/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
 *
 * This library is open source and may be redistributed and/or modified under
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * OpenSceneGraph Public License for more details.
*/
#include <osg/GLExtensions>
#include <osg/GL>
#include <osg/Notify>
#include <osg/Math>
#include <osg/buffered_value>

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <float.h>

#include <string>
#include <set>
#include <sstream>

#if defined(WIN32)
    #ifndef WIN32_LEAN_AND_MEAN
        #define WIN32_LEAN_AND_MEAN
    #endif // WIN32_LEAN_AND_MEAN
    #ifndef NOMINMAX
        #define NOMINMAX
    #endif // NOMINMAX
    #include <windows.h>
#elif defined(__APPLE__)
    // The NS*Symbol* stuff found in <mach-o/dyld.h> is deprecated.
    // Since 10.3 (Panther) OS X has provided the dlopen/dlsym/dlclose
    // family of functions under <dlfcn.h>. Since 10.4 (Tiger), Apple claimed
    // the dlfcn family was significantly faster than the NS*Symbol* family.
    // Since 'deprecated' needs to be taken very seriously with the
    // coming of 10.5 (Leopard), it makes sense to use the dlfcn family when possible.
    #include <AvailabilityMacros.h>
    #if !defined(MAC_OS_X_VERSION_10_3) || (MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_3)
        #define USE_APPLE_LEGACY_NSSYMBOL
        #include <mach-o/dyld.h>
    #else
        #include <dlfcn.h>
    #endif
#elif defined(__EMSCRIPTEN__)
    // Emscripten ships EGL, which we use to get OpenGL function addresses.
    #include <EGL/egl.h>
#else
    #include <dlfcn.h>
#endif

using namespace osg;

typedef std::set<std::string>  ExtensionSet;
static osg::buffered_object<ExtensionSet> s_glExtensionSetList;
static osg::buffered_object<std::string> s_glRendererList;
static osg::buffered_value<int> s_glInitializedList;

static osg::buffered_object<ExtensionSet> s_gluExtensionSetList;
static osg::buffered_object<std::string> s_gluRendererList;
static osg::buffered_value<int> s_gluInitializedList;

float osg::getGLVersionNumber()
{
    // needs to be extended to do proper things with subversions like 1.5.1, etc.
    char *versionstring   = (char*) glGetString( GL_VERSION );
    if (!versionstring) return 0.0;

    return (findAsciiToFloat(versionstring));
}

bool osg::isExtensionInExtensionString(const char *extension, const char *extensionString)
{
    const char *startOfWord = extensionString;
    const char *endOfWord;
    while ((endOfWord = strchr(startOfWord,' ')) != 0)
    {
        if (strncmp(extension, startOfWord, endOfWord - startOfWord) == 0)
            return true;
        startOfWord = endOfWord+1;
    }
    if (*startOfWord && strcmp(extension, startOfWord) == 0)
        return true;

   return false;
}

bool osg::isGLExtensionSupported(unsigned int contextID, const char *extension)
{
    return osg::isGLExtensionOrVersionSupported(contextID, extension, FLT_MAX);
}

bool osg::isGLExtensionSupported(unsigned int contextID, const char *extension1, const char *extension2)
{
    return osg::isGLExtensionOrVersionSupported(contextID, extension1, FLT_MAX) ||
           osg::isGLExtensionOrVersionSupported(contextID, extension2, FLT_MAX);
}

bool osg::isGLExtensionOrVersionSupported(unsigned int contextID, const char *extension, float requiredGLVersion)
{
    ExtensionSet& extensionSet = s_glExtensionSetList[contextID];
    std::string& rendererString = s_glRendererList[contextID];

    // first check to see if GL version number of recent enough.
    bool result = requiredGLVersion <= osg::getGLVersionNumber();

    if (!result)
    {
        // if not already set up, initialize all the per graphic context values.
        if (!s_glInitializedList[contextID])
        {
            s_glInitializedList[contextID] = 1;

            // set up the renderer
            const GLubyte* renderer = glGetString(GL_RENDERER);
            rendererString = renderer ? (const char*)renderer : "";

            // get the extension list from OpenGL.
            GLint numExt = 0;
            #if !defined(OSG_GLES1_AVAILABLE) && !defined(OSG_GLES2_AVAILABLE)
            if( osg::getGLVersionNumber() >= 3.0 )
            {
                // OpenGL 3.0 adds the concept of indexed strings and
                // deprecates calls to glGetString( GL_EXTENSIONS ), which
                // will now generate GL_INVALID_ENUM.

                // Get extensions using new indexed string interface.

                typedef const GLubyte * GL_APIENTRY MYGLGETSTRINGIPROC( GLenum, GLuint );
                MYGLGETSTRINGIPROC* glGetStringi = 0;
                setGLExtensionFuncPtr( glGetStringi, "glGetStringi", true);

                if( glGetStringi != NULL )
                {
                    #  ifndef GL_NUM_EXTENSIONS
                    #    define GL_NUM_EXTENSIONS 0x821D
                    #  endif
                    glGetIntegerv( GL_NUM_EXTENSIONS, &numExt );
                    int idx;
                    for( idx=0; idx<numExt; idx++ )
                    {
                        extensionSet.insert( std::string( (char*)( glGetStringi( GL_EXTENSIONS, idx ) ) ) );
                    }
                }
                else
                {
                    OSG_WARN << "isGLExtensionOrVersionSupported: Can't obtain glGetStringi function pointer." << std::endl;
                }
            }
            #endif

            // No extensions found so far, so try with glGetString
            if (numExt == 0)
            {
                // Get extensions using GL1/2 interface.

                const char* extensions = (const char*)glGetString(GL_EXTENSIONS);
                if (extensions==NULL) return false;

                // insert the ' ' delimiated extensions words into the extensionSet.
                const char *startOfWord = extensions;
                const char *endOfWord;
                while ((endOfWord = strchr(startOfWord,' '))!=NULL)
                {
                    extensionSet.insert(std::string(startOfWord,endOfWord));
                    startOfWord = endOfWord+1;
                }
                if (*startOfWord!=0) extensionSet.insert(std::string(startOfWord));
            }

    #if defined(WIN32) && (defined(OSG_GL1_AVAILABLE) || defined(OSG_GL2_AVAILABLE) || defined(OSG_GL3_AVAILABLE))

            // add WGL extensions to the list

            typedef const char* WINAPI WGLGETEXTENSIONSSTRINGARB(HDC);
            WGLGETEXTENSIONSSTRINGARB* wglGetExtensionsStringARB = 0;
            setGLExtensionFuncPtr(wglGetExtensionsStringARB, "wglGetExtensionsStringARB");

            typedef const char* WINAPI WGLGETEXTENSIONSSTRINGEXT();
            WGLGETEXTENSIONSSTRINGEXT* wglGetExtensionsStringEXT = 0;
            setGLExtensionFuncPtr(wglGetExtensionsStringEXT, "wglGetExtensionsStringEXT");

            const char* wglextensions = 0;

            if (wglGetExtensionsStringARB)
            {
                HDC dc = wglGetCurrentDC();
                wglextensions = wglGetExtensionsStringARB(dc);
            }
            else if (wglGetExtensionsStringEXT)
            {
                wglextensions = wglGetExtensionsStringEXT();
            }

            if (wglextensions)
            {
                const char* startOfWord = wglextensions;
                const char* endOfWord;
                while ((endOfWord = strchr(startOfWord, ' ')))
                {
                    extensionSet.insert(std::string(startOfWord, endOfWord));
                    startOfWord = endOfWord+1;
                }
                if (*startOfWord != 0) extensionSet.insert(std::string(startOfWord));
            }

    #endif

            OSG_NOTIFY(INFO)<<"OpenGL extensions supported by installed OpenGL drivers are:"<<std::endl;
            for(ExtensionSet::iterator itr=extensionSet.begin();
                itr!=extensionSet.end();
                ++itr)
            {
                OSG_NOTIFY(INFO)<<"    "<<*itr<<std::endl;
            }

        }

        // true if extension found in extensionSet.
        result = extensionSet.find(extension)!=extensionSet.end();
    }

    // now see if extension is in the extension disabled list
    bool extensionDisabled = false;
    if (result)
    {

        const std::string& disableString = getGLExtensionDisableString();
        if (!disableString.empty())
        {

            std::string::size_type pos=0;
            while ( pos!=std::string::npos && (pos=disableString.find(extension,pos))!=std::string::npos )
            {
                std::string::size_type previousColon = disableString.find_last_of(':',pos);
                std::string::size_type previousSemiColon = disableString.find_last_of(';',pos);

                std::string renderer = "";
                if (previousColon!=std::string::npos)
                {
                    if (previousSemiColon==std::string::npos) renderer = disableString.substr(0,previousColon);
                    else if (previousSemiColon<previousColon) renderer = disableString.substr(previousSemiColon+1,previousColon-previousSemiColon-1);
                }

                if (!renderer.empty())
                {

                    // remove leading spaces if they exist.
                    std::string::size_type leadingSpaces = renderer.find_first_not_of(' ');
                    if (leadingSpaces==std::string::npos) renderer = ""; // nothing but spaces
                    else if (leadingSpaces!=0) renderer.erase(0,leadingSpaces);

                    // remove trailing spaces if they exist.
                    std::string::size_type trailingSpaces = renderer.find_last_not_of(' ');
                    if (trailingSpaces!=std::string::npos) renderer.erase(trailingSpaces+1,std::string::npos);

                }

                if (renderer.empty())
                {
                    extensionDisabled = true;
                    break;
                }

                if (rendererString.find(renderer)!=std::string::npos)
                {
                    extensionDisabled = true;
                    break;

                }

                // move the position in the disable string along so that the same extension is found multiple times
                ++pos;
            }

        }
    }

    if (result)
    {
        if (!extensionDisabled)
        {
            OSG_NOTIFY(INFO)<<"OpenGL extension '"<<extension<<"' is supported."<<std::endl;
        }
        else
        {
            OSG_NOTIFY(INFO)<<"OpenGL extension '"<<extension<<"' is supported by OpenGL\ndriver but has been disabled by osg::getGLExtensionDisableString()."<<std::endl;
        }
    }
    else
    {
        OSG_NOTIFY(INFO)<<"OpenGL extension '"<<extension<<"' is not supported."<<std::endl;
    }


    return result && !extensionDisabled;
}

void osg::setGLExtensionDisableString(const std::string& disableString)
{
    getGLExtensionDisableString() = disableString;
}

std::string& osg::getGLExtensionDisableString()
{
    static const char* envVar = getenv("OSG_GL_EXTENSION_DISABLE");
    static std::string s_GLExtensionDisableString(envVar?envVar:"Nothing defined");

    return s_GLExtensionDisableString;
}

OSG_INIT_SINGLETON_PROXY(GLExtensionDisableStringInitializationProxy, osg::getGLExtensionDisableString())

