Help wrapping a opencv c struct

Discussion of Common Lisp

Help wrapping a opencv c struct

Postby joeish80829 » Tue Oct 15, 2013 1:23 pm

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);
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or you can do this

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

if you've already called the below first

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IplImage* img;

my question is...since i already wrapped cvCreateImage

with this successfully

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;; 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

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IplImage* img;

I always call it in a let like this

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(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

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(ipl-image img)
first before calling
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 (img (create-image sz +ipl-depth-8u+ 3))
how would i do that

I tried writing a glue wrapper in c

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

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

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

CL-OPENCV> (dp img (cffi:null-pointer))
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~%"

every thing runs up until the with-foreign-slots then..

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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
Posts: 153
Joined: Tue Sep 03, 2013 5:32 am

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