In the Draw call, I just render all buffered vertices collected from the dynamics world, at the entry point of Draw, it always reporting empty buffers. I have setup the DXDebugDrawer correctly by deriving from the btIDebugDraw interface and I've made a call to the setDebugDrawer, how come it didn't work?

if (m_dynamicsWorld)
{
m_dynamicsWorld->debugDrawWorld();
dynamic_cast(m_dynamicsWorld->getDebugDrawer())->Draw();
}