在圆的边缘联合

Question

• 绿色方块是box2d地面。
• 较大的圆圈通过旋转接头连接到地面，并且可以旋转。
• 所有圈子都是b2_dynamicBody

我想在较大圆圈的边缘或边界上连接较小的圆圈，如下所示。 请告诉我如何实现它以及我必须使用什么样的关节？ 此外，当我旋转大圆时，小圆圈应该粘在它的位置。

Answer 1

完成此代码....
//在钩子大圆圈之间创建关节

wheelSprite = [[CCSprite alloc] initWithFile:@"heroWheel.png"];
wheelSprite.visible = FALSE;
wheelSprite.scale = 1.0*hero_size_factor;
wheelSprite.rotation = 0.0;
wheelSprite.anchorPoint = CGPointMake(0.5,0.5);
[layer addChild:wheelSprite z:5];

ballBodyDef.userData = wheelSprite;

//create hook between big circle 

hook = world->CreateBody(&ballBodyDef);

b2PolygonShape hookShape;
hookShape.SetAsBox(0.2,0.1);

b2FixtureDef hookDef;
hookDef.shape=&hookShape;
hookDef.density=0.5f*hero_size_factor;
hookDef.friction = 0.0f;
hookDef.restitution = 0.0f;
hookDef.filter.groupIndex=heroGroupIndex;

hook->CreateFixture(&hookDef);

//create circle shape fixture

b2CircleShape wheel1,wheel2,wheel3,wheel4;

float wheelRadius = hero_width/4.0f;

//Create fixture with above shape
b2FixtureDef ballShapeDef1,ballShapeDef2,ballShapeDef3,ballShapeDef4;
wheel1.m_p = b2Vec2(wheelRadius, wheelRadius);
wheel1.m_radius = wheelRadius;
ballShapeDef1.shape = &wheel1;
ballShapeDef1.density = 0.0f;
ballShapeDef1.friction = 0.0f;
ballShapeDef1.restitution = 0.0f;
ballShapeDef1.filter.groupIndex=heroGroupIndex;
hook->CreateFixture(&ballShapeDef1);



wheel2.m_radius = wheelRadius;
wheel2.m_p = b2Vec2(-wheelRadius, -wheelRadius);

ballShapeDef2.shape = &wheel2;
ballShapeDef2.density = 0.0f;
ballShapeDef2.friction = 0.0f;
ballShapeDef2.restitution = 0.0f;
ballShapeDef2.filter.groupIndex=heroGroupIndex;
hook->CreateFixture(&ballShapeDef2);

wheel3.m_radius = wheelRadius;
wheel3.m_p = b2Vec2(wheelRadius,-wheelRadius);

ballShapeDef3.shape = &wheel3;
ballShapeDef3.density = 0.0f;
ballShapeDef3.friction = 0.0f;
ballShapeDef3.restitution = 0.0f;
ballShapeDef3.filter.groupIndex=heroGroupIndex;
hook->CreateFixture(&ballShapeDef3);


wheel4.m_radius = wheelRadius;
wheel4.m_p = b2Vec2(-wheelRadius,wheelRadius);

ballShapeDef4.shape = &wheel4;
ballShapeDef4.density = 0.0f;
ballShapeDef4.friction = 0.0f;
ballShapeDef4.restitution = 0.0f;
ballShapeDef4.filter.groupIndex=heroGroupIndex;
hook->CreateFixture(&ballShapeDef4);

//Create Revolute Joints between hook and big circle
b2RevoluteJointDef revoluteJointDef;
revoluteJointDef.bodyA = hook;
revoluteJointDef.bodyB = Leg;
revoluteJointDef.collideConnected = false;

revoluteJointDef.localAnchorA.Set(0.0,0.0);
revoluteJointDef.localAnchorB.Set(0.0,-(hero_height - 0.1));
revoluteJointDef.referenceAngle = 0;
revoluteJointDef.maxMotorTorque = 5.0*hero_size_factor;


Hero_Motor = (b2RevoluteJoint*)world->CreateJoint(&revoluteJointDef);