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我正在创建 box2d 多边形，我想在将夹具连接到身体的方法之外创建夹具，但是当我这样做时，我会遇到访问冲突。

我已经逐步完成了代码，box2d 肯定正在获取夹具对象。

当我将夹具连接到方法内的主体时，它工作正常。当我尝试调用方法时，它会引发访问冲突错误

    b2FixtureDef* LineSegment::GenerateFixture(b2Vec2 vertices[4],b2Body* body,b2World* world){
    b2BodyDef bodyDef;
    //bodyDef.type = b2_kinematicBody;
    bodyDef.position.Set(_currentStepStartPosition.x,_currentStepStartPosition.y);
    body =world->CreateBody(&bodyDef);
    int32 count = 4;
    b2PolygonShape polygon;
    polygon.Set(vertices, count);
    b2FixtureDef fixtureDef2;
    fixtureDef2.shape = &polygon;
    fixtureDef2.density = 1.0f;
    fixtureDef2.friction = 0.3f;
    body->CreateFixture(&fixtureDef2);/// works if i attatch the fixture here here
    return &fixtureDef2;
}

当我在这里附加夹具时调用方法失败

    bool LineSegment::GenerateNextBody(b2Body* retBody){
    b2BodyDef bodyDef;
    bodyDef.type = b2_staticBody;
    bodyDef.position.Set(_currentStepStartPosition.x,_currentStepStartPosition.y);
    retBody =world->CreateBody(&bodyDef);
    _currentStep++;
    b2Vec2 vertices[4];
    if(_inclinePerStep != 0){
    GetVertsInclineSquare(vertices,_stepWidth,_thickness,_inclinePerStep);
    }else{
        GetVertsSquare(vertices,_stepWidth,_thickness);
    }
    if(_currentStep == 1){
        _GameWorldVerticies[0] =b2Vec2((_currentStepStartPosition.x+vertices[0].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[0].y)*PTM_RATIO);
        _GameWorldVerticies[3] =b2Vec2((_currentStepStartPosition.x+vertices[3].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[3].y)*PTM_RATIO);

    }
    b2FixtureDef* fixture = GenerateFixture(vertices,retBody,world);

    //retBody->CreateFixture(fixture); throws a access violation if i attatch the fixture here
    _currentStepStartPosition.x += vertices[2].x+(vertices[2].x);
    _currentStepStartPosition.y +=(_inclinePerStep/2);
    if(_steps <= _currentStep){
        _GameWorldVerticies[1] =b2Vec2((_currentStepStartPosition.x+vertices[1].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[1].y)*PTM_RATIO);
        _GameWorldVerticies[2] =b2Vec2((_currentStepStartPosition.x+vertices[2].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[2].y)*PTM_RATIO);
        return false;
    }
    return true;
}

更新

新片段

        b2FixtureDef* fixtureDef2 = new b2FixtureDef();
    fixtureDef2->shape = &polygon;
    fixtureDef2->density = 1.0f;
    fixtureDef2->friction = 0.3f;
    //body->CreateFixture(&fixtureDef2);/// works if i attatch the fixture here here
    return fixtureDef2;
4

1 回答 1

2

问题是您返回一个指向局部变量 in 的指针GenerateFixture，这是未定义的行为。该变量fixtureDef2在堆栈上，当函数返回时，堆栈的该区域不再有效。当您延迟调用该CreateFixture函数时，指针现在将指向该函数的堆栈区域。

要解决这个问题，您可以使用例如在堆上创建它new。

于 2012-08-30T11:10:54.343 回答