#ifdef OSG_GL_LIBRARY_STATIC

    #include "GLStaticLibrary.h"

    void* osg::getGLExtensionFuncPtr(const char *funcName)
    {
        return GLStaticLibrary::getProcAddress(funcName);
    }

#else

    void* osg::getGLExtensionFuncPtr(const char *funcName)
    {
        // OSG_NOTICE<<"osg::getGLExtensionFuncPtr("<<funcName<<")"<<std::endl;
    #if defined(__ANDROID__)
        #if defined(OSG_GLES1_AVAILABLE)
            static void *handle = dlopen("libGLESv1_CM.so", RTLD_NOW);
        #elif defined(OSG_GLES2_AVAILABLE)
            static void *handle = dlopen("libGLESv2.so", RTLD_NOW);
        #endif
        return dlsym(handle, funcName);

    #elif defined(WIN32)

        #if defined(OSG_GLES2_AVAILABLE)
            static HMODULE hmodule = GetModuleHandle(TEXT("libGLESv2.dll"));
            return convertPointerType<void*, PROC>(GetProcAddress(hmodule, funcName));
        #elif defined(OSG_GLES1_AVAILABLE)
            static HMODULE hmodule = GetModuleHandleA(TEXT("libgles_cm.dll"));
            return convertPointerType<void*, PROC>(GetProcAddress(hmodule, funcName));
        #else
            return convertPointerType<void*, PROC>(wglGetProcAddress(funcName));
        #endif

    #elif defined(__APPLE__)

        #if defined(USE_APPLE_LEGACY_NSSYMBOL)
            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
            // I am uncertain of the correct and ideal usage of dlsym here.
            // On the surface, it would seem that the FreeBSD implementation
            // would be the ideal one to copy, but ELF and Mach-o are different
            // and Apple's man page says the following about using RTLD_DEFAULT:
            // "This can be a costly search and should be avoided."
            // The documentation mentions nothing about passing in 0 so I must
            // assume the behavior is undefined.
            // So I could try copying the Sun method which I think all this
            // actually originated from.

            // return dlsym( RTLD_DEFAULT, funcName );
            static void *handle = dlopen((const char *)0L, RTLD_LAZY);
            return dlsym(handle, funcName);
        #endif

    #elif defined (__sun)

        static void *handle = dlopen((const char *)0L, RTLD_LAZY);
        return dlsym(handle, funcName);

    #elif defined (__sgi)

        static void *handle = dlopen((const char *)0L, RTLD_LAZY);
        return dlsym(handle, funcName);

    #elif defined (__FreeBSD__)

        return dlsym( RTLD_DEFAULT, funcName );

    #elif defined (__linux__)

        typedef void (*__GLXextFuncPtr)(void);
        typedef __GLXextFuncPtr (*GetProcAddressARBProc)(const char*);

        #if !defined(OSG_GLES1_AVAILABLE) && !defined(OSG_GLES2_AVAILABLE)
        static GetProcAddressARBProc s_glXGetProcAddressARB = convertPointerType<GetProcAddressARBProc, void*>(dlsym(0, "glXGetProcAddressARB"));
        if (s_glXGetProcAddressARB)
        {
            return convertPointerType<void*, __GLXextFuncPtr>((s_glXGetProcAddressARB)(funcName));
        }
        #endif

        return dlsym(0, funcName);

    #elif defined (__QNX__)

        return dlsym(RTLD_DEFAULT, funcName);

    #elif defined(__EMSCRIPTEN__)
        // Use EGL to get OpenGL function address for Emscripten.
        return convertPointerType<void*, __eglMustCastToProperFunctionPointerType>(eglGetProcAddress(funcName));

    #else // all other unixes

        return dlsym(0, funcName);

    #endif
    }
#endif

///////////////////////////////////////////////////////////////////////////
// Static array of percontext osg::GLExtensions instances

typedef osg::buffered_object< osg::ref_ptr<GLExtensions> > BufferedExtensions;
static BufferedExtensions s_extensions;

GLExtensions* GLExtensions::Get(unsigned int in_contextID, bool createIfNotInitalized)
{
    if (!s_extensions[in_contextID] && createIfNotInitalized)
            s_extensions[in_contextID] = new GLExtensions(in_contextID);

    return s_extensions[in_contextID].get();
}

void GLExtensions::Set(unsigned int in_contextID, GLExtensions* extensions)
{
    s_extensions[in_contextID] = extensions;
}

///////////////////////////////////////////////////////////////////////////
// Extension function pointers for OpenGL v2.x


GLExtensions::GLExtensions(unsigned int in_contextID):
    contextID(in_contextID)
{
    const char* versionString = (const char*) glGetString( GL_VERSION );
    bool validContext = versionString!=0;
    if (!validContext)
    {
        OSG_NOTIFY(osg::FATAL)<<"Error: OpenGL version test failed, requires valid graphics context."<<std::endl;
    }

    glVersion = validContext ? findAsciiToFloat( versionString ) : 0.0f;
    glslLanguageVersion = 0.0f;

    bool shadersBuiltIn = OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES;

    isShaderObjectsSupported = validContext && (shadersBuiltIn || osg::isGLExtensionSupported(contextID,"GL_ARB_shader_objects"));
    isVertexShaderSupported = validContext && (shadersBuiltIn || osg::isGLExtensionSupported(contextID,"GL_ARB_vertex_shader"));
    isFragmentShaderSupported = validContext && (shadersBuiltIn || osg::isGLExtensionSupported(contextID,"GL_ARB_fragment_shader"));
    isLanguage100Supported = validContext && (shadersBuiltIn || osg::isGLExtensionSupported(contextID,"GL_ARB_shading_language_100"));
    isGeometryShader4Supported = validContext && (osg::isGLExtensionSupported(contextID,"GL_EXT_geometry_shader4") || osg::isGLExtensionSupported(contextID,"GL_OES_geometry_shader"));
    isGpuShader4Supported = validContext && osg::isGLExtensionSupported(contextID,"GL_EXT_gpu_shader4");
    areTessellationShadersSupported = validContext && (osg::isGLExtensionSupported(contextID, "GL_ARB_tessellation_shader") || osg::isGLExtensionSupported(contextID,"GL_OES_tessellation_shader"));
    isUniformBufferObjectSupported = validContext && osg::isGLExtensionSupported(contextID,"GL_ARB_uniform_buffer_object");
    isGetProgramBinarySupported = validContext && osg::isGLExtensionSupported(contextID,"GL_ARB_get_program_binary");
    isGpuShaderFp64Supported = validContext && osg::isGLExtensionSupported(contextID,"GL_ARB_gpu_shader_fp64");
    isShaderAtomicCountersSupported = validContext && osg::isGLExtensionSupported(contextID,"GL_ARB_shader_atomic_counters");

    isRectangleSupported = validContext &&
                           (OSG_GL3_FEATURES ||
                           isGLExtensionSupported(contextID,"GL_ARB_texture_rectangle") ||
                           isGLExtensionSupported(contextID,"GL_EXT_texture_rectangle") ||
                           isGLExtensionSupported(contextID,"GL_NV_texture_rectangle"));

    isCubeMapSupported = validContext &&
                          (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES ||
                          isGLExtensionSupported(contextID,"GL_ARB_texture_cube_map") ||
                          isGLExtensionSupported(contextID,"GL_EXT_texture_cube_map") ||
                          (glVersion >= 1.3f));

    isClipControlSupported = validContext &&
                             (isGLExtensionSupported(contextID,"GL_ARB_clip_control") ||
                             (glVersion >= 4.5f));


    isGlslSupported = validContext &&
                      (( glVersion >= 2.0f ) ||
                       (isShaderObjectsSupported &&
                        isVertexShaderSupported &&
                        isFragmentShaderSupported &&
                        isLanguage100Supported ));

    if( isGlslSupported )
    {
        // If glGetString raises an error, assume initial release "1.00"
        while(glGetError() != GL_NO_ERROR) {}        // reset error flag

        const char* langVerStr = (const char*)glGetString(GL_SHADING_LANGUAGE_VERSION);
        if( (glGetError() == GL_NO_ERROR) && langVerStr )
        {
            glslLanguageVersion = (findAsciiToFloat(langVerStr));
        }
        else
            glslLanguageVersion = 1.0f;
    }

    OSG_INFO
            << "glVersion=" << glVersion << ", "
            << "isGlslSupported=" << (isGlslSupported ? "YES" : "NO") << ", "
            << "glslLanguageVersion=" << glslLanguageVersion
            << std::endl;


