使我给予同样的力量。在开始时球的速度很慢但是在一个循环之后，球的速度非常快。我不知道为什么......我需要帮助。这是我的源代码。

#include "GameScene.h"


#define PTM_RATIO 32

USING_NS_CC;

Scene* GameScene::createScene() {

    Scene* scene = Scene::create();
    Layer* layer = GameScene::create();

    scene->addChild(layer);
    return scene;
}

bool GameScene::init() {

    if(!Layer::init()){
        return false;
    }

    Size visibleSize = Director::getInstance()->getVisibleSize();
    // Create a world
    b2Vec2 gravity = b2Vec2(0.0f, 0.0f);
    _world = new b2World(gravity);

    // create contact listener
    _contactListener = new MyContactListener();
    _world->SetContactListener(_contactListener);

    CreateWall(visibleSize);
    CreateBall();
    CreatePaddle(visibleSize);

    label = LabelTTF::create("Game Over", "Arial", 32);
    label->setColor(Color3B(255,255,255));
    label->setPosition(Point(visibleSize.width/2, visibleSize.height/2));
    this->addChild(label);

    b2PrismaticJointDef jointDef;
    b2Vec2 worldAxis(1.0f, 0.0f);
    jointDef.collideConnected = true;
    jointDef.Initialize(_paddleBody, _groundBody, _paddleBody->GetWorldCenter(), worldAxis);
    _world->CreateJoint(&jointDef);



    // add touch events
    auto dispatcher = Director::getInstance()->getEventDispatcher();
    _touchListener = EventListenerTouchOneByOne::create();
    _touchListener->onTouchBegan = CC_CALLBACK_2(GameScene::onTouchBegan, this);
    _touchListener->onTouchMoved = CC_CALLBACK_2(GameScene::onTouchMoved, this);
    _touchListener->onTouchCancelled = CC_CALLBACK_2(GameScene::onTouchCancelled, this);
    _touchListener->onTouchEnded = CC_CALLBACK_2(GameScene::onTouchEnded, this);
    dispatcher->addEventListenerWithSceneGraphPriority(_touchListener, this);

    Director::getInstance()->getScheduler()->scheduleSelector(schedule_selector(GameScene::tick), this, 1/60, false);

    StartGame(0);

    return true;
}

void GameScene::tick(float dt) {
    _world->Step(dt, 10, 10);
    if(!gameOver) {

        for(b2Body *b = _world->GetBodyList(); b; b = b->GetNext()) {
            if(b->GetUserData() != NULL) {
                Sprite *s = static_cast<Sprite*>(b->GetUserData());
                if(s->getTag() == 1) {
                    b2Vec2 velocity =  b->GetLinearVelocity();
                    float32 speed = velocity.Length();
                    if(speed > maxSpeed)
                        b->SetLinearDamping(0.5f);
                    else if(speed < maxSpeed)
                        b->SetLinearDamping(0.0f);
                }
                s->setPosition(Point(b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO));
                s->setRotation(-1 * CC_RADIANS_TO_DEGREES(b->GetAngle()));
            }
        }
        for_each(_contactListener->_contacts.begin(), _contactListener->_contacts.end(),
                 [&](MyContact contact) {
                     if(contact.contain(_bottomFixture, _ballFixture)) {
                         cocos2d::log("Ball hit Bottom");
                         GameOver();
                     }
                 } );
    }
}

bool GameScene::onTouchBegan(Touch *touch, Event *event){
    if(gameOver) {
        StartGame(1);
        return true;
    }

    if(_mouseJoint != NULL) return true;
    cocos2d::log("touch began test");
    Point location = touch->getLocation();
    b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);

    if(_paddleFixture->TestPoint(locationWorld)) {
        b2MouseJointDef md;
        md.bodyA = _groundBody;
        md.bodyB = _paddleBody;
        md.target = locationWorld;
        md.collideConnected = true;
        md.maxForce = 1000.0f * _paddleBody->GetMass();

        _mouseJoint = static_cast<b2MouseJoint*>(_world->CreateJoint(&md));
        _paddleBody->SetAwake(true);
    }

    return true;
}

void GameScene::onTouchMoved(Touch *touch, Event *event) {

    if(_mouseJoint == NULL) return;

    Point location = touch->getLocation();
    b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);

