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flextGL is an OpenGL extension loader generator.

It is a bit different than other comparable systems:

  • Gives complete control over exposed version and extensions
  • (Optionally) exports only core-profile functions
  • Only requested extensions are loaded
  • Bindings directly generated from the OpenGL registry's gl.xml file
  • Flexible python template system for source-generation
  • Source templates easy to adapt to project requirements
  • Explicitly define the functions that need to be loaded(optional)

You will need the following dependencies:

What's new?

  • January 30 2015: Adding function whitelist and lite template

  • August 7 2014: Adding support for generating OpenGL ES loading code

  • July 10 2014: flextGL now parses gl.xml instead of the deprecated .spec files.

Source tree


    The generator script.


    The parsing code

  • templates/

    The sub-directories in here contain the different template sets. You can add your own template by simply creating a new folder in there.

  • profiles/

    Some example profile files to give you an idea on how to write your own. 'profiles/exampleProfile.txt' contains a lot of comments to get you up to speed.

  • spec/ (generated)

    This directory is automatically created by the script to store the downloaded OpenGL .spec files.


You create your loader code by writing a profile file and passing it to the script.

Here is what a typical profile might look like:

version 3.3 core
extension EXT_texture_filter_anisotropic optional
extension ARB_tesselation_shader optional

This requests an OpenGL core profile and the extensions for anisotropic filtering and tesselation shaders. Those extensions were requested as 'optional'. This means that a missing extension won't cause an error. Instead, the programmer will have to check before using it. This can be easily done by testing a generated global variable. For OpenGL ES a typical profile might look like:

version 3.0 es
extension OES_standard_derivatives optional
extension OES_vertex_array_object optional

The profile file is then passed to the script like this:

$ python -D generated profile.txt

This will create the requested source code and put it in the 'generated' directory.

The best way to work with flextGL is to integrate it in your build-system. The example project demonstrates this for Make and CMake here.

Generated API

The generated API boils down to a few things:

  • int flextInit()

    Initializes the OpenGL functions after context creation.


    The OpenGL major version defined in the profile file.


    The OpenGL minor version defined in the profile file.


    Boolean variable. Is GL_TRUE, if the profile file defined a core profile.

  • FLEXT_<extension-name>

    Generated global variables for checking if a specific extension is supported.

Take a look at the example program to get an idea on how it's used.


At the moment, there are three template sets available:

  • 'compatible'

    This loads the extensions using a framework-agnostic method with WGL AGL or GLX. This is probably a sensible default for most people.

  • 'glfw'

    This uses GLFW 2's functions for loading and testing for OpenGL extensions. It will obviously only work with GLFW, but is well tested and the generated source code is very easy to understand.

  • 'glfw3'

    This works like the glfw template, but uses GLFW 3 instead. In this template, a pointer to the GLFWwindow has to be passed as a parameter of flextInit().

  • 'glfw3-es'

    Used for generating OpenGL ES loading code.

  • 'lite'

    A variant of the compatible template that generates more compact code It has not been thoroughly tested yet, though.

Installing Wheezy Template on Windows

If you have Python 3.4+ installed you should be able to install Wheezy using pip.

$ pip install --user wheezy.template

The --user does a local install in your home-folder. You can omit it if you want to do a system-wide installation.

If you have an older version of Python or don't have pip for some reason, then you need to install it first.


The "compatible" template uses a few code snippets from Slavomir Kaslev's gl3w OpenGL core profile loader for portable loading of procedures and checking minor/major version in OpenGL < 3.0.

Mykhailo Parfeniuk(sopyer) provided most of the gl.xml parsing code.

Vladimír Vondruš(mosra) added support for OpenGL ES loader generation.

Leander Beernaert(LeanderBB) did various fixes on the compatible template.

eternalrain added support for function white-lists and created the lite template.

(C) Thomas Weber, 2011-2015
    ginko (at) cg (dot) tuwien (dot) ac (dot) at