void readPixelsNormal()
{
  // init mem
  unsigned int * m_pBufferColor = new unsigned int[GetWidth() * GetHeight()]; 
  unsigned int * m_pBufferDepth = new unsigned int[GetWidth() * GetHeight()];

  glReadPixels(0, 0, GetWidth(), GetHeight(), GL_RGBA, GL_UNSIGNED_BYTE, 
               m_pBufferColor);
  //... do stuff to the pixels ...

  glReadPixels(0, 0, GetWidth(), GetHeight(), GL_DEPTH_COMPONENT,
               GL_UNSIGNED_INT, m_pBufferDepth);
  //... do stuff to the pixels ...
}

// macro for pointing glReadPixels to ... well ... nowhere
#define BUFFER_OFFSET(i) ((char *)NULL + (i))

// PBO generated IDs
GLuint m_pPBO[2] = {0, 0};
unsigned int * m_pBuffer;

void initPBO()
{
  // init the PBOs
  glGenBuffersARB(2, m_pPBO);
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, m_pPBO[0]);
  glBufferDataARB(GL_PIXEL_PACK_BUFFER_EXT, 
                  (GetWidth() * GetHeight() * sizeof(unsigned int)), 
                  NULL, 
                  GL_STREAM_READ);

  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, m_pPBO[1]);
  glBufferDataARB(GL_PIXEL_PACK_BUFFER_EXT, 
                  (GetWidth() * GetHeight() * sizeof(unsigned int)), 
                  NULL, 
                  GL_STREAM_READ);
  
  // bind it to nothing so other stuff doesn't
  // think it should use the PBOs
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, 0);
}

void readPixelsPBO()
{
  // bind buffer #1
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, m_pPBO[0]);

  // read pixels
  glReadPixels(0, 0, GetWidth(), GetHeight(), GL_RGBA,
               GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));

  // map memory from card
  m_pBuffer = static_cast<unsigned int *>(glMapBufferARB(GL_PIXEL_PACK_BUFFER_EXT, GL_READ_ONLY_ARB));

  //... do stuff to pixels ...
  
  // unmap the memory
  if (!glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_EXT))
  {
    //  handle the error
  }

  // bind buffer #2
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, m_pPBO[1]);

  // read pixels
  glReadPixels(0, 0, GetWidth(), GetHeight(), GL_RGBA,
               GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));

  // map memory from card
  m_pBuffer = static_cast<unsigned int *>(glMapBufferARB(GL_PIXEL_PACK_BUFFER_EXT, GL_READ_ONLY_ARB));

  //... do stuff to pixels ...

  // unmap the memory
  if (!glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_EXT))
  {
    //  handle the error
  }

  // bind it to nothing so other stuff doesn't
  // think it should use the PBOs
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, 0);
}

void killPBO()
{
  // kill the PBOs
  glDeleteBuffersARB(2, m_pPBO);
  glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, 0);  
}