    setGLExtensionFuncPtr(glDrawBuffers, "glDrawBuffers", "glDrawBuffersARB", validContext);
    setGLExtensionFuncPtr(glAttachShader, "glAttachShader", "glAttachObjectARB", validContext);
    setGLExtensionFuncPtr(glBindAttribLocation, "glBindAttribLocation", "glBindAttribLocationARB", validContext);
    setGLExtensionFuncPtr(glCompileShader, "glCompileShader", "glCompileShaderARB", validContext);
    setGLExtensionFuncPtr(glCreateProgram, "glCreateProgram", "glCreateProgramObjectARB", validContext);
    setGLExtensionFuncPtr(glCreateShader, "glCreateShader", "glCreateShaderObjectARB", validContext);
    setGLExtensionFuncPtr(glDeleteProgram, "glDeleteProgram", validContext);
    setGLExtensionFuncPtr(glDeleteShader, "glDeleteShader", validContext);
    setGLExtensionFuncPtr(glDetachShader, "glDetachShader", "glDetachObjectARB", validContext);
    setGLExtensionFuncPtr(glDisableVertexAttribArray, "glDisableVertexAttribArray", validContext);
    setGLExtensionFuncPtr(glEnableVertexAttribArray, "glEnableVertexAttribArray", validContext);
    setGLExtensionFuncPtr(glGetActiveAttrib, "glGetActiveAttrib", "glGetActiveAttribARB", validContext);
    setGLExtensionFuncPtr(glGetActiveUniform, "glGetActiveUniform", "glGetActiveUniformARB", validContext);
    setGLExtensionFuncPtr(glGetAttachedShaders, "glGetAttachedShaders", "glGetAttachedObjectsARB", validContext);
    setGLExtensionFuncPtr(glGetAttribLocation, "glGetAttribLocation", "glGetAttribLocationARB", validContext);
    setGLExtensionFuncPtr(glGetProgramiv, "glGetProgramiv", validContext);
    setGLExtensionFuncPtr(glGetProgramInfoLog, "glGetProgramInfoLog", validContext);
    setGLExtensionFuncPtr(glGetShaderiv, "glGetShaderiv", validContext);
    setGLExtensionFuncPtr(glGetShaderInfoLog, "glGetShaderInfoLog", validContext);
    setGLExtensionFuncPtr(glGetShaderSource, "glGetShaderSource", "glGetShaderSourceARB", validContext);
    setGLExtensionFuncPtr(glGetUniformLocation, "glGetUniformLocation", "glGetUniformLocationARB", validContext);
    setGLExtensionFuncPtr(glGetUniformfv, "glGetUniformfv", "glGetUniformfvARB", validContext);
    setGLExtensionFuncPtr(glGetUniformiv, "glGetUniformiv", "glGetUniformivARB", validContext);
    setGLExtensionFuncPtr(glGetVertexAttribdv, "glGetVertexAttribdv", validContext);
    setGLExtensionFuncPtr(glGetVertexAttribfv, "glGetVertexAttribfv", validContext);
    setGLExtensionFuncPtr(glGetVertexAttribiv, "glGetVertexAttribiv", validContext);
    setGLExtensionFuncPtr(glGetVertexAttribPointerv, "glGetVertexAttribPointerv", validContext);
    setGLExtensionFuncPtr(glIsProgram, "glIsProgram", validContext);
    setGLExtensionFuncPtr(glIsShader, "glIsShader", validContext);
    setGLExtensionFuncPtr(glLinkProgram, "glLinkProgram", "glLinkProgramARB", validContext);
    setGLExtensionFuncPtr(glShaderSource, "glShaderSource", "glShaderSourceARB", validContext);
    setGLExtensionFuncPtr(glUseProgram, "glUseProgram", "glUseProgramObjectARB", validContext);
    setGLExtensionFuncPtr(glUniform1f, "glUniform1f", "glUniform1fARB", validContext);
    setGLExtensionFuncPtr(glUniform2f, "glUniform2f", "glUniform2fARB", validContext);
    setGLExtensionFuncPtr(glUniform3f, "glUniform3f", "glUniform3fARB", validContext);
    setGLExtensionFuncPtr(glUniform4f, "glUniform4f", "glUniform4fARB", validContext);
    setGLExtensionFuncPtr(glUniform1i, "glUniform1i", "glUniform1iARB", validContext);
    setGLExtensionFuncPtr(glUniform2i, "glUniform2i", "glUniform2iARB", validContext);
    setGLExtensionFuncPtr(glUniform3i, "glUniform3i", "glUniform3iARB", validContext);
    setGLExtensionFuncPtr(glUniform4i, "glUniform4i", "glUniform4iARB", validContext);
    setGLExtensionFuncPtr(glUniform1fv, "glUniform1fv", "glUniform1fvARB", validContext);
    setGLExtensionFuncPtr(glUniform2fv, "glUniform2fv", "glUniform2fvARB", validContext);
    setGLExtensionFuncPtr(glUniform3fv, "glUniform3fv", "glUniform3fvARB", validContext);
    setGLExtensionFuncPtr(glUniform4fv, "glUniform4fv", "glUniform4fvARB", validContext);
    setGLExtensionFuncPtr(glUniform1iv, "glUniform1iv", "glUniform1ivARB", validContext);
    setGLExtensionFuncPtr(glUniform2iv, "glUniform2iv", "glUniform2ivARB", validContext);
    setGLExtensionFuncPtr(glUniform3iv, "glUniform3iv", "glUniform3ivARB", validContext);
    setGLExtensionFuncPtr(glUniform4iv, "glUniform4iv", "glUniform4ivARB", validContext);
    setGLExtensionFuncPtr(glUniformMatrix2fv, "glUniformMatrix2fv", "glUniformMatrix2fvARB", validContext);
    setGLExtensionFuncPtr(glUniformMatrix3fv, "glUniformMatrix3fv", "glUniformMatrix3fvARB", validContext);
    setGLExtensionFuncPtr(glUniformMatrix4fv, "glUniformMatrix4fv", "glUniformMatrix4fvARB", validContext);
    setGLExtensionFuncPtr(glValidateProgram, "glValidateProgram", "glValidateProgramARB", validContext);

    setGLExtensionFuncPtr(glVertexAttrib1d, "glVertexAttrib1d", "glVertexAttrib1dARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib1dv, "glVertexAttrib1dv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib1f, "glVertexAttrib1f", "glVertexAttrib1fARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib1fv, "glVertexAttrib1fv", "glVertexAttrib1fvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib1s, "glVertexAttrib1s", "glVertexAttrib1sARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib1sv, "glVertexAttrib1sv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2d, "glVertexAttrib2d", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2dv, "glVertexAttrib2dv", "glVertexAttrib2dvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2f, "glVertexAttrib2f", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2fv, "glVertexAttrib2fv", "glVertexAttrib2fvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2s, "glVertexAttrib2s", validContext);
    setGLExtensionFuncPtr(glVertexAttrib2sv, "glVertexAttrib2sv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3d, "glVertexAttrib3d", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3dv, "glVertexAttrib3dv", "glVertexAttrib3dvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3f, "glVertexAttrib3f", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3fv, "glVertexAttrib3fv", "glVertexAttrib3fvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3s, "glVertexAttrib3s", validContext);
    setGLExtensionFuncPtr(glVertexAttrib3sv, "glVertexAttrib3sv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nbv, "glVertexAttrib4Nbv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Niv, "glVertexAttrib4Niv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nsv, "glVertexAttrib4Nsv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nub, "glVertexAttrib4Nub", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nubv, "glVertexAttrib4Nubv", "glVertexAttrib4NubvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nuiv, "glVertexAttrib4Nuiv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4Nusv, "glVertexAttrib4Nusv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4bv, "glVertexAttrib4bv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4d, "glVertexAttrib4d", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4dv, "glVertexAttrib4dv", "glVertexAttrib4dvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4f, "glVertexAttrib4f", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4fv, "glVertexAttrib4fv", "glVertexAttrib4fvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4iv, "glVertexAttrib4iv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4s, "glVertexAttrib4s", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4sv, "glVertexAttrib4sv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4ubv, "glVertexAttrib4ubv", "glVertexAttrib4ubvARB", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4uiv, "glVertexAttrib4uiv", validContext);
    setGLExtensionFuncPtr(glVertexAttrib4usv, "glVertexAttrib4usv", validContext);

    setGLExtensionFuncPtr(glVertexAttribPointer, "glVertexAttribPointer","glVertexAttribPointerARB", validContext);
    setGLExtensionFuncPtr(glVertexAttribIPointer, "glVertexAttribIPointer","glVertexAttribIPointerARB", validContext);
    setGLExtensionFuncPtr(glVertexAttribLPointer, "glVertexAttribLPointer","glVertexAttribLPointerARB", validContext);
    setGLExtensionFuncPtr(glVertexAttribDivisor, "glVertexAttribDivisor", validContext);

    // v1.5-only ARB entry points, in case they're needed for fallback
    setGLExtensionFuncPtr(glGetInfoLogARB, "glGetInfoLogARB", validContext);
    setGLExtensionFuncPtr(glGetObjectParameterivARB, "glGetObjectParameterivARB", validContext);
    setGLExtensionFuncPtr(glDeleteObjectARB, "glDeleteObjectARB", validContext);
    setGLExtensionFuncPtr(glGetHandleARB, "glGetHandleARB", validContext);

    // GL 2.1
    setGLExtensionFuncPtr(glUniformMatrix2x3fv, "glUniformMatrix2x3fv", validContext);
    setGLExtensionFuncPtr(glUniformMatrix3x2fv, "glUniformMatrix3x2fv", validContext);
    setGLExtensionFuncPtr(glUniformMatrix2x4fv, "glUniformMatrix2x4fv", validContext);
    setGLExtensionFuncPtr(glUniformMatrix4x2fv, "glUniformMatrix4x2fv", validContext);
    setGLExtensionFuncPtr(glUniformMatrix3x4fv, "glUniformMatrix3x4fv", validContext);
    setGLExtensionFuncPtr(glUniformMatrix4x3fv, "glUniformMatrix4x3fv", validContext);

    // ARB_clip_control
    setGLExtensionFuncPtr(glClipControl, "glClipControl", validContext);

    // EXT_geometry_shader4
    setGLExtensionFuncPtr(glProgramParameteri,  "glProgramParameteri", "glProgramParameteriEXT", validContext);

    // ARB_tesselation_shader
    setGLExtensionFuncPtr(glPatchParameteri, "glPatchParameteri", validContext);
    setGLExtensionFuncPtr(glPatchParameterfv, "glPatchParameterfv", validContext);

    // EXT_gpu_shader4
    setGLExtensionFuncPtr(glGetUniformuiv,  "glGetUniformuiv", "glGetUniformuivEXT", validContext);
    setGLExtensionFuncPtr(glBindFragDataLocation,  "glBindFragDataLocation", "glBindFragDataLocationEXT", validContext);
    setGLExtensionFuncPtr(glBindFragDataLocationIndexed,  "glBindFragDataLocationIndexed", "glBindFragDataLocationIndexedEXT", validContext);
    setGLExtensionFuncPtr(glGetFragDataIndex,  "glGetFragDataIndex", "glGetFragDataIndexEXT", validContext);
    setGLExtensionFuncPtr(glGetFragDataLocation,  "glGetFragDataLocation", "glGetFragDataLocationEXT", validContext);
    setGLExtensionFuncPtr(glUniform1ui,  "glUniform1ui", "glUniform1uiEXT", validContext);
    setGLExtensionFuncPtr(glUniform2ui,  "glUniform2ui", "glUniform2uiEXT", validContext);
    setGLExtensionFuncPtr(glUniform3ui,  "glUniform3ui", "glUniform3uiEXT", validContext);
    setGLExtensionFuncPtr(glUniform4ui,  "glUniform4ui", "glUniform4uiEXT", validContext);
    setGLExtensionFuncPtr(glUniform1uiv,  "glUniform1uiv", "glUniform1uivEXT", validContext);
    setGLExtensionFuncPtr(glUniform2uiv,  "glUniform2uiv", "glUniform2uivEXT", validContext);
    setGLExtensionFuncPtr(glUniform3uiv,  "glUniform3uiv", "glUniform3uivEXT", validContext);
    setGLExtensionFuncPtr(glUniform4uiv,  "glUniform4uiv", "glUniform4uivEXT", validContext);

