//C++ header - Open Scene Graph - Copyright (C) 1998-2002 Robert Osfield
//Distributed under the terms of the GNU Library General Public License (LGPL)
//as published by the Free Software Foundation.

#ifndef OSG_GLEXTENSIONS
#define OSG_GLEXTENSIONS 1

#include <osg/Export>

#if defined(WIN32)
#include <windows.h>
#elif defined(__DARWIN_OSX__)
#include <mach-o/dyld.h>
#else
#include <dlfcn.h>
#endif

namespace osg {

/** return true if OpenGL "extension" is supported.
  * note: Must only called within a valid OpenGL context,
  * undefined behavior may occur otherwise.
  */
SG_EXPORT extern const bool isGLExtensionSupported(const char *extension);

/** return the address of the specified OpenGL function.
  * return NULL if function not supported by OpenGL library.
  * Note, glGLExtensionFuncPtr is declared inline so that the code
  * is compiled localy to the calling code.  This should get by Windows
  * dumb implementation of having different GL function ptr's for each
  * library when links to it. 
  */
inline void* getGLExtensionFuncPtr(const char *funcName)
{
#if defined(WIN32)
    return wglGetProcAddress(funcName);
#elif defined(__DARWIN_OSX__)
    std::string temp( "_" );
    temp += funcName;	// Mac OS X prepends an underscore on function names
    if ( NSIsSymbolNameDefined( temp.c_str() ) )
    {
        NSSymbol symbol = NSLookupAndBindSymbol( temp.c_str() );
        return NSAddressOfSymbol( symbol );
    } else
	return NULL;
#else // all other unixes
   // Note: although we use shl_load() etc. for Plugins on HP-UX, it's
   // not neccessary here since we only used them because library
   // intialization was not taking place with dlopen() which renders
   // Plugins useless on HP-UX.
   static void *lib = dlopen("libGL.so", RTLD_LAZY);
   if (lib)
      return dlsym(lib, funcName);
   else
      return NULL;
#endif
}

/** return the address of the specified OpenGL function, if not found then
  * check a second function name, if this fails then return NULL as function is
  * not supported by OpenGL library.  This is usual for checking something
  * like glActiveTexture (which is in OGL1.3) or glActiveTextureARB.
  */
inline void* getGLExtensionFuncPtr(const char *funcName,const char *fallbackFuncName)
{
    void* ptr = getGLExtensionFuncPtr(funcName);
    if (ptr) return ptr;
    return getGLExtensionFuncPtr(fallbackFuncName);
}

}

#endif