如何设置精灵在 box2d 体内的位置？

Question

基本上我的身体有 2 个多边形。当我为 userData 添加精灵时，纹理的位置不是我想要的位置。我想做的是调整纹理在体内的位置。这是我设置此内容的代码示例：

CCSpriteSheet *sheet = (CCSpriteSheet*) [self getChildByTag:kTagSpriteSheet];
CCSprite *pigeonSprite = [CCSprite spriteWithSpriteSheet:sheet rect:CGRectMake(0,0,40,32)];
[sheet addChild:pigeonSprite z:0 tag:kPigeonSprite];

pigeonSprite.position = ccp( p.x, p.y);

bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);
bodyDef.userData = sprite;
b2Body *body = world->CreateBody(&bodyDef);

b2CircleShape dynamicCircle;
dynamicCircle.m_radius = .25f;
dynamicCircle.m_p.Set(0.0f, 1.0f);

        // Define the dynamic body fixture.
b2FixtureDef circleDef;
circleDef.shape = &dynamicCircle;   
circleDef.density = 1.0f;
circleDef.friction = 0.3f;

body->CreateFixture(&circleDef);

b2Vec2 vertices[3];
vertices[0].Set(-0.5f, 0.0f);
vertices[1].Set(0.5f, 0.0f);
vertices[2].Set(0.0f, 1.0f);
b2PolygonShape triangle;
triangle.Set(vertices, 3);

b2FixtureDef triangleDef1;
triangleDef1.shape = ▵ 
triangleDef1.density = 1.0f;
triangleDef1.friction = 0.3f;

body->CreateFixture(&triangleDef1);

Answer 1

我对 Objective-C 不太熟悉，但我会尝试一下。

我所能看到的是，您正在将指向精灵对象的指针存储在主体的用户数据中，然后将其留在那里。如果您希望将身体的位置转移到精灵上，则需要每帧更新它。

在 C++ 中，这看起来像这样。

// To be called each time physics should be updated.
void physicsStep(float32 timeStep, int32 velocityIterations, int32 positionIterations) {
    // This is the usual update routine.
    world.Step(timeStep, velocityIterations, positionIterations);
    world.ClearForces();

    // SpriteClass can be replaced with any class you favor.
    // Assume there is a known pointer to the b2Body. Otherwise you'll have to get that,
    // or iterate over all bodies in the world.
    SpriteClass *sprite = (SpriteClass*)body->GetUserData();

    // Once you have the pointer you can transfer all the data.
    sprite.position = body->GetPosition();
    sprite.angle = body->GetAngle();
    // ... and so on
}

用户数据只是 b2Body 中的任意存储空间，Box2D 不知道您决定在那里存储什么。

Answer 2

要随身体移动精灵，则必须根据身体设置精灵位置

在您的更新方法中

在你的COCOS2D-X
这里

sprite = static_cast<CCSprite*>body->GetUserData();
sprite->setPosition(vec2(body->GetPosition().x*PTM_RATIO, body->GetPosition().y*PTM_RATIO));
sprite->setRotation(-CC_Radian_to_Degree(body->GetAngle));

PTM_RATIO = 32；