    // ARB_gpu_shader_int64
    setGLExtensionFuncPtr(glUniform1i64,  "glUniform1i64",  "glUniform1i64ARB",  validContext);
    setGLExtensionFuncPtr(glUniform1ui64, "glUniform1ui64", "glUniform1ui64ARB", validContext);
    setGLExtensionFuncPtr(glUniform2i64,  "glUniform2i64",  "glUniform2i64ARB",  validContext);
    setGLExtensionFuncPtr(glUniform2ui64, "glUniform2ui64", "glUniform2ui64ARB", validContext);
    setGLExtensionFuncPtr(glUniform3i64,  "glUniform3i64",  "glUniform3i64ARB",  validContext);
    setGLExtensionFuncPtr(glUniform3ui64, "glUniform3ui64", "glUniform3ui64ARB", validContext);
    setGLExtensionFuncPtr(glUniform4i64,  "glUniform4i64",  "glUniform4i64ARB",  validContext);
    setGLExtensionFuncPtr(glUniform4ui64, "glUniform4ui64", "glUniform4ui64ARB", validContext);
    setGLExtensionFuncPtr(glUniform1i64v, "glUniform1i64v", "glUniform1i64vARB", validContext);
    setGLExtensionFuncPtr(glUniform1ui64v,"glUniform1ui64v","glUniform1ui64vARB",validContext);
    setGLExtensionFuncPtr(glUniform2i64v, "glUniform2i64v", "glUniform2i64vARB", validContext);
    setGLExtensionFuncPtr(glUniform2ui64v,"glUniform2ui64v","glUniform2ui64vARB",validContext);
    setGLExtensionFuncPtr(glUniform3i64v, "glUniform3i64v", "glUniform3i64vARB", validContext);
    setGLExtensionFuncPtr(glUniform3ui64v,"glUniform3ui64v","glUniform3ui64vARB",validContext);
    setGLExtensionFuncPtr(glUniform4i64v, "glUniform4i64v", "glUniform4i64vARB", validContext);
    setGLExtensionFuncPtr(glUniform4ui64v,"glUniform4ui64v","glUniform4ui64vARB",validContext);

    // ARB_uniform_buffer_object
    setGLExtensionFuncPtr(glGetUniformIndices, "glGetUniformIndices", validContext);
    setGLExtensionFuncPtr(glGetActiveUniformsiv, "glGetActiveUniformsiv", validContext);
    setGLExtensionFuncPtr(glGetActiveUniformName, "glGetActiveUniformName", validContext);
    setGLExtensionFuncPtr(glGetUniformBlockIndex, "glGetUniformBlockIndex", validContext);
    setGLExtensionFuncPtr(glGetActiveUniformBlockiv, "glGetActiveUniformBlockiv", validContext);
    setGLExtensionFuncPtr(glGetActiveUniformBlockName, "glGetActiveUniformBlockName", validContext);
    setGLExtensionFuncPtr(glUniformBlockBinding, "glUniformBlockBinding", validContext);

    // ARB_get_program_binary
    setGLExtensionFuncPtr(glGetProgramBinary, "glGetProgramBinary", validContext);
    setGLExtensionFuncPtr(glProgramBinary, "glProgramBinary", validContext);

    // ARB_gpu_shader_fp64
    setGLExtensionFuncPtr(glUniform1d, "glUniform1d" , validContext);
    setGLExtensionFuncPtr(glUniform2d, "glUniform2d" , validContext);
    setGLExtensionFuncPtr(glUniform3d, "glUniform3d" , validContext);
    setGLExtensionFuncPtr(glUniform4d, "glUniform4d" , validContext);
    setGLExtensionFuncPtr(glUniform1dv, "glUniform1dv" , validContext);
    setGLExtensionFuncPtr(glUniform2dv, "glUniform2dv" , validContext);
    setGLExtensionFuncPtr(glUniform3dv, "glUniform3dv" , validContext);
    setGLExtensionFuncPtr(glUniform4dv, "glUniform4dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix2dv, "glUniformMatrix2dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix3dv, "glUniformMatrix3dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix4dv, "glUniformMatrix4dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix2x3dv,  "glUniformMatrix2x3dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix3x2dv,  "glUniformMatrix3x2dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix2x4dv,  "glUniformMatrix2x4dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix4x2dv,  "glUniformMatrix4x2dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix3x4dv,  "glUniformMatrix3x4dv" , validContext);
    setGLExtensionFuncPtr(glUniformMatrix4x3dv,  "glUniformMatrix4x3dv" , validContext);

    // ARB_shader_atomic_counters
    setGLExtensionFuncPtr(glGetActiveAtomicCounterBufferiv,  "glGetActiveAtomicCounterBufferiv" , validContext);

    // ARB_compute_shader
    setGLExtensionFuncPtr(glDispatchCompute,  "glDispatchCompute" , validContext);


    setGLExtensionFuncPtr(glMemoryBarrier,  "glMemoryBarrier", "glMemoryBarrierEXT" , validContext);

    // BufferObject extensions
    setGLExtensionFuncPtr(glGenBuffers, "glGenBuffers","glGenBuffersARB", validContext);
    setGLExtensionFuncPtr(glBindBuffer, "glBindBuffer","glBindBufferARB", validContext);
    setGLExtensionFuncPtr(glBufferData, "glBufferData","glBufferDataARB", validContext);
    setGLExtensionFuncPtr(glBufferSubData, "glBufferSubData","glBufferSubDataARB", validContext);
    setGLExtensionFuncPtr(glDeleteBuffers, "glDeleteBuffers","glDeleteBuffersARB", validContext);
    setGLExtensionFuncPtr(glIsBuffer, "glIsBuffer","glIsBufferARB", validContext);
    setGLExtensionFuncPtr(glGetBufferSubData, "glGetBufferSubData","glGetBufferSubDataARB", validContext);
    setGLExtensionFuncPtr(glMapBuffer, "glMapBuffer","glMapBufferARB", validContext);
    setGLExtensionFuncPtr(glMapBufferRange,  "glMapBufferRange", "glMapBufferRangeARB" , validContext);
    setGLExtensionFuncPtr(glUnmapBuffer, "glUnmapBuffer","glUnmapBufferARB", validContext);
    setGLExtensionFuncPtr(glGetBufferParameteriv, "glGetBufferParameteriv","glGetBufferParameterivARB", validContext);
    setGLExtensionFuncPtr(glGetBufferPointerv, "glGetBufferPointerv","glGetBufferPointervARB", validContext);
    setGLExtensionFuncPtr(glBindBufferRange, "glBindBufferRange", validContext);
    setGLExtensionFuncPtr(glBindBufferBase,  "glBindBufferBase", "glBindBufferBaseEXT", "glBindBufferBaseNV" , validContext);
    setGLExtensionFuncPtr(glTexBuffer, "glTexBuffer","glTexBufferARB" , validContext);

    isVBOSupported = validContext && (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES || osg::isGLExtensionSupported(contextID,"GL_ARB_vertex_buffer_object"));
    isPBOSupported = validContext && (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES || osg::isGLExtensionSupported(contextID,"GL_ARB_pixel_buffer_object"));
    isTBOSupported = validContext && osg::isGLExtensionSupported(contextID,"GL_ARB_texture_buffer_object");
    isVAOSupported = validContext && (OSG_GLES3_FEATURES || OSG_GL3_FEATURES  || osg::isGLExtensionSupported(contextID, "GL_ARB_vertex_array_object", "GL_OES_vertex_array_object"));
    isTransformFeedbackSupported = validContext && osg::isGLExtensionSupported(contextID, "GL_ARB_transform_feedback2");
    isBufferObjectSupported = isVBOSupported && isPBOSupported;


    // BlendFunc extensions
    isBlendFuncSeparateSupported = validContext &&
                                    (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES ||
                                    osg::isGLExtensionSupported(contextID, "GL_EXT_blend_func_separate") ||
                                    (glVersion >= 1.4f));

    setGLExtensionFuncPtr(glBlendFuncSeparate, "glBlendFuncSeparate", "glBlendFuncSeparateEXT", validContext);

    setGLExtensionFuncPtr(glBlendFunci, "glBlendFunci", "glBlendFunciARB", validContext);
    setGLExtensionFuncPtr(glBlendFuncSeparatei, "glBlendFuncSeparatei", "glBlendFuncSeparateiARB", validContext);


    isSecondaryColorSupported = validContext && isGLExtensionSupported(contextID,"GL_EXT_secondary_color");
    isFogCoordSupported = validContext && isGLExtensionSupported(contextID,"GL_EXT_fog_coord");
    isMultiTexSupported = validContext && isGLExtensionSupported(contextID,"GL_ARB_multitexture");
    isOcclusionQuerySupported = validContext && osg::isGLExtensionSupported(contextID, "GL_NV_occlusion_query");
    isARBOcclusionQuerySupported = validContext && (OSG_GL3_FEATURES || osg::isGLExtensionSupported(contextID, "GL_ARB_occlusion_query"));

    isTimerQuerySupported = validContext && osg::isGLExtensionSupported(contextID, "GL_EXT_timer_query");
    isARBTimerQuerySupported = validContext && osg::isGLExtensionSupported(contextID, "GL_ARB_timer_query");


    setGLExtensionFuncPtr(glDrawArraysInstanced, "glDrawArraysInstanced","glDrawArraysInstancedARB","glDrawArraysInstancedEXT", validContext);
    setGLExtensionFuncPtr(glDrawElementsInstanced, "glDrawElementsInstanced","glDrawElementsInstancedARB","glDrawElementsInstancedEXT", validContext);


    setGLExtensionFuncPtr(glFogCoordfv, "glFogCoordfv","glFogCoordfvEXT", validContext);
    setGLExtensionFuncPtr(glSecondaryColor3ubv, "glSecondaryColor3ubv","glSecondaryColor3ubvEXT", validContext);
    setGLExtensionFuncPtr(glSecondaryColor3fv, "glSecondaryColor3fv","glSecondaryColor3fvEXT", validContext);

    setGLExtensionFuncPtr(glMultiTexCoord1f, "glMultiTexCoord1f","glMultiTexCoord1fARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord4f, "glMultiTexCoord4f","glMultiTexCoord4fARB", validContext);

    setGLExtensionFuncPtr(glMultiTexCoord1fv, "glMultiTexCoord1fv","glMultiTexCoord1fvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord2fv, "glMultiTexCoord2fv","glMultiTexCoord2fvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord3fv, "glMultiTexCoord3fv","glMultiTexCoord3fvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord4fv, "glMultiTexCoord4fv","glMultiTexCoord4fvARB", validContext);


    setGLExtensionFuncPtr(glMultiTexCoord1d, "glMultiTexCoord1d","glMultiTexCoord1dARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord1dv, "glMultiTexCoord1dv","glMultiTexCoord1dvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord2dv, "glMultiTexCoord2dv","glMultiTexCoord2dvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord3dv, "glMultiTexCoord3dv","glMultiTexCoord3dvARB", validContext);
    setGLExtensionFuncPtr(glMultiTexCoord4dv, "glMultiTexCoord4dv","glMultiTexCoord4dvARB", validContext);

