OpenGL超级宝典第5版&&基础渲染

gltools函数库：
int gltIsExtSupported(const char *extension)
     {
    #ifndef OPENGL_ES      
    GLint nNumExtensions;
    glGetIntegerv(GL_NUM_EXTENSIONS, &nNumExtensions);
   
    for(GLint i = 0; i < nNumExtensions; i++)
        if(strcmp(extension, (const char *)glGetStringi(GL_EXTENSIONS, i)) == 0)
           return 1;
    #else
        GLubyte *extensions = NULL;
        const GLubyte *start;
        GLubyte *where, *terminator;
       
        where = (GLubyte *) strchr(extension, ‘ ‘);
        if (where || *extension == ‘\0‘)
            return 0;
       
        extensions = (GLubyte *)glGetString(GL_EXTENSIONS);
       
        start = extensions;
        for (;;)
          {
            where = (GLubyte *) strstr((const char *) start, extension);
           
            if (!where)
                break;
           
            terminator = where + strlen(extension);
           
            if (where == start || *(where - 1) == ‘ ‘)
               {
                if (*terminator == ‘ ‘ || *terminator == ‘\0‘)
                    return 1;
               }
            start = terminator;
          }
    #endif
     return 0;
     }