Box2d SDL无法在动态身体上应用世界设​​置

Question

设置世界后，我的动态身体不会摔倒。它并不遵循重力。即使我对身体施加力量也不行。

b2Vec2 gravity(0.0f, -9.8f); 
b2World world(gravity); 

//PineCone 
class PineCone 
{ 
    private: 
     //Surface box 
     SDL_Rect box; 

     //Real position 
     float rX, rY; 

     //Velocity 
     float xVel, yVel; 

     //Physics world 
     b2World* world; 

     //Body 
     b2Body* pBodyPineCone; 

    public: 
     //Specify 
     void specify(int w, int h, SDL_Surface* source, SDL_Surface* dest, b2World* world); 

     //Input 
     void handle_input(); 

     //Motion 
     void updatepos(); 
     //void checkStanding(SDL_Rect env[], int N_SOLIDS); 

     //Render 
     void show(); 
}; 

void PineCone::specify(int w, int h, SDL_Surface* source, SDL_Surface* dest, b2World* world) 
{ 

    //Source 
    pPineCone = source; 

    //Destination 
    pScreen = dest; 

    // Define the dynamic pinecone. We set its position and call the body factory. 
    b2BodyDef bodyDef; 
    bodyDef.type = b2_dynamicBody; 

    // Define a ball shape for our dynamic body. 
    b2CircleShape dynamicPineCone; 
    dynamicPineCone.m_p.Set(0, 0); //position, relative to body position 
    dynamicPineCone.m_radius = 0.5; //radius 

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

    // Add the shape to the body. 
    bodyDef.position.Set(0, 20); 
    pBodyPineCone = world->CreateBody(&bodyDef); 
    pBodyPineCone->CreateFixture(&fixtureDef); 
} 

void PineCone::show() 
{ 
    int blit = SDL_BlitSurface(pPineCone, NULL, pScreen, &box); 

    if(blit < 0) 
    { 
     exit(1); 
    } 
} 

我不确定我是否错过了Main中的某些东西。

int main(int argc, char *argv[]) 
{ 
    B2_NOT_USED(argc); 
    B2_NOT_USED(argv); 

    // Prepare for simulation. Typically we use a time step of 1/60 of a 
    // second (60Hz) and 10 iterations. This provides a high quality simulation 
    // in most game scenarios. 
    float32 timeStep = 1.0f/60.0f; 
    int32 velocityIterations = 6; 
    int32 positionIterations = 2; 

    // Start the timer 
    g_dwStartTicks = SDL_GetTicks(); 


    init(); 
    load_files(); 

    //PineCone 
    PineCone myPineCone; 
    myPineCone.specify(g_iPineConeSize, g_iPineConeSize, pPineCone, pScreen, &world); 

    // 
    // The Main Game Loop 
    // 

    do 
    { 
     // Record the current time 
     g_dwStartTime = SDL_GetTicks(); 

     // 
     // Handle they keyboard events here 
     // 
     while (SDL_PollEvent(&event) > 0) 
     { 
      if (event.type == SDL_QUIT) 
      { 
       // Quit event! (Window close, kill signal, etc.) 
       g_iLoopDone = TRUE; 
      } 
     } 

     world.Step(timeStep, velocityIterations, positionIterations); 

     myPineCone.handle_input(); 

     if (g_bPlaying || g_bEnd) 
     {  
      //Show pinecone 
      myPineCone.show(); 
     } 

     // Update the display 
     SDL_Flip(pScreen); 

     g_dwEndTime = SDL_GetTicks(); 
     if (g_dwEndTime < g_dwStartTime + (1000/60)) 
     { 
      SDL_Delay(g_dwStartTime + (1000/60) - g_dwEndTime); 
     } 
    }while (!g_iLoopDone); 

    //Clean Up 
    clean_up(); 

    return 0; 
} 

Answer 1

I can think for example that the physical self is updating're not visualizing 
what the Sprite (Image) not update the corresponding value of its physical body. 
Try to give it a Box2D body position if the image does not move you do not 
have to be the update of physics. 

Try this: 

void setL1b2SpritePosition(Point position) 
{ 
    pBodyPineCone->SetAwake (true); 
    pBodyPineCone->setPosition(position); 

    //update box2d 
    pBodyPineCone->SetTransform( 
      b2Vec2(position.x/PTM_RATIO, position.y/ PTM_RATIO), 
      _body->GetAngle()); 
} 


void updatePhysics() 
{ 
    _world->Step(.1, 10, 10); 
    for (b2Body *b = _world->GetBodyList(); b; b = b->GetNext()) 
    { 
     if (b->GetUserData() != NULL) 
     { 
      Sprite *ballData = dynamic_cast<Sprite*> ((Sprite *) b->GetUserData()); 
      ballData->setPosition(b->GetPosition().x * PTM_RATIO, 
           b->GetPosition().y * PTM_RATIO); 
      ballData->setRotation(-1 * CC_RADIANS_TO_DEGREES(b->GetAngle())); 
     } 
    } 
}