    setGLExtensionFuncPtr(glGenOcclusionQueries, "glGenOcclusionQueries","glGenOcclusionQueriesNV", validContext);
    setGLExtensionFuncPtr(glDeleteOcclusionQueries, "glDeleteOcclusionQueries","glDeleteOcclusionQueriesNV", validContext);
    setGLExtensionFuncPtr(glIsOcclusionQuery, "glIsOcclusionQuery","glIsOcclusionQueryNV", validContext);
    setGLExtensionFuncPtr(glBeginOcclusionQuery, "glBeginOcclusionQuery","glBeginOcclusionQueryNV", validContext);
    setGLExtensionFuncPtr(glEndOcclusionQuery, "glEndOcclusionQuery","glEndOcclusionQueryNV", validContext);
    setGLExtensionFuncPtr(glGetOcclusionQueryiv, "glGetOcclusionQueryiv","glGetOcclusionQueryivNV", validContext);
    setGLExtensionFuncPtr(glGetOcclusionQueryuiv, "glGetOcclusionQueryuiv","glGetOcclusionQueryuivNV", validContext);

    setGLExtensionFuncPtr(glGenQueries, "glGenQueries", "glGenQueriesARB", validContext);
    setGLExtensionFuncPtr(glDeleteQueries, "glDeleteQueries", "glDeleteQueriesARB", validContext);
    setGLExtensionFuncPtr(glIsQuery, "glIsQuery", "glIsQueryARB", validContext);
    setGLExtensionFuncPtr(glBeginQuery, "glBeginQuery", "glBeginQueryARB", validContext);
    setGLExtensionFuncPtr(glEndQuery, "glEndQuery", "glEndQueryARB", validContext);
    setGLExtensionFuncPtr(glBeginQueryIndexed, "glBeginQueryIndexed", "glBeginQueryIndexedARB", validContext);
    setGLExtensionFuncPtr(glEndQueryIndexed, "glEndQueryIndexed", "glEndQueryIndexedARB", validContext);
    setGLExtensionFuncPtr(glGetQueryiv, "glGetQueryiv", "glGetQueryivARB", validContext);
    setGLExtensionFuncPtr(glGetQueryObjectiv, "glGetQueryObjectiv","glGetQueryObjectivARB", validContext);
    setGLExtensionFuncPtr(glGetQueryObjectuiv, "glGetQueryObjectuiv","glGetQueryObjectuivARB", validContext);
    setGLExtensionFuncPtr(glGetQueryObjectui64v, "glGetQueryObjectui64v","glGetQueryObjectui64vEXT", validContext);
    setGLExtensionFuncPtr(glQueryCounter, "glQueryCounter", validContext);
    setGLExtensionFuncPtr(glGetInteger64v, "glGetInteger64v", validContext);


    // SampleMaski functionality
    isTextureMultisampleSupported = validContext && isGLExtensionSupported(contextID, "GL_ARB_texture_multisample");
    isOpenGL32upported = (glVersion >= 3.2f);

    // function pointers
    setGLExtensionFuncPtr(glSampleMaski, "glSampleMaski", validContext);
    isSampleMaskiSupported = validContext && (isOpenGL32upported || isGLExtensionSupported(contextID,"ARB_texture_multisample"));


    // old styple Vertex/Fragment Programs
    isVertexProgramSupported = validContext && isGLExtensionSupported(contextID,"GL_ARB_vertex_program");
    isFragmentProgramSupported = validContext && isGLExtensionSupported(contextID,"GL_ARB_fragment_program");

    setGLExtensionFuncPtr(glBindProgram,"glBindProgramARB", validContext);
    setGLExtensionFuncPtr(glGenPrograms, "glGenProgramsARB", validContext);
    setGLExtensionFuncPtr(glDeletePrograms, "glDeleteProgramsARB", validContext);
    setGLExtensionFuncPtr(glProgramString, "glProgramStringARB", validContext);
    setGLExtensionFuncPtr(glProgramLocalParameter4fv, "glProgramLocalParameter4fvARB", validContext);

    // Sample Extensions (OpenGL>=3.3)
    setGLExtensionFuncPtr(glSamplerParameteri, "glSamplerParameteri", "glSamplerParameteriARB", validContext);
    setGLExtensionFuncPtr(glSamplerParameterf, "glSamplerParameterf", "glSamplerParameterfARB", validContext);
    setGLExtensionFuncPtr(glSamplerParameteriv, "glSamplerParameteriv", "glSamplerParameterivARB", validContext);
    setGLExtensionFuncPtr(glSamplerParameterfv, "glSamplerParameterfv", "glSamplerParameterfvARB", validContext);
    setGLExtensionFuncPtr(glSamplerParameterIiv, "glSamplerParameterIiv", "glSamplerParameterIivARB", validContext);
    setGLExtensionFuncPtr(glSamplerParameterIuiv, "glSamplerParameterIuiv", "glSamplerParameterIuivARB", validContext);

    setGLExtensionFuncPtr(glGetSamplerParameteriv, "glGetSamplerParameteriv", "glGetSamplerParameterivARB", validContext);
    setGLExtensionFuncPtr(glGetSamplerParameterfv, "glGetSamplerParameterfv", "glGetSamplerParameterfvARB", validContext);
    setGLExtensionFuncPtr(glGetSamplerParameterIiv, "glGetSamplerParameterIiv", "glGetSamplerParameterIivARB", validContext);
    setGLExtensionFuncPtr(glGetSamplerParameterIuiv, "glGetSamplerParameterIuiv", "glGetSamplerParameterIuivARB", validContext);

    setGLExtensionFuncPtr(glGenSamplers, "glGenSamplers", "glGenSamplersARB", validContext);
    setGLExtensionFuncPtr(glDeleteSamplers, "glDeleteSamplers", "glDeleteSamplersARB", validContext);
    setGLExtensionFuncPtr(glBindSampler, "glBindSampler", "glBindSamplerARB", validContext);
    setGLExtensionFuncPtr(glIsSampler, "glIsSampler", "glIsSamplerARB", validContext);

    // Texture extensions
    const char* renderer = validContext ? (const char*) glGetString(GL_RENDERER) : 0;
    std::string rendererString(renderer ? renderer : "");

    bool radeonHardwareDetected = (rendererString.find("Radeon")!=std::string::npos || rendererString.find("RADEON")!=std::string::npos);
    bool fireGLHardwareDetected = (rendererString.find("FireGL")!=std::string::npos || rendererString.find("FIREGL")!=std::string::npos);

    bool builtInSupport = OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES;

    isMultiTexturingSupported = validContext &&
                                (builtInSupport || OSG_GLES1_FEATURES ||
                                 isGLExtensionOrVersionSupported( contextID,"GL_ARB_multitexture", 1.3f) ||
                                 isGLExtensionOrVersionSupported(contextID,"GL_EXT_multitexture", 1.3f));

    isTextureFilterAnisotropicSupported = validContext && isGLExtensionSupported(contextID,"GL_EXT_texture_filter_anisotropic");
    isTextureSwizzleSupported = validContext && isGLExtensionSupported(contextID,"GL_ARB_texture_swizzle");
    isTextureCompressionARBSupported = validContext && (builtInSupport || isGLExtensionOrVersionSupported(contextID,"GL_ARB_texture_compression", 1.3f));
    isTextureCompressionS3TCSupported = validContext && (isGLExtensionSupported(contextID,"GL_EXT_texture_compression_s3tc") || isGLExtensionSupported(contextID, "GL_S3_s3tc"));
    isTextureCompressionPVRTC2BPPSupported = validContext && isGLExtensionSupported(contextID,"GL_IMG_texture_compression_pvrtc");
    isTextureCompressionPVRTC4BPPSupported = isTextureCompressionPVRTC2BPPSupported;//covered by same extension
    isTextureCompressionETCSupported = validContext && isGLExtensionSupported(contextID,"GL_OES_compressed_ETC1_RGB8_texture");
    isTextureCompressionETC2Supported = validContext && isGLExtensionSupported(contextID,"GL_ARB_ES3_compatibility");
    isTextureCompressionRGTCSupported = validContext && isGLExtensionSupported(contextID,"GL_EXT_texture_compression_rgtc");
    isTextureCompressionPVRTCSupported = validContext && isGLExtensionSupported(contextID,"GL_IMG_texture_compression_pvrtc");

    isTextureMirroredRepeatSupported = validContext && 
                                       (builtInSupport ||
                                        isGLExtensionOrVersionSupported(contextID,"GL_IBM_texture_mirrored_repeat", 1.4f) ||
                                        isGLExtensionOrVersionSupported(contextID,"GL_ARB_texture_mirrored_repeat", 1.4f));

    isTextureEdgeClampSupported = validContext && 
                                  (builtInSupport ||
                                   isGLExtensionOrVersionSupported(contextID,"GL_EXT_texture_edge_clamp", 1.2f) ||
                                   isGLExtensionOrVersionSupported(contextID,"GL_SGIS_texture_edge_clamp", 1.2f));


    isTextureBorderClampSupported = validContext && 
                                    (OSG_GL3_FEATURES ||
                                     ((OSG_GL1_FEATURES || OSG_GL2_FEATURES) && isGLExtensionOrVersionSupported(contextID,"GL_ARB_texture_border_clamp", 1.3f)) ||
                                     ((OSG_GLES2_FEATURES || OSG_GLES3_FEATURES) && isGLExtensionSupported(contextID,"GL_EXT_texture_border_clamp")));

    isGenerateMipMapSupported = validContext && (builtInSupport || isGLExtensionOrVersionSupported(contextID,"GL_SGIS_generate_mipmap", 1.4f));
    preferGenerateMipmapSGISForPowerOfTwo = (radeonHardwareDetected||fireGLHardwareDetected) ? false : true;
    isTextureMultisampledSupported = validContext && (isGLExtensionSupported(contextID,"GL_ARB_texture_multisample"));
    isShadowSupported = validContext && (OSG_GL3_FEATURES || isGLExtensionSupported(contextID,"GL_ARB_shadow"));
    isShadowAmbientSupported = validContext && (isGLExtensionSupported(contextID,"GL_ARB_shadow_ambient"));
    isClientStorageSupported = validContext && (isGLExtensionSupported(contextID,"GL_APPLE_client_storage"));
    isNonPowerOfTwoTextureMipMappedSupported = validContext && (builtInSupport || isGLExtensionSupported(contextID, "GL_OES_texture_npot") || isGLExtensionOrVersionSupported(contextID, "GL_ARB_texture_non_power_of_two", 2.0));
    isNonPowerOfTwoTextureNonMipMappedSupported = validContext && (isNonPowerOfTwoTextureMipMappedSupported || isGLExtensionSupported(contextID, "GL_APPLE_texture_2D_limited_npot"));
    isTextureIntegerEXTSupported = validContext && (OSG_GL3_FEATURES || isGLExtensionSupported(contextID, "GL_EXT_texture_integer"));

