在Cocos2D iPhone中將動態B2body固定在地面上

Question

我已經開始研究繩索物理。以某種方式，我使用Revolute關節創建了繩索。 我已經實現了一根繩子與一個圓形b2body相連，現在我想將一根繩子的一端固定在屏幕頂部，但是我使用了動態物體，因此我很難將其固定在屏幕頂部。我確實需要在這方面有所幫助，最近幾天我堅持下來。

這是我充滿活力的身體：

b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
b2Vec2 startPos = [self toMeters:ccp(s.width/2 ,s.height)];
bodyDef.position = startPos;
b2FixtureDef fixtureDef;
fixtureDef.density = 0.1;
b2PolygonShape polygonShape;
polygonShape.SetAsBox(linkWidth,linkHeight);
fixtureDef.shape = &polygonShape;

關節：

 b2Body* mylink = world->CreateBody( &bodyDef1 );
 mylink->CreateFixture( &fixtureDef1 );

 b2RevoluteJointDef revoluteJointDef;
 revoluteJointDef.bodyA = mylink;        
 revoluteJointDef.bodyB = link;

revoluteJointDef.localAnchorA.Set( 0,  linkHeight);
revoluteJointDef.localAnchorB.Set( 0, -linkHeight);

繩索體：

對於（int i = 0; i <10; i ++）{

    b2Body* newLink = world->CreateBody( &bodyDef );
    newLink->CreateFixture( &fixtureDef );
    PhysicsSprite* segmentSprite = [PhysicsSprite spriteWithFile:@"rope_seg_new2.png"];
    [self addChild:segmentSprite];
    [segmentSprite setPhysicsBody:link];

    revoluteJointDef.bodyA = link;
    revoluteJointDef.bodyB = newLink;
    world->CreateJoint( &revoluteJointDef );

    link = newLink;  //prepare for next iteration
}

最終我以這種方式連接了我的圓形動態身體：

PhysicsSprite* circleBodySprite = [PhysicsSprite spriteWithFile:@"medal1.png"];

[self addChild:circleBodySprite z:1];

b2CircleShape circleShape;
circleShape.m_radius = circleBodySprite.contentSize.width/2 / PTM_RATIO;
fixtureDef.shape  = &circleShape;
fixtureDef.density =0.5;   
b2Body* chainBase =world->CreateBody( &bodyDef );
chainBase->CreateFixture( &fixtureDef );
[circleBodySprite setPhysicsBody:chainBase];
balloon = chainBase;


//another revolute joint to connect the chain(of ropes ) to the circle 

revoluteJointDef.bodyA = link;        //the last added link of the chain
revoluteJointDef.bodyB = chainBase;

//the regular position for chain link joints, as above

revoluteJointDef.localAnchorA.Set(0,linkWidth);

//a little in from the edge of the circle

revoluteJointDef.localAnchorB.Set(0,linkWidth);

world->CreateJoint( &revoluteJointDef );

// toMeters在這里打電話

-（b2Vec2）至米：（CGPoint）point {返回b2Vec2（point.x / PTM_RATIO，point.y / PTM_RATIO）;

}

請幫忙 ..

Answer 1

// Restrict paddle along the x axis
b2PrismaticJointDef jointDef;
b2Vec2 worldAxis(1.0f, 0.0f);
jointDef.collideConnected = true;
jointDef.Initialize(_paddleBody, _groundBody, 
_paddleBody->GetWorldCenter(), worldAxis);
_world->CreateJoint(&jointDef);

此代碼取自raywenderlich的網站，他在該網站上講述了如何制作box2d突破游戲。此處為鏈接http://www.raywenderlich.com/28604/how-to-create-a-breakout-game-with-box2d -and-cocos2d-2-x-tutorial-part-1 。

現在我無法完全理解您想要做什么，但是我認為這可能會有所幫助。