[Chicken-users] c-callbacks

[Bastian Müller]

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Hi,

I'm currently trying to interface the Open Dynamics Engine and simple
simulations are working now. Next thing is to do collision detection.

ODE uses the following callback:
  typedef void dNearCallback (void *data, dGeomID o1, dGeomID o2);
that I interfaced by
  (define-foreign-type dNearCallback (function void (c-pointer  
dGeomID dGeomID)))

For the collision detection call
  void dSpaceCollide (dSpaceID space, void *data, dNearCallback  
*callback);
I used
  (define ode-space-collide
    (foreign-lambda void "dSpaceCollide" dSpaceID c-pointer  
dNearCallback))

As an example callback I defined:
  (define-external (foobar (c-pointer data) (dGeomID geom1) (dGeomID  
geom2)) void
    (printf "collision") (newline))

Finally, I tried to do the actual call.
First, I tried:
  (ode-space-collide space (null-pointer) foobar)
and during the simulation I got an
  Error: bad argument count - received -2 but expected 3: error in  
error
  graphics.scm: 76   ode-space-collide    <--

I looked into the expat egg, expat.scm, and saw it uses #$wrapper to
handle the callback, but
  (ode-space-collide space (null-pointer) #$foobar)
yields
  Error: (location) bad argument type - locative can not refer to
  objects of this type: #<procedure (foobar  data268 geom1269  
geom2270)>

  ##sys#make-locative                     <--

It would be great if someone could enlighten me, so I can get this
last part of the puzzle working and actually start on the game I'm
dreaming of. :-)

Thanks in advance,
your sincerely

- --
Bastian Müller - http://turbolent.com/


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