[racket] Figured out the Mac OS X crashing issue for liballegro / libsdl / etc...

Hi Jon,


[Also CCing the Racket mailing list.  For folks who are writing
bindings to graphical libraries such as SDL, the following should be
relevant.]


When using the Allegro bindings on Mac OS X, the user will see an
exception on screen instantiation unless the program's running under a
Cocoa context.

Folks from other communities have figured out how to solve this.  In
particular, the PySDL folks have a small module to set it up.
(https://github.com/albertz/PySDL/blob/master/SDL/__init__.py)

I've ported the heart of this to Racket:

    https://gist.github.com/4526379

(Comment the use of initialize-ns-app in that code; I added it to make
sure it was getting called.)


initialize-ns-app provides a Cocoa context in which all the rest of
the graphical library usage must occur on Mac OS X.  So, typically
code will look like:

   ;; load foreign libraries...

   (initiaize-ns-app
      (lambda ()
         ;; Now it's safe to create the screen in here ...
      ))




If you don't do something like this, you'll see this exception as soon
as you start initializing the screen:

2013-01-13 15:07:22.716 racket[26263:707] *** Terminating app due to
uncaught exception 'NSInternalInconsistencyException', reason: 'Error
(1000) creating CGSWindow on line 259'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff8e6ca0a6
__exceptionPreprocess + 198
	1   libobjc.A.dylib                     0x00007fff9681e3f0
objc_exception_throw + 43
	2   CoreFoundation                      0x00007fff8e6c9e7c
+[NSException raise:format:] + 204
	3   AppKit                              0x00007fff951b2c29
_NSCreateWindowWithOpaqueShape2 + 655
	4   AppKit                              0x00007fff951b1420 -[NSWindow
_commonAwake] + 2002
	5   AppKit                              0x00007fff9516fe62 -[NSWindow
_commonInitFrame:styleMask:backing:defer:] + 1763
	6   AppKit                              0x00007fff9516efaf -[NSWindow
_initContent:styleMask:backing:defer:contentView:] + 1568
	7   AppKit                              0x00007fff9516e97f -[NSWindow
initWithContentRect:styleMask:backing:defer:] + 45
	8   SDL                                 0x0000000102f515cc
SDL_SoftStretch + 24672
	9   SDL                                 0x0000000102f4fe38
SDL_SoftStretch + 18636
	10  SDL                                 0x0000000102f44da1
SDL_SetVideoMode + 892
	11  Racket                              0x00000001002be82c ffi_call_unix64 + 76
	12  ???                                 0x00007fff5fbfd8d0 0x0 +
140734799796432
)
libc++abi.dylib: terminate called throwing an exception
Abort trap: 6