Hi Jay, I know, I actually used your code and a fork of it on github as a starting point (https://github.com/Freezerburn/Rhipmunk-Physics). It really helped a lot! I have added your name to the authors list. If you have an issue with that I can remove it of course.
I'm going to use Matthew's solution just to make sure no pointers get messed up. Sam -----Oorspronkelijk bericht----- Van: Jay McCarthy [mailto:[email protected]] Verzonden: maandag 4 maart 2013 14:35 Aan: Sam Vervaeck CC: users Onderwerp: Re: [racket] FFI Pointing to racket objects I wrote an FFI for Chipmunk once: https://github.com/jeapostrophe/chipmunk/blob/master/chipmunk-ffi.ss I used _pointer rather than _racket for my body data. My understanding is that in your version, the Racket object is only available via the Chipmunk/C data structure, which the GC views as opaque, so it is collected. If you want to put Racket things in C objects, you'll have to make sure they are retained on the Racket side, by (for example), also storing them in a hash table and monitoring access to the C objects. Jay On Sat, Mar 2, 2013 at 8:35 AM, Sam Vervaeck <[email protected]> wrote: > Hi, > > > > I am forking an FFI library for physics simulation on Github > (https://github.com/samvv/Rhipmunk-Physics) but I got stuck with > storing racket objects in the library’s native structs. From the library’s > website: > http://chipmunk-physics.net/release/Chipmunk-6.x/Chipmunk-6.1.2-API-Reference/group__cp_body.html. > Here’s the part of the code that needs to be changed: > > > > (define _cpDataPointer _racket) > > (define-cstruct _cpBody > > … > > [data _cpDataPointer] ; user-defined data, like a game object > > …) > > > > In the following test everything seems to work as expected: > > > > (define body1 (cpBodyNew 1.0 1.0)) > > (set-cpBody-data! body1 "This is a test") > > (display (cpBody-data body1)) > >> “This is a test” > > (set-cpBody-data! body1 (cons 1 2)) > > (display (cpBody-data body1)) > >> (1 . 2) > > > > However, when I run the following code: > > > > (collect-garbage) > > (display (cpBody-data body1)) > > > > Something goes wrong internally. Sometimes DrRacket crashes, sometimes > it returns values like #<bad-value>. I have looked into > (malloc-immobile-cell > v) and (free-immobile-cell cptr) but I am not sure that fiddling with > the memory is such a good idea. Could you please give me any > guidelines or point me to a procedure I can use to provide this functionality? > > > > Thanks, > > > > Sam > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > -- Jay McCarthy <[email protected]> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 ____________________ Racket Users list: http://lists.racket-lang.org/users