    if (rendererString.find("GeForce FX")!=std::string::npos)
    {
        isNonPowerOfTwoTextureMipMappedSupported = false;
        OSG_INFO<<"Disabling _isNonPowerOfTwoTextureMipMappedSupported for GeForce FX hardware."<<std::endl;
    }

    maxTextureSize=0;
    if (validContext) glGetIntegerv(GL_MAX_TEXTURE_SIZE,&maxTextureSize);

    char *ptr;
    if( (ptr = getenv("OSG_MAX_TEXTURE_SIZE")) != 0)
    {
        GLint osg_max_size = atoi(ptr);

        if (osg_max_size<maxTextureSize)
        {

            maxTextureSize = osg_max_size;
        }
    }

    setGLExtensionFuncPtr(glTexStorage2D,"glTexStorage2D","glTexStorage2DARB", validContext);
    setGLExtensionFuncPtr(glCompressedTexImage2D,"glCompressedTexImage2D","glCompressedTexImage2DARB", validContext);
    setGLExtensionFuncPtr(glCompressedTexSubImage2D,"glCompressedTexSubImage2D","glCompressedTexSubImage2DARB", validContext);
    setGLExtensionFuncPtr(glGetCompressedTexImage,"glGetCompressedTexImage","glGetCompressedTexImageARB", validContext);;
    setGLExtensionFuncPtr(glTexImage2DMultisample, "glTexImage2DMultisample", "glTexImage2DMultisampleARB", validContext);

    setGLExtensionFuncPtr(glTexParameterIiv, "glTexParameterIiv", "glTexParameterIivARB", "glTexParameterIivEXT", validContext);
    setGLExtensionFuncPtr(glTexParameterIuiv, "glTexParameterIuiv", "glTexParameterIuivARB", "glTexParameterIuivEXT", validContext);

    setGLExtensionFuncPtr(glBindImageTexture, "glBindImageTexture", "glBindImageTextureARB", validContext);

    isTextureMaxLevelSupported = (glVersion >= 1.2f);

    isTextureStorageEnabled = validContext && ((glVersion >= 4.2f) || isGLExtensionSupported(contextID, "GL_ARB_texture_storage"));
    if ( (ptr = getenv("OSG_GL_TEXTURE_STORAGE"))  != 0 && isTextureStorageEnabled)
    {
        if (strcmp(ptr,"OFF")==0 || strcmp(ptr,"DISABLE")==0 ) isTextureStorageEnabled = false;
        else isTextureStorageEnabled = true;
    }


    // Texture3D extensions
    isTexture3DFast = validContext && (OSG_GL3_FEATURES || isGLExtensionSupported(contextID,"GL_EXT_texture3D"));

    if (isTexture3DFast) isTexture3DSupported = true;
    else isTexture3DSupported = validContext && (glVersion >= 1.2f);

    maxTexture3DSize = 0;
    if (validContext) glGetIntegerv(GL_MAX_3D_TEXTURE_SIZE, &maxTexture3DSize);

    setGLExtensionFuncPtr(glTexImage3D, "glTexImage3D","glTexImage3DEXT", validContext);
    setGLExtensionFuncPtr(glTexSubImage3D, "glTexSubImage3D","glTexSubImage3DEXT", validContext);
    setGLExtensionFuncPtr(glCompressedTexImage3D, "glCompressedTexImage3D","glCompressedTexImage3DARB", validContext);
    setGLExtensionFuncPtr(glCompressedTexSubImage3D, "glCompressedTexSubImage3D","glCompressedTexSubImage3DARB", validContext);
    setGLExtensionFuncPtr(glCopyTexSubImage3D, "glCopyTexSubImage3D","glCopyTexSubImage3DEXT", validContext);
    setGLExtensionFuncPtr(glBeginConditionalRender, "glBeginConditionalRender", "glBeginConditionalRenderARB");
    setGLExtensionFuncPtr(glEndConditionalRender, "glEndConditionalRender", "glEndConditionalRenderARB");

    // Texture2DArray extensions
    isTexture2DArraySupported = validContext && (OSG_GL3_FEATURES || isGLExtensionSupported(contextID,"GL_EXT_texture_array"));

    max2DSize = 0;
    if (validContext) glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max2DSize);
    maxLayerCount = 0;
    if (validContext) glGetIntegerv(GL_MAX_ARRAY_TEXTURE_LAYERS_EXT, &maxLayerCount);

    // Bindless textures
    setGLExtensionFuncPtr(glGetTextureHandle,             "glGetTextureHandle", "glGetTextureHandleARB","glGetTextureHandleNV", validContext);
    setGLExtensionFuncPtr(glMakeTextureHandleResident,    "glMakeTextureHandleResident", "glMakeTextureHandleResidentARB","glMakeTextureHandleResidentNV", validContext);
    setGLExtensionFuncPtr(glMakeTextureHandleNonResident, "glMakeTextureHandleNonResident", "glMakeTextureHandleNonResidentARB", "glMakeTextureHandleNonResidentNV",validContext);
    setGLExtensionFuncPtr(glUniformHandleui64,            "glUniformHandleui64", "glUniformHandleui64ARB","glUniformHandleui64NV", validContext);
    setGLExtensionFuncPtr(glIsTextureHandleResident,      "glIsTextureHandleResident","glIsTextureHandleResidentARB", "glIsTextureHandleResidentNV", validContext);

    // Blending
    isBlendColorSupported = validContext && 
                            (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES ||
                             isGLExtensionSupported(contextID,"GL_EXT_blend_color") ||
                             (glVersion >= 1.2f));

    setGLExtensionFuncPtr(glBlendColor, "glBlendColor", "glBlendColorEXT", validContext);

    bool bultInSupport = OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES;
    isBlendEquationSupported = validContext && 
                               (bultInSupport ||
                                isGLExtensionSupported(contextID, "GL_EXT_blend_equation") ||
                                (glVersion >= 1.2f));


    isBlendEquationSeparateSupported = validContext && 
                                       (bultInSupport ||
                                        isGLExtensionSupported(contextID, "GL_EXT_blend_equation_separate") ||
                                        (glVersion >= 2.0f));


    isSGIXMinMaxSupported = validContext && isGLExtensionSupported(contextID, "GL_SGIX_blend_alpha_minmax");
    isLogicOpSupported = validContext && isGLExtensionSupported(contextID, "GL_EXT_blend_logic_op");

    setGLExtensionFuncPtr(glBlendEquation, "glBlendEquation", "glBlendEquationEXT", validContext);
    setGLExtensionFuncPtr(glBlendEquationSeparate, "glBlendEquationSeparate", "glBlendEquationSeparateEXT", validContext);

    setGLExtensionFuncPtr(glBlendEquationi, "glBlendEquationi", "glBlendEquationiARB", validContext);
    setGLExtensionFuncPtr(glBlendEquationSeparatei, "glBlendEquationSeparatei", "glBlendEquationSeparateiARB", validContext);


    // glEnablei/glDisabli
    setGLExtensionFuncPtr(glEnablei, "glEnablei", validContext);
    setGLExtensionFuncPtr(glDisablei, "glDisablei", validContext);


    // Stencil`
    isStencilWrapSupported = validContext && isGLExtensionOrVersionSupported(contextID, "GL_EXT_stencil_wrap", 1.4f);
    isStencilTwoSidedSupported = validContext && isGLExtensionSupported(contextID, "GL_EXT_stencil_two_side");
    isOpenGL20Supported = validContext && (glVersion >= 2.0f);
    isSeparateStencilSupported = validContext && isGLExtensionSupported(contextID, "GL_ATI_separate_stencil");

    // function pointers
    setGLExtensionFuncPtr(glActiveStencilFace, "glActiveStencilFaceEXT", validContext);
    setGLExtensionFuncPtr(glStencilOpSeparate, "glStencilOpSeparate", "glStencilOpSeparateATI", validContext);
    setGLExtensionFuncPtr(glStencilMaskSeparate, "glStencilMaskSeparate", validContext);
    setGLExtensionFuncPtr(glStencilFuncSeparate, "glStencilFuncSeparate", "glStencilFuncSeparateATI", validContext);
    setGLExtensionFuncPtr(glStencilFuncSeparateATI, "glStencilFuncSeparateATI", validContext);


    // Color Mask
    setGLExtensionFuncPtr(glColorMaski, "glColorMaski", "glColorMaskiARB", validContext);


    // ClampColor
    isClampColorSupported = validContext &&
                            (OSG_GL3_FEATURES ||
                             isGLExtensionSupported(contextID,"GL_ARB_color_buffer_float") ||
                             (glVersion >= 2.0f));

    setGLExtensionFuncPtr(glClampColor, "glClampColor", "glClampColorARB", validContext);


    // PrimitiveRestartIndex
    setGLExtensionFuncPtr(glPrimitiveRestartIndex, "glPrimitiveRestartIndex", "glPrimitiveRestartIndexNV", validContext);


    // Point
    isPointParametersSupported = validContext &&
                                 (OSG_GL3_FEATURES || (glVersion >= 1.4f)  ||
                                  isGLExtensionSupported(contextID,"GL_ARB_point_parameters") ||
                                  isGLExtensionSupported(contextID,"GL_EXT_point_parameters") ||
                                  isGLExtensionSupported(contextID,"GL_SGIS_point_parameters"));


    isPointSpriteSupported = validContext && (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES || isGLExtensionSupported(contextID, "GL_ARB_point_sprite") || isGLExtensionSupported(contextID, "GL_OES_point_sprite") || isGLExtensionSupported(contextID, "GL_NV_point_sprite"));
    isPointSpriteCoordOriginSupported = validContext && (OSG_GL3_FEATURES || (glVersion >= 2.0f));


    setGLExtensionFuncPtr(glPointParameteri, "glPointParameteri", "glPointParameteriARB", validContext);
    if (!glPointParameteri) setGLExtensionFuncPtr(glPointParameteri, "glPointParameteriEXT", "glPointParameteriSGIS", validContext);

    setGLExtensionFuncPtr(glPointParameterf, "glPointParameterf", "glPointParameterfARB", validContext);
    if (!glPointParameterf) setGLExtensionFuncPtr(glPointParameterf, "glPointParameterfEXT", "glPointParameterfSGIS", validContext);

    setGLExtensionFuncPtr(glPointParameterfv, "glPointParameterfv", "glPointParameterfvARB", validContext);
    if (!glPointParameterfv) setGLExtensionFuncPtr(glPointParameterfv, "glPointParameterfvEXT", "glPointParameterfvSGIS", validContext);


    // Multisample
    isMultisampleSupported = validContext && (OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES || isGLExtensionSupported(contextID,"GL_ARB_multisample"));
    isMultisampleFilterHintSupported = validContext && isGLExtensionSupported(contextID, "GL_NV_multisample_filter_hint");

    setGLExtensionFuncPtr(glSampleCoverage, "glSampleCoverage", "glSampleCoverageARB", validContext);


