Debugging a Callback

[James Ashley]

This may not be the proper list (I'm tempted to cross-post to the clozure
one), but I have to start somewhere.

I'm putting together a wrapper around the recently released version of the
C library GLFW. In the middle of a callback (written in CL and mostly using
cl-glfw), I'm winding up in the debugger, and I'm not having any luck
figuring out why.

I don't have a minimal test-case to share, yet. That's my next step. I'm
being lazy and asking before I start trying to trim pieces down. The best
nutshell of the problem I have at the moment is that the callback in
question looks like:

(cffi:defcallback window-sizer
    :void
  ((window glfw3::glfw-window) (width :int) (height :int))
  ;; Have to have the OpenGL context before we can do this.
  ;; Q: Should I be making that window's context current?
  ;; A: Seems really stupid to think otherwise.
  (declare (ignore window))
  (format t "Resizing to ~A x ~A~%" width height)
  (gl:viewport 0 0 width height)
  (format t "Setting projecting matrix~%")
  (gl:matrix-mode :projection)
  (gl:load-identity)
  (let ((ratio (/ width height)))
    (format t "Setting ortho: ~A~%" ratio)
    ;; This next line is failing here, pretty spectacularly.
    ;; with an error message that doesn't seem to make any sense.
    ;; It appears to run fine (even if it does nothing) when
    ;; I run it throuh the REPL.
    (gl:ortho (- ratio) ratio -1 1 1 -1))
  (format t "Returning~%"))

The stack trace (FWIW) looks like:
The value 17465867632912 is not of the expected type DOUBLE-FLOAT.
   [Condition of type TYPE-ERROR]

  0: (CFFI-CALLBACKS::|GLFW3-EXAMPLE::WINDOW-SIZER| 17465867632956)
      Locals:
        #:G7819 = 17465867632956
        #:G7822 = #<A Foreign Pointer [stack-allocated] #x7F14B6B009E0>
        GLFW3-EXAMPLE::WINDOW = #<A Foreign Pointer #x7F149C034C70>
        GLFW3-EXAMPLE::WIDTH = 649
        GLFW3-EXAMPLE::HEIGHT = 502
        COMMON-LISP:RATIO = 649/502
        CL-OPENGL-BINDINGS::LEFT = -649/502
        #:G7833 = -1.292828685258964D0
        #:G7834 = 1.292828685258964D0
        #:G7835 = -1.0D0
        #:G7836 = 1.0D0
        #:G7837 = 1.0D0
        #:G7838 = -1.0D0
  1: (CCL::%PASCAL-FUNCTIONS% 5 17465867632956)
      Locals:
        INDEX = 5
        ARGS-PTR-FIXNUM = 17465867632956
        LISP-FUNCTION = #<Compiled-function
CFFI-CALLBACKS::|GLFW3-EXAMPLE::WINDOW-SIZER| (Non-Global)  #x302001CF9B0F>
        WITHOUT-INTERRUPTS = NIL
        *CALLBACK-TRACE-P* = NIL
  2: (NIL #<Unknown Arguments>)
  3: (POLL-EVENTS)
  4: (CCL::CALL-CHECK-REGS POLL-EVENTS)
  5: (CCL::CHEAP-EVAL (POLL-EVENTS))

Does anyone have a suggestion about where I should look to try to figure
out where that value it's complaining about comes from? Or what's expecting
the DOUBLE-FLOAT? Is there something else in the stack trace (or anywhere
else) that I'm just totally missing due to my noobishness?

The C signature of the callback function is
typedef void (* GLFWwindowsizefun)(GLFWwindow*,int,int);

Is there something else I can supply that I didn't realize is important?

Just for the record, I'm much more interested in learning how I can
diagnose and fix these sorts of problems for myself than anything else. I
just seemed to run into a total dead end on google.

Thanks in advance,
James
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