text: # ----------------------------------------------------------------------------
  # pyglet
  # Copyright (c) 2006-2008 Alex Holkner
  # Copyright (c) 2008-2020 pyglet contributors
  # All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions
  # are met:
  #
  #  * Redistributions of source code must retain the above copyright
  #    notice, this list of conditions and the following disclaimer.
  #  * Redistributions in binary form must reproduce the above copyright
  #    notice, this list of conditions and the following disclaimer in
  #    the documentation and/or other materials provided with the
  #    distribution.
  #  * Neither the name of pyglet nor the names of its
  #    contributors may be used to endorse or promote products
  #    derived from this software without specific prior written
  #    permission.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  # COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  # POSSIBILITY OF SUCH DAMAGE.
  # ----------------------------------------------------------------------------
  
  from ctypes import *
  
  import pyglet.lib
  from pyglet.gl.lib import missing_function, decorate_function
  
  from pyglet.compat import asbytes
  
  __all__ = ['link_GL', 'link_GLU', 'link_GLX']
  
  gl_lib = pyglet.lib.load_library('GL')
  glu_lib = pyglet.lib.load_library('GLU')
  
  # Look for glXGetProcAddressARB extension, use it as fallback (for ATI fglrx and DRI drivers).
  try:
      glXGetProcAddressARB = getattr(gl_lib, 'glXGetProcAddressARB')
      glXGetProcAddressARB.restype = POINTER(CFUNCTYPE(None))
      glXGetProcAddressARB.argtypes = [POINTER(c_ubyte)]
      _have_getprocaddress = True
  except AttributeError:
      _have_getprocaddress = False
  
  
  def link_GL(name, restype, argtypes, requires=None, suggestions=None):
      try:
          func = getattr(gl_lib, name)
          func.restype = restype
          func.argtypes = argtypes
          decorate_function(func, name)
          return func
      except AttributeError:
          if _have_getprocaddress:
              # Fallback if implemented but not in ABI
              bname = cast(pointer(create_string_buffer(asbytes(name))), POINTER(c_ubyte))
              addr = glXGetProcAddressARB(bname)
              if addr:
                  ftype = CFUNCTYPE(*((restype,) + tuple(argtypes)))
                  func = cast(addr, ftype)
                  decorate_function(func, name)
                  return func
  
      return missing_function(name, requires, suggestions)
  
  
  link_GLX = link_GL
  
  
  def link_GLU(name, restype, argtypes, requires=None, suggestions=None):
      try:
          func = getattr(glu_lib, name)
          func.restype = restype
          func.argtypes = argtypes
          decorate_function(func, name)
          return func
      except AttributeError:
          return missing_function(name, requires, suggestions)
  