    // FrameBufferObject
    setGLExtensionFuncPtr(glBindRenderbuffer, "glBindRenderbuffer", "glBindRenderbufferEXT", "glBindRenderbufferOES", validContext);
    setGLExtensionFuncPtr(glDeleteRenderbuffers, "glDeleteRenderbuffers", "glDeleteRenderbuffersEXT", "glDeleteRenderbuffersOES", validContext);
    setGLExtensionFuncPtr(glGenRenderbuffers, "glGenRenderbuffers", "glGenRenderbuffersEXT", "glGenRenderbuffersOES", validContext);
    setGLExtensionFuncPtr(glRenderbufferStorage, "glRenderbufferStorage", "glRenderbufferStorageEXT", "glRenderbufferStorageOES", validContext);
    setGLExtensionFuncPtr(glRenderbufferStorageMultisample, "glRenderbufferStorageMultisample", "glRenderbufferStorageMultisampleEXT", "glRenderbufferStorageMultisampleOES", validContext);
    setGLExtensionFuncPtr(glRenderbufferStorageMultisampleCoverageNV, "glRenderbufferStorageMultisampleCoverageNV", validContext);
    setGLExtensionFuncPtr(glBindFramebuffer, "glBindFramebuffer", "glBindFramebufferEXT", "glBindFramebufferOES", validContext);
    setGLExtensionFuncPtr(glDeleteFramebuffers, "glDeleteFramebuffers", "glDeleteFramebuffersEXT", "glDeleteFramebuffersOES", validContext);
    setGLExtensionFuncPtr(glGenFramebuffers, "glGenFramebuffers", "glGenFramebuffersEXT", "glGenFramebuffersOES", validContext);
    setGLExtensionFuncPtr(glCheckFramebufferStatus, "glCheckFramebufferStatus", "glCheckFramebufferStatusEXT", "glCheckFramebufferStatusOES", validContext);

    setGLExtensionFuncPtr(glFramebufferTexture1D, "glFramebufferTexture1D", "glFramebufferTexture1DEXT", "glFramebufferTexture1DOES", validContext);
    setGLExtensionFuncPtr(glFramebufferTexture2D, "glFramebufferTexture2D", "glFramebufferTexture2DEXT", "glFramebufferTexture2DOES", validContext);
    setGLExtensionFuncPtr(glFramebufferTexture3D, "glFramebufferTexture3D", "glFramebufferTexture3DEXT", "glFramebufferTexture3DOES", validContext);
    setGLExtensionFuncPtr(glFramebufferTexture, "glFramebufferTexture", "glFramebufferTextureEXT", "glFramebufferTextureOES", validContext);
    setGLExtensionFuncPtr(glFramebufferTextureLayer, "glFramebufferTextureLayer", "glFramebufferTextureLayerEXT", "glFramebufferTextureLayerOES", validContext);
    setGLExtensionFuncPtr(glFramebufferTextureFace,  "glFramebufferTextureFace", "glFramebufferTextureFaceEXT", "glFramebufferTextureFaceOES" , validContext);
    setGLExtensionFuncPtr(glFramebufferRenderbuffer, "glFramebufferRenderbuffer", "glFramebufferRenderbufferEXT", "glFramebufferRenderbufferOES", validContext);

    setGLExtensionFuncPtr(glGenerateMipmap, "glGenerateMipmap", "glGenerateMipmapEXT", "glGenerateMipmapOES", validContext);
    setGLExtensionFuncPtr(glBlitFramebuffer, "glBlitFramebuffer", "glBlitFramebufferEXT", "glBlitFramebufferOES", validContext);
    setGLExtensionFuncPtr(glGetRenderbufferParameteriv, "glGetRenderbufferParameteriv", "glGetRenderbufferParameterivEXT", "glGetRenderbufferParameterivOES", validContext);

    isFrameBufferObjectSupported =
        glBindRenderbuffer != 0 &&
        glDeleteRenderbuffers != 0 &&
        glGenRenderbuffers != 0 &&
        glRenderbufferStorage != 0 &&
        glBindFramebuffer != 0 &&
        glDeleteFramebuffers != 0 &&
        glGenFramebuffers != 0 &&
        glCheckFramebufferStatus != 0 &&
        glFramebufferTexture2D != 0 &&
        glFramebufferRenderbuffer != 0 &&
        glGenerateMipmap != 0 &&
        glGetRenderbufferParameteriv != 0 &&
    ( OSG_GLES2_FEATURES || OSG_GLES1_FEATURES || isGLExtensionOrVersionSupported(contextID, "GL_EXT_framebuffer_object",3.0f) );


    isPackedDepthStencilSupported = validContext &&
                                    (OSG_GL3_FEATURES ||
                                     (isGLExtensionSupported(contextID, "GL_EXT_packed_depth_stencil")) ||
                                     (isGLExtensionSupported(contextID, "GL_OES_packed_depth_stencil")));

    //subroutine
    osg::setGLExtensionFuncPtr(glGetSubroutineUniformLocation, "glGetSubroutineUniformLocation", validContext);
    osg::setGLExtensionFuncPtr(glGetActiveSubroutineUniformName, "glGetActiveSubroutineUniformName", validContext);
    osg::setGLExtensionFuncPtr(glGetActiveSubroutineUniformiv, "glGetActiveSubroutineUniformiv", validContext);
    osg::setGLExtensionFuncPtr(glGetSubroutineIndex, "glGetSubroutineIndex", validContext);
    osg::setGLExtensionFuncPtr(glGetActiveSubroutineName, "glGetActiveSubroutineName", validContext);
    osg::setGLExtensionFuncPtr(glGetProgramStageiv, "glGetProgramStageiv", validContext);
    osg::setGLExtensionFuncPtr(glUniformSubroutinesuiv, "glUniformSubroutinesuiv", validContext);
    osg::setGLExtensionFuncPtr(glGetUniformSubroutineuiv, "glGetUniformSubroutineuiv", validContext);


    // Sync
    osg::setGLExtensionFuncPtr(glFenceSync, "glFenceSync", validContext);
    osg::setGLExtensionFuncPtr(glIsSync, "glIsSync", validContext);
    osg::setGLExtensionFuncPtr(glDeleteSync, "glDeleteSync", validContext);
    osg::setGLExtensionFuncPtr(glClientWaitSync, "glClientWaitSync", validContext);
    osg::setGLExtensionFuncPtr(glWaitSync, "glWaitSync", validContext);
    osg::setGLExtensionFuncPtr(glGetSynciv, "glGetSynciv", validContext);

    // Indirect Rendering
    osg::setGLExtensionFuncPtr(glDrawArraysIndirect, "glDrawArraysIndirect", "glDrawArraysIndirectEXT", validContext);
    osg::setGLExtensionFuncPtr(glMultiDrawArraysIndirect, "glMultiDrawArraysIndirect", "glMultiDrawArraysIndirectEXT", validContext);
    osg::setGLExtensionFuncPtr(glDrawElementsIndirect, "glDrawElementsIndirect", "glDrawElementsIndirectEXT", validContext);
    osg::setGLExtensionFuncPtr(glMultiDrawElementsIndirect, "glMultiDrawElementsIndirect", "glMultiDrawElementsIndirectEXT", validContext);

    // Transform Feeedback
    osg::setGLExtensionFuncPtr(glBeginTransformFeedback, "glBeginTransformFeedback", "glBeginTransformFeedbackEXT", validContext);
    osg::setGLExtensionFuncPtr(glEndTransformFeedback, "glEndTransformFeedback", "glEndTransformFeedbackEXT", validContext);
    osg::setGLExtensionFuncPtr(glTransformFeedbackVaryings, "glTransformFeedbackVaryings", "glTransformFeedbackVaryingsEXT", validContext);
    osg::setGLExtensionFuncPtr(glGetTransformFeedbackVarying, "glGetTransformFeedbackVarying", "glGetTransformFeedbackVaryingEXT", validContext);
    osg::setGLExtensionFuncPtr(glBindTransformFeedback, "glBindTransformFeedback", validContext);
    osg::setGLExtensionFuncPtr(glDeleteTransformFeedbacks, "glDeleteTransformFeedbacks", validContext);
    osg::setGLExtensionFuncPtr(glGenTransformFeedbacks, "glGenTransformFeedbacks", validContext);
    osg::setGLExtensionFuncPtr(glIsTransformFeedback, "glIsTransformFeedback", validContext);
    osg::setGLExtensionFuncPtr(glPauseTransformFeedback, "glPauseTransformFeedback", validContext);
    osg::setGLExtensionFuncPtr(glResumeTransformFeedback, "glResumeTransformFeedback", validContext);
    osg::setGLExtensionFuncPtr(glDrawTransformFeedback, "glDrawTransformFeedback", validContext);
    osg::setGLExtensionFuncPtr(glDrawTransformFeedbackStream, "glDrawTransformFeedbackStream", validContext);
    osg::setGLExtensionFuncPtr(glDrawTransformFeedbackInstanced, "glDrawTransformFeedbackInstanced", validContext);
    osg::setGLExtensionFuncPtr(glDrawTransformFeedbackStreamInstanced, "glDrawTransformFeedbackStreamInstanced", validContext);
    osg::setGLExtensionFuncPtr(glCreateTransformFeedbacks, "glCreateTransformFeedbacks", validContext);
    osg::setGLExtensionFuncPtr(glTransformFeedbackBufferBase, "glTransformFeedbackBufferBase", validContext);
    osg::setGLExtensionFuncPtr(glTransformFeedbackBufferRange, "glTransformFeedbackBufferRange", validContext);
    osg::setGLExtensionFuncPtr(glGetTransformFeedbackiv, "glGetTransformFeedbackiv", validContext);
    osg::setGLExtensionFuncPtr(glGetTransformFeedbacki_v, "glGetTransformFeedbacki_v", validContext);
    osg::setGLExtensionFuncPtr(glGetTransformFeedbacki64_v, "glGetTransformFeedbacki64_v", validContext);

    //Vertex Array Object
    osg::setGLExtensionFuncPtr(glGenVertexArrays, "glGenVertexArrays", "glGenVertexArraysOES", validContext);
    osg::setGLExtensionFuncPtr(glBindVertexArray, "glBindVertexArray", "glBindVertexArrayOES", validContext);
    osg::setGLExtensionFuncPtr(glDeleteVertexArrays, "glDeleteVertexArrays", "glDeleteVertexArraysOES", validContext);
    osg::setGLExtensionFuncPtr(glIsVertexArray, "glIsVertexArray", "glIsVertexArrayOES", validContext);

