ポイントはrescue節でのwglGetProcAddress

opengl_common.rb

module OpenGL
  def self.bind_command( sym )
    begin
      GL_FUNCTIONS_MAP[sym] = Fiddle::Function.new( @@gl_dll[sym.to_s], 
                                                    GL_FUNCTIONS_ARGS_MAP[sym],
                                                    GL_FUNCTIONS_RETVAL_MAP[sym] )
    rescue Exception => e
      func_ptr = wglGetProcAddress(sym.to_s)
      # p sym.to_s
      GL_FUNCTIONS_MAP[sym] = Fiddle::Function.new( func_ptr,
                                                    GL_FUNCTIONS_ARGS_MAP[sym],
                                                    GL_FUNCTIONS_RETVAL_MAP[sym] )
      raise RuntimeError if GL_FUNCTIONS_RETVAL_MAP[sym] == nil
    end
  end
end

opengl_windows.rb

require 'fiddle'

module OpenGL

  WGL_FUNCTIONS_MAP = {}
  WGL_FUNCTIONS_ARGS_MAP = {}
  WGL_FUNCTIONS_RETVAL_MAP = {}

  def self.get_wgl_command( sym )
    if WGL_FUNCTIONS_MAP[sym] == nil
      bind_wgl_command( sym )
    end
    return WGL_FUNCTIONS_MAP[sym]
  end

  def self.bind_wgl_command( sym )
    WGL_FUNCTIONS_MAP[sym] = Fiddle::Function.new( @@gl_dll[sym.to_s], 
                                                   WGL_FUNCTIONS_ARGS_MAP[sym],
                                                   WGL_FUNCTIONS_RETVAL_MAP[sym] )
    raise RuntimeError if WGL_FUNCTIONS_RETVAL_MAP[sym] == nil
  end

  WGL_FUNCTIONS_ARGS_MAP[:wglGetProcAddress] = [Fiddle::TYPE_VOIDP]
  WGL_FUNCTIONS_RETVAL_MAP[:wglGetProcAddress] = Fiddle::TYPE_VOIDP

  def wglGetProcAddress(_lpszProc_)
    f = OpenGL::get_wgl_command(:wglGetProcAddress)
    f.call(_lpszProc_)
  end

end