Re: [gl4java-usergroup] GLCanvas Dispose on NT

[<NM...@th...>]

Hi,

After doing some debugging I made the following change to my source.

In file : OpenGL_Win32_jawt.c
In the method : gljDestroyNative

We were trying to delete a context with : disp__wglDeleteContext(gc). An
error was occurring on my system (WinNT), I think, because the context
being deleted (gc) belonged to a thread other than the current thread and
thus threw an EXCEPTION_ACCESS_VIOLATION.
Previous to this (a few lines up from the above) we were calling  :
disp__wglMakeCurrent( NULL, NULL ) , which detaches the rendering context
from the current thread and makes it non-current, in preparation for
deletion. This call, however, was failing on my system. I am assuming it
was failing, again, because the current thread did not hold the rendering
context.

I am not exactly sure why the thread did not own the context. I must admit,
my experience with GL Windows programming is very limited. But here is what
I did to fix my error :

I changed disp__wglMakeCurrent( NULL, NULL ) to disp__wglMakeCurrent(
thisWin, gc ) so that the current thread now owns the context. Then, when
it gets around to deleting it a few lines later, no error occurs. According
to MSDN the disp__wglDeleteContext(gc) call will actually change the
rendering context to being non-current before deleting so really the
original disp__wglMakeCurrent( NULL, NULL ) was redundant. The only
important thing is to make sure that the current thread owns the context
before deleting it.

Is it a hack? I don't know. Thoughts? It has stopped my error though.

Thanks,
Noah Keen




|---------+--------------------------------------------->
|         |           "Kenneth B. Russell"              |
|         |           <kbr...@al...>           |
|         |           Sent by:                          |
|         |           gl4...@li...ur|
|         |           ceforge.net                       |
|         |                                             |
|         |                                             |
|         |           03/26/2002 12:03 AM               |
|         |           Please respond to kbrussel        |
|         |                                             |
|---------+--------------------------------------------->
  >----------------------------------------------------------------------------------------------|
  |                                                                                              |
  |       To:       NM...@th...                                                      |
  |       cc:       gl4...@li...                                      |
  |       Subject:  Re: [gl4java-usergroup] GLCanvas Dispose on NT                               |
  >----------------------------------------------------------------------------------------------|





> My application needs to swap a GLCanvas and a JPanel in and out of a GUI
> Container(JSplitPane). Currently I am destroying a GLCanvas with
cvsDispose
> () and then rebuilding by recalling the constructor with each swap.
>
> ...
>
> On a WinNT machine this call causes a EXCEPTION_ACCESS_VIOLATION outside
of
> the Java VM. It is happening in the gljDestroyNative() method in
> OpenGL_Win32_jawt.c when the native disp_wglDeleteContext(gc) call is
> made(Line 713).

There is pretty clearly something wrong in that code, as that
line is executing entirely inside a block guarded by "if (gc ==
0)".

Please spend some time and debug it if you can, then send in a
patch. Otherwise we'll look at it after JavaOne. BTW, Sven is in
San Francisco this week and he and I are giving a talk on OpenGL
for Java this Thursday morning at 11. If any of you are at the
conference we hope to see you there.

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