Stepping through the program when debugging, it (the Racket runtime) now crashes when running (cpArbiterGetShapes arb) with the modifications you suggested. (also I just pushed the changes to the GitHub repo for the bindings: https://github.com/Freezerburn/Rhipmunk-Physics if you want to take a look at them directly)
On Sun, Dec 2, 2012 at 8:23 PM, Ryan Culpepper <r...@cs.utah.edu> wrote: > Based on the documentation I found and the CP_ARBITER_GET_SHAPES macro, it > looks like the double-pointer arguments are just used for multiple outputs. > So you should use the following type for the function: > > (_fun _cpArbiter-pointer > (out1 : (_ptr o _cpShape-pointer)) > (out2 : (_ptr o _cpShape-pointer)) > -> _void > -> (values out1 out2)) > > The FFI takes care of allocating the necessary temporary space that the > function writes into. The Racket-side function takes just one argument (for > the arbiter), and it returns two _cpShape-pointer values. So you would use > it like this: > > (let-values ([(water poly) (cpArbiterGetShapes arb)]) > ___ > (let ([count (cpPolyShapeGetNumVerts poly)]) > ___)) > > Does that work? > > Ryan > > > > On 12/02/2012 07:59 PM, Vince Kuyatt wrote: >> >> So I recently started to poke at my humble little bindings to the >> Chipmunk library again. (someone sent me an email asking for help, >> which reminded me that I hadn't worked on it in a while) The problem >> is that I'm still stumbling over the same block that made me stop in >> the first place a number of months back. One of the function in the >> Chipmunk library (cpArbiterGetShapes) takes two double pointers to a >> cpShape. (cpShape**) So far, I have been unable to figure out how to >> make this work without a future function that accesses the cpShape >> crashing the entire Racket runtime, including the IDE window I have >> open. >> >> So the function definition for cpArbiterGetShapes is: >> static inline void cpArbiterGetShapes(const cpArbiter *arb, cpShape >> **a, cpShape **b) >> >> And my current binding in Racket is: >> (_fun _cpArbiter-pointer >> (_ptr io _cpShape-pointer) >> (_ptr io _cpShape-pointer) >> -> _void) >> >> And the (pertinent) code where I use it is: >> (let* >> ([water (cast (malloc _cpShape-pointer) _pointer _cpShape-pointer)] >> [poly (cast (malloc _cpShape-pointer) _pointer _cpShape-pointer)] >> [water-ptr (cast (malloc _cpShape-pointer) _pointer >> _cpShape-pointer)] >> [poly-ptr (cast (malloc _cpShape-pointer) _pointer >> _cpShape-pointer)]) >> (memcpy water-ptr water (ctype-sizeof _cpShape-pointer)) >> (memcpy poly-ptr poly (ctype-sizeof _cpShape-pointer)) >> (cpArbiterGetShapes arb water-ptr poly-ptr) >> (let* >> (... >> [count (cpPolyShapeGetNumVerts poly)] ;Note that it crashes >> on this line >> >> Which is following the buoyancy demo included in Chipmunk by default >> as close as possible. Also note that cpPolyShapeGetNumVerts is >> supposed to take a _cpShape-pointer. I'm really not sure how to do >> what I need in Racket given this situation, and all I've really seen >> in the Racket documentation is just single pointers. I've also tried >> just allocating water and poly with not water-ptr and poly-ptr and >> just using those, but that crashes Racket just the same. I would >> really, really, really appreciate any help with this. It's bugging me >> that I can't get this solved and I really want this to work. >> >> Thank you so much in advance for any assistance provided. (also I >> apologize if this ends up badly formatted. I'm not sure of formatting >> rules for a listserv when sending through email) >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> > ____________________ Racket Users list: http://lists.racket-lang.org/users
