[SDL] linux opengl extension

zed sexybastard at xtra.co.nz
Sat Jan 4 11:40:01 PST 2003


Nicolai Haehnle wrote:
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> 
> On Saturday 04 January 2003 05:38, zed wrote:
> 
>>ive been trying for a couple of weeks to get access to ALL opengl
>>extensions with SDL (with mixed results),
>>some word eg multitexture but some dont eg secondarycolor.
>>or pointparametersEXT works but pointparametersARB doesnt.
>>
>>does anyone have any idea what could possibly be happening?
>>i would appreciate if an expert would mail me with help (so i can
>>describe fully whats NOT happening)
>>
> 
> It would be helpful if you told us why/how it "doesn't work".
> 
> Are you sure the extensions actually exist? Check the GL_EXTENSIONS string 
> for that. A driver will only provide pointparametersEXT but not 
> pointparametersARB if it was written before pointparameters was promoted to 
> an ARB extension, for example.
> 
> Do you use SDL_GL_GetProcAddress() to get the extension functions?

yes to everything (note it works under windows)
heres another message i started about it.
http://www.opengl.org/discussion_boards/ubb/Forum4/HTML/000830.html

from an email from a nvidia developer
------------------------
One of our developers changed the behavior of the driver to avoid the
dynamic symbol resolution we are currently doing, but found that it didn't
actually fix your test.

What he found was that libsdl doesn't actually use the
GLX_ARB_get_proc_address extension.  Instead, it simply calls dlsym().
First it tries "glFunctionARB"; then it tries "_glFunctionARB" if it fails.
I don't know how Linux symbol naming works, but there seems to be something
weird going on.  dlsym has a flag RTLD_GLOBAL that makes symbols "global" so
they are returned even if they aren't in the named executable -- not sure if
symbols in your main executable would be global or not.  If they are,
perhaps they will be returned by any dlsym() call?  In any event, there may
be multiple symbols of any given name here.
------------------------

hes refering to this

void *X11_GL_GetProcAddress(_THIS, const char* proc)
{
         static char procname[1024];
         void* handle;
         void* retval;

         handle = this->gl_config.dll_handle;
#if 0 /* This doesn't work correctly yet */
         if ( this->gl_data->glXGetProcAddress ) {
...
...

also so why isnt this workinh yet #if 0 /* This doesn't work correctly 
yet */


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