Re: glwDrawingAreaWidgetClass

[Chris Carlson <cwcarlsonc@cox.net>]

I apologize for being so vague.

I have a fairly large program that I developed on Fedora Linux.  It uses 
glwDrawingAreaClassRec to create a GL window.  I attempted to compile 
and run it on Cygwin, and I got the failure.

I added a print statement just before calling XtCreateManagedWidget() 
and discovered the value was 0 on Cygwin and an address on Linux.  I 
presumed that meant there was an issue.

To get around the problem, I downloaded the source from Mesa and 
compiled it myself.  The .a that was generated identifies the following 
(using nm):

0000000000000640 D glwDrawingAreaClassRec
0000000000000728 D glwDrawingAreaWidgetClass

I then compared it to /lib/libGLw.dll.a and got this:

nm /lib/libGLw.dll.a | grep DrawingAreaClass
0000000000000000 I __imp_glwMDrawingAreaClassRec
0000000000000000 I __nm_glwMDrawingAreaClassRec
0000000000000000 I __imp_glwDrawingAreaClassRec
0000000000000000 I __nm_glwDrawingAreaClassRec

Now I tried compiling your test program and found that it did work as 
you showed, but I then added the include of GLwDrawA.h, and it fails.  
This doesn't make a whole lot of sense to me, and it doesn't seem right.

What do you think?  If I want to use the GLwDrawingAreaWidgetClass, I 
would presume that I should include the corresponding header file and 
the class would be defined.

Thanks for your time, and I really do appreciate you and Cygwin.
Chris Carlson



On 10/7/2014 6:50 AM, Jon TURNEY wrote:
> On 07/10/2014 03:31, Chris Carlson wrote:
>> I've discovered that the constant glwDrawingAreaWidgetClass is set to
>> 0.  It's supposed to be defined as:
>>
>> WidgetClass 
>> glwDrawingAreaWidgetClass=(WidgetClass)&glwDrawingAreaClassRec;
>
> Can I ask you to please provide some more details as to how you made 
> this discovery?
>
> If you do this:
>
> $ cat glw-test.c
> #include <Xm/Xm.h>
> #include <GL/GLwDrawA.h>
> #include <stdio.h>
>
> int main()
> {
>    printf("glwDrawingAreaWidgetClass %p", glwDrawingAreaWidgetClass);
> }
>
> then you could reach that conclusion:
>
> $ gcc glw-test.c ; ./a
> glwDrawingAreaWidgetClass 0x0
>
> but this isn't testing correctly as glwDrawingAreaWidgetClass isn't 
> marked as extern in GLwDrawA.h
>
> $ cat glw-test.c
> #include <Xm/Xm.h>
> #include <stdio.h>
>
> extern WidgetClass glwDrawingAreaWidgetClass;
>
> int main()
> {
>    printf("glwDrawingAreaWidgetClass %p", glwDrawingAreaWidgetClass);
> }
>
> $ gcc glw-test.c -lGLw ; ./a
> glwDrawingAreaWidgetClass 0x5bd8e3640
>
>> Is it broken?
>
> I don't know.
>


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