[cffi-devel] handling lisp to c arrays (and back) in CFFI (beginner questions)
Hello, Sorry for the long winded questions... I was wondering if someone could point me to any example example on how to set/get arrays in C from lisp ? I am using CFFI and Swig. currently I have only primitive interface functions that pass pointers and floats. I am thinking of three array cases. I'm a bit of a beginner here, so please bear with me - the existing documentation is not completely clear (to me, as a lisp beginner :-).. 1) the C function allocates an array (as a side effect) and passes back a pointer to array to lisp . I would later have to free memory for this array explicitly. 2) the lisp function allocates an array and passes a pointer to the "C" function, The C function modifies the array. In this case lisp would be allocating the array. Side question: Do I need to use CFFI in lisp to allocate the array ? - or can this be done transparently by the lisp dynamic typing when the array variable is bound ? 3) I have several simple C functions that return smaller arrays (like [ x, y, z], where x,y,z = float or integer.). Would be nice to be able to pass by value as a return value on the stack, but I am not sure how to handle this from C to lisp. Example: C function: Color getColorValue ( Image *image, x, y), Where color is a array triplet [r, g, b],, could be floats or ints depending... Desired lisp function: (let ((color (get-color-value image x y)) ; then do something with list "color 4) unrelated question...maybe this should be posted to swig list (but i am not sure if there are any active CFFI users in that group). Is there an easy way to automatically create lisp-style function names ? For example: swig generates: (cffi:defcfun ("frameHeight" frameHeight) :int (frame :pointer)) I would like to generate translate the C function name to "frame-height" (to make it more of a lisp style). I tried using %rename frameHeight frame-height in the swig. ".i" file template, but that doesn't seem to work. The notes in the documentation on "lispify" I am not at the stage where I understand it. I thought that some google searches would turn up some canonical examples or tutorials on this, but there are not many (except the curl example - and it makes me wonder how many people are actually using it :-) thanks again, K
You might want to take a look at GSD, http://repo.or.cz/w/gsd.git, in which I dealt with some of those issues. If you're on an implementation that supports static-vectors, you can allocate a foreign-array from lisp and have access to the same data in lisp through #'cl-array. Your getting/setting will happen with gref and (setf gref). If your application is non-numeric, you might need to add some code (GSD was written for numerical software, particularly GSLL, but should be general). However, I'm happy to accept patches. There is documentation, not entirely complete, that should get you started, but feel free to post on the gsll-devel mailing list, http://common-lisp.net/cgi-bin/mailman/listinfo/gsll-devel with questions. Liam On Thu, Jul 22, 2010 at 1:45 PM, Kevin Smith <k2msmith@gmail.com> wrote:
Hello, Sorry for the long winded questions... I was wondering if someone could point me to any example example on how to set/get arrays in C from lisp ? I am using CFFI and Swig. currently I have only primitive interface functions that pass pointers and floats. I am thinking of three array cases. I'm a bit of a beginner here, so please bear with me - the existing documentation is not completely clear (to me, as a lisp beginner :-)..
1) the C function allocates an array (as a side effect) and passes back a pointer to array to lisp . I would later have to free memory for this array explicitly. 2) the lisp function allocates an array and passes a pointer to the "C" function, The C function modifies the array. In this case lisp would be allocating the array. Side question: Do I need to use CFFI in lisp to allocate the array ? - or can this be done transparently by the lisp dynamic typing when the array variable is bound ? 3) I have several simple C functions that return smaller arrays (like [ x, y, z], where x,y,z = float or integer.). Would be nice to be able to pass by value as a return value on the stack, but I am not sure how to handle this from C to lisp. Example: C function: Color getColorValue ( Image *image, x, y), Where color is a array triplet [r, g, b],, could be floats or ints depending... Desired lisp function: (let ((color (get-color-value image x y)) ; then do something with list "color 4) unrelated question...maybe this should be posted to swig list (but i am not sure if there are any active CFFI users in that group). Is there an easy way to automatically create lisp-style function names ? For example: swig generates: (cffi:defcfun ("frameHeight" frameHeight) :int (frame :pointer)) I would like to generate translate the C function name to "frame-height" (to make it more of a lisp style). I tried using %rename frameHeight frame-height in the swig. ".i" file template, but that doesn't seem to work. The notes in the documentation on "lispify" I am not at the stage where I understand it. I thought that some google searches would turn up some canonical examples or tutorials on this, but there are not many (except the curl example - and it makes me wonder how many people are actually using it :-) thanks again, K
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participants (2)
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Kevin Smith -
Liam Healy