Box2d SDL cannot apply world setting on a dynamic body - c++

Question

My dynamic body is not falling down after setting the world. It is not following the gravity. Even I apply force on the body it isn't work.
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);
}
}
I am not sure if I missed something in Main.
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()));
}
}
}