    _mouseJoint->SetTarget(locationWorld);
}

void GameScene::onTouchCancelled(Touch *touch, Event *event) {

    if(_mouseJoint) {
        _world->DestroyJoint(_mouseJoint);
        _mouseJoint = NULL;
    }
}

void GameScene::onTouchEnded(Touch *touch, Event *event) {
    if(_mouseJoint) {
        _world->DestroyJoint(_mouseJoint);
        _mouseJoint = NULL;
    }
}

void GameScene::CreateWall(Size visibleSize) {
    // Create edges around the entire class
    b2BodyDef groundBodyDef;
    groundBodyDef.position.Set(0, 0);
    _groundBody = _world->CreateBody(&groundBodyDef);

    b2EdgeShape groundBox;
    b2FixtureDef groundBoxDef;
    groundBoxDef.shape = &groundBox;

    groundBox.Set(b2Vec2(0,0), b2Vec2(visibleSize.width/PTM_RATIO,0));
    _bottomFixture  = _groundBody->CreateFixture(&groundBoxDef);

    groundBox.Set(b2Vec2(0,0), b2Vec2(0,visibleSize.height/PTM_RATIO));
    _groundBody->CreateFixture(&groundBoxDef);

    groundBox.Set(b2Vec2(0,visibleSize.height/PTM_RATIO), b2Vec2(visibleSize.width/PTM_RATIO,visibleSize.height/PTM_RATIO));
    _groundBody->CreateFixture(&groundBoxDef);

    groundBox.Set(b2Vec2(visibleSize.width/PTM_RATIO,visibleSize.height/PTM_RATIO), b2Vec2(visibleSize.width/PTM_RATIO,0));
    _groundBody->CreateFixture(&groundBoxDef);

}

void GameScene::CreateBall() {

    // create ball texture
    ball = Sprite::create("ball.png");
    ball->setPosition(Point(100,100));
    ball->setTag(1);
    this->addChild(ball);

    // create ball body
    b2BodyDef ballBodyDef;
    ballBodyDef.type = b2_dynamicBody;
    ballBodyDef.position.Set(100/PTM_RATIO, 100/PTM_RATIO);
    ballBodyDef.angle = 0;
    ballBodyDef.userData = ball;
    ballBody = _world->CreateBody(&ballBodyDef);

    // create circle shape
    b2CircleShape circle;
    circle.m_radius = 26.0/PTM_RATIO;

    //create shape definition and add to body
    b2FixtureDef ballShapeDef;
    ballShapeDef.shape = &circle;
    ballShapeDef.density = 1.0f;
    ballShapeDef.friction = 0.0f;
    ballShapeDef.restitution = 1.0f;
    _ballFixture = ballBody->CreateFixture(&ballShapeDef);
}

void GameScene::CreatePaddle(Size visibleSize) {
    //create paddle
    userPaddle = Sprite::create("paddle.png");
    userPaddle->setPosition(Point(visibleSize.width/2, 50));
    this->addChild(userPaddle);

    // create paddle body
    b2BodyDef paddleBodyDef;
    paddleBodyDef.type = b2_dynamicBody;
    paddleBodyDef.position.Set(visibleSize.width/2/PTM_RATIO, 50/PTM_RATIO);
    paddleBodyDef.userData = userPaddle;
    _paddleBody = _world->CreateBody(&paddleBodyDef);

    // create paddle shape
    b2PolygonShape paddleShape;
    paddleShape.SetAsBox(userPaddle->getContentSize().width/2/PTM_RATIO, userPaddle->getContentSize().height/2/PTM_RATIO);

    // create shape definition and add to body
    b2FixtureDef paddleShapeDef;
    paddleShapeDef.shape = &paddleShape;
    paddleShapeDef.density = 10.0f;
    paddleShapeDef.friction = 0.4f;
    paddleShapeDef.restitution = 0.1f;
    _paddleFixture = _paddleBody->CreateFixture(&paddleShapeDef);

}

void GameScene::GameOver() {

    gameOver = true;
    _world->ClearForces();
    ballBody->SetAngularVelocity(0);
    ballBody->SetLinearVelocity(b2Vec2(0,0));
    ballBody->SetLinearDamping(0);
    label->setVisible(true);

}

void GameScene::StartGame(int stage) {

    ballBody->SetTransform(b2Vec2(100/PTM_RATIO, 100/PTM_RATIO), 0);
    b2Vec2 force = b2Vec2(150,150);
    //ballBody->ApplyForceToCenter(force);
    ballBody->ApplyLinearImpulse(force, ballBody->GetWorldCenter());
    gameOver = false;
    label->setVisible(false);
}

GameScene::~GameScene() {
    delete _world;
    delete _contactListener;
    _groundBody = NULL;
}

ApplyLinearImpulse的结果与第一个结果不同 - Box2D

0 个答案: