I need to pass glReadPixels a 2D array (well, it accepts a void*) to get the contents of the color buffer. It looked like vbl_array_2d would be helpful for this, but it is saying "could not convert vbl_array_2d to void* when I try to pass it. I don't see a vbl_array_2d::get_c_array() type of function - is there a way to do this?