    // OpenGL 4.3 / ARB_vertex_attrib_binding
    isVertexAttribBindingSupported = validContext && (isGLExtensionOrVersionSupported(contextID, "GL_ARB_vertex_attrib_binding", 4.3f));

    osg::setGLExtensionFuncPtr(glBindVertexBuffer, "glBindVertexBuffer", "glBindVertexBufferOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexArrayVertexBuffer, "glVertexArrayVertexBuffer", "glVertexArrayVertexBufferOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexAttribBinding, "glVertexAttribBinding", "glVertexAttribBindingOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexArrayAttribBinding, "glVertexArrayAttribBinding", "glVertexArrayAttribBindingOES", validContext);

    osg::setGLExtensionFuncPtr(glVertexAttribFormat, "glVertexAttribBinding", "glVertexAttribBindingOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexAttribIFormat, "glVertexAttribBinding", "glVertexAttribBindingOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexAttribLFormat, "glVertexAttribLFormat", "glVertexAttribLFormatOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexArrayAttribFormat, "glVertexArrayAttribFormat", "glVertexArrayAttribFormatOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexArrayAttribIFormat, "glVertexArrayAttribIFormat", "glVertexArrayAttribIFormatOES", validContext);
    osg::setGLExtensionFuncPtr(glVertexArrayAttribLFormat, "glVertexArrayAttribLFormat", "glVertexArrayAttribLFormatOES", validContext);

    // MultiDrawArrays
    setGLExtensionFuncPtr(glMultiDrawArrays, "glMultiDrawArrays", "glMultiDrawArraysEXT", validContext);
    setGLExtensionFuncPtr(glMultiDrawElements, "glMultiDrawElements", "glMultiDrawElementsEXT");
    setGLExtensionFuncPtr(glDrawArraysInstancedBaseInstance, "glDrawArraysInstancedBaseInstance", "glDrawArraysInstancedBaseInstanceEXT");
    setGLExtensionFuncPtr(glDrawElementsInstancedBaseInstance, "glDrawElementsInstancedBaseInstance", "glDrawElementsInstancedBaseInstanceEXT");
    setGLExtensionFuncPtr(glDrawElementsInstancedBaseVertexBaseInstance, "glDrawElementsInstancedBaseVertexBaseInstance", "glDrawElementsInstancedBaseVertexBaseInstanceEXT");

    setGLExtensionFuncPtr(glDrawRangeElements, "glDrawRangeElements");
    setGLExtensionFuncPtr(glDrawElementsBaseVertex, "glDrawElementsBaseVertex", "glDrawElementsBaseVertexEXT");
    setGLExtensionFuncPtr(glDrawRangeElementsBaseVertex, "glDrawRangeElementsBaseVertex", "glDrawRangeElementsBaseVertexEXT");
    setGLExtensionFuncPtr(glDrawElementsInstancedBaseVertex, "glDrawElementsInstancedBaseVertex", "glDrawElementsInstancedBaseVertexEXT");
    setGLExtensionFuncPtr(glMultiDrawElementsBaseVertex, "glMultiDrawElementsBaseVertex", "glMultiDrawElementsBaseVertexEXT");
    setGLExtensionFuncPtr(glProvokingVertex, "glProvokingVertex", "glProvokingVertexEXT");

    setGLExtensionFuncPtr(glBeginConditionalRender, "glBeginConditionalRender", "glBeginConditionalRenderEXT");
    setGLExtensionFuncPtr(glEndConditionalRender, "glEndConditionalRender", "glEndConditionalRenderEXT");

    // ViewportArray
    isViewportArraySupported = validContext && (isGLExtensionOrVersionSupported(contextID, "GL_ARB_viewport_array", 4.1f));

    osg::setGLExtensionFuncPtr(glViewportArrayv, "glViewportArrayv", validContext);
    osg::setGLExtensionFuncPtr(glViewportIndexedf, "glViewportIndexedf", validContext);
    osg::setGLExtensionFuncPtr(glViewportIndexedfv, "glViewportIndexedfv", validContext);
    osg::setGLExtensionFuncPtr(glScissorArrayv, "glScissorArrayv", validContext);
    osg::setGLExtensionFuncPtr(glScissorIndexed, "glScissorIndexed", validContext);
    osg::setGLExtensionFuncPtr(glScissorIndexedv, "glScissorIndexedv", validContext);
    osg::setGLExtensionFuncPtr(glDepthRangeArrayv, "glDepthRangeArrayv", validContext);
    osg::setGLExtensionFuncPtr(glDepthRangeIndexed, "glDepthRangeIndexed", validContext);
    osg::setGLExtensionFuncPtr(glDepthRangeIndexedf, "glDepthRangeIndexedfOES", "glDepthRangeIndexedfNV", validContext);
    osg::setGLExtensionFuncPtr(glGetFloati_v, "glGetFloati_v", validContext);
    osg::setGLExtensionFuncPtr(glGetDoublei_v, "glGetDoublei_v", validContext);
    osg::setGLExtensionFuncPtr(glGetIntegerIndexedvEXT, "glGetIntegerIndexedvEXT", validContext);
    osg::setGLExtensionFuncPtr(glEnableIndexedEXT, "glEnableIndexedEXT", validContext);
    osg::setGLExtensionFuncPtr(glDisableIndexedEXT, "glDisableIndexedEXT", validContext);
    osg::setGLExtensionFuncPtr(glIsEnabledIndexedEXT, "glIsEnabledIndexedEXT", validContext);

    setGLExtensionFuncPtr(glClientActiveTexture,"glClientActiveTexture","glClientActiveTextureARB", validContext);
    setGLExtensionFuncPtr(glActiveTexture, "glActiveTexture","glActiveTextureARB", validContext);
    setGLExtensionFuncPtr(glFogCoordPointer, "glFogCoordPointer","glFogCoordPointerEXT", validContext);
    setGLExtensionFuncPtr(glSecondaryColorPointer, "glSecondaryColorPointer","glSecondaryColorPointerEXT", validContext);

    if (validContext)
    {
        if (osg::getGLVersionNumber() >= 2.0 || osg::isGLExtensionSupported(contextID, "GL_ARB_vertex_shader") || OSG_GLES2_FEATURES || OSG_GLES3_FEATURES || OSG_GL3_FEATURES)
        {
            glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,&glMaxTextureUnits);
            #ifdef OSG_GL_FIXED_FUNCTION_AVAILABLE
                glGetIntegerv(GL_MAX_TEXTURE_COORDS, &glMaxTextureCoords);
            #else
                glMaxTextureCoords = glMaxTextureUnits;
            #endif
        }
        #ifdef GL_MAX_TEXTURE_UNITS
        else if ( osg::getGLVersionNumber() >= 1.3 ||
                                    osg::isGLExtensionSupported(contextID,"GL_ARB_multitexture") ||
                                    osg::isGLExtensionSupported(contextID,"GL_EXT_multitexture") ||
                                    OSG_GLES1_FEATURES)
        {
            GLint maxTextureUnits = 0;
            glGetIntegerv(GL_MAX_TEXTURE_UNITS,&maxTextureUnits);
            glMaxTextureUnits = maxTextureUnits;
            glMaxTextureCoords = maxTextureUnits;
        }
        #endif
        else
        {
            glMaxTextureUnits = 1;
            glMaxTextureCoords = 1;
        }
    }
    else
    {
        glMaxTextureUnits = 0;
        glMaxTextureCoords = 0;
    }

    osg::setGLExtensionFuncPtr(glObjectLabel, "glObjectLabel", validContext);

}


///////////////////////////////////////////////////////////////////////////
// C++-friendly convenience methods

GLuint GLExtensions::getCurrentProgram() const
{
    if( glVersion >= 2.0f )
    {
        // GLSL as GL v2.0 core functionality
        GLint result = 0;
        glGetIntegerv( GL_CURRENT_PROGRAM, &result );
        return static_cast<GLuint>(result);
    }
    else if (glGetHandleARB)
    {
        // fallback for GLSL as GL v1.5 ARB extension
#ifndef GL_PROGRAM_OBJECT_ARB
#define GL_PROGRAM_OBJECT_ARB 0x8B40
#endif
        return glGetHandleARB( GL_PROGRAM_OBJECT_ARB );
    }
    else
    {
        OSG_WARN<<"Warning GLExtensions::getCurrentProgram not supported"<<std::endl;;
        return 0;
    }
}


bool GLExtensions::getProgramInfoLog( GLuint program, std::string& result ) const
{
    GLsizei bufLen = 0;        // length of buffer to allocate
    GLsizei strLen = 0;        // strlen GL actually wrote to buffer

    glGetProgramiv( program, GL_INFO_LOG_LENGTH, &bufLen );
    if( bufLen > 1 )
    {
        GLchar* infoLog = new GLchar[bufLen];
        glGetProgramInfoLog( program, bufLen, &strLen, infoLog );
        if( strLen > 0 ) result = reinterpret_cast<char*>(infoLog);
        delete [] infoLog;
    }
    return (strLen > 0);
}


bool GLExtensions::getShaderInfoLog( GLuint shader, std::string& result ) const
{
    GLsizei bufLen = 0;        // length of buffer to allocate
    GLsizei strLen = 0;        // strlen GL actually wrote to buffer

    glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &bufLen );
    if( bufLen > 1 )
    {
        GLchar* infoLog = new GLchar[bufLen];
        glGetShaderInfoLog( shader, bufLen, &strLen, infoLog );
        if( strLen > 0 ) result = reinterpret_cast<char*>(infoLog);
        delete [] infoLog;
    }
    return (strLen > 0);
}


bool GLExtensions::getAttribLocation( const char* attribName, GLuint& location ) const
{
    // is there an active GLSL program?
    GLuint program = getCurrentProgram();
    if( glIsProgram(program) == GL_FALSE ) return false;

    // has that program been successfully linked?
    GLint linked = GL_FALSE;
    glGetProgramiv( program, GL_LINK_STATUS, &linked );
    if( linked == GL_FALSE ) return false;

    // is there such a named attribute?
    GLint loc = glGetAttribLocation( program, reinterpret_cast<const GLchar*>(attribName) );
    if( loc < 0 ) return false;

    location = loc;
    return true;
}


bool GLExtensions::getFragDataLocation( const char* fragDataName, GLuint& location ) const
{
    // is there an active GLSL program?
    GLuint program = getCurrentProgram();
    if( glIsProgram(program) == GL_FALSE ) return false;

    // has that program been successfully linked?
    GLint linked = GL_FALSE;
    glGetProgramiv( program, GL_LINK_STATUS, &linked );
    if( linked == GL_FALSE ) return false;

    // check if supported
    if (glGetFragDataLocation == NULL) return false;

    // is there such a named attribute?
    GLint loc = glGetFragDataLocation( program, reinterpret_cast<const GLchar*>(fragDataName) );
    if( loc < 0 ) return false;

    location = loc;
    return true;
}