Help wrapping this struct?

[Joeish W]

not sure of the wording on this so pls bear with me

in OpenCV  when you want to create an image you do this 

IplImage* img=cvCreateImage(cvGetSize(imgHSV),IPL_DEPTH_8U, 1);

or you can do this 

img=cvCreateImage(cvGetSize(imgHSV),IPL_DEPTH_8U, 1);

if you've already called the below first 



IplImage* img;

my question is...since i already wrapped cvCreateImage

with this successfully


;; IplImage* cvCreateImage(CvSize size, int depth, int channels)
(cffi:defcfun ("cvCreateImage" %create-image) (:pointer (:struct ipl-image))
  (size :int64)
  (depth :int)
  (channels :int))

(defun create-image (size depth channels)
  "Create an image with dimensions given by SIZE, DEPTH bits per
channel, and CHANNELS number of channels."
  (let ((nsize (size->int64 size)))
    (%create-image nsize depth channels)))


and i use it all the time successfully,  converting c opencv code into lisp in many programs...and have never once did this

IplImage* img;

I always call it in a let like this

(img (create-image sz +ipl-depth-8u+ 3))


but if i wanted to expose this kind of functionality in lisp where i would  call i/e

(ipl-image img) first before calling(img (create-image sz +ipl-depth-8u+ 3)) how would i do that
I tried writing a glue wrapper in c

IplImage* IplImage_glue(int img)
{
    return (IplImage *) img; 
}

here is my repl history after that was compiled into a .so(ubuntu raring)

CL-OPENCV> ;; IplImage* IplImage_glue(IplImage* img);
(cffi:defcfun ("IplImage_glue" ipl-image) (:pointer (:struct ipl-image))
  (img (:pointer (:struct ipl-image))))

IPL-IMAGE
CL-OPENCV> (dp img (cffi:null-pointer))
IMG
CL-OPENCV> (ipl-image img)
#.(SB-SYS:INT-SAP #X00000000)
CL-OPENCV>  (cffi:with-foreign-slots ((n-size) 
img (:struct ipl-image)) 
(format t 
"n-size = ~a~%"
 n-size))

every thing runs up until the with-foreign-slots then..
Unhandled memory fault at #x0.
   [Condition of type SB-SYS:MEMORY-FAULT-ERROR]




..i assume because im not accessing a ipl-image struct pointer but maybe i am.....any help is appreciated
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