OpenGL Loader Generator

OpenGL Loader Generator is a generator of OpenGL loading library targetting C++ that supports different OpenGL versions, profiles, extensions, and even has adjustable code formatting. The generated library loads OpenGL function pointers & can be used in place of system-provided OpenGL header files (which are known to contain definitions for only a few extremely old OpenGL verions). The library has no dependencies other than an OpenGL implementation and a C++11 compiler.

The project has been tested under Linux with GCC 9.2 & under Windows with MinGW 9.3. If for some reason it doesn't work for your platform, be welcome to post an issue or (better) make a PR.

The project is heavily influenced by glLoadGen (no longer supported).

Generation

The generator itself is a single python script generator.py. It needs a configuration file to work, though.

To generate the loading library (header & source files), run ./generator.py config.json

The config file is a single JSON object containing the generator configuration (see the example file). A config file was chosen instead of e.g. command-line arguments to make updating the config & loader easier.

The following generator options are supported:

Option	Type	Default value	Description
spec_file	string	"gl.xml"	Path to OpenGL specification XML file (a version of this file is included in this repository)
api	string	"gl"	The API to load: gl, gles1, gles2 or glsc
version	string	"4.6"	The API version to load
profile	string	"core"	The API profile to load (may be empty)
extensions	[string]	[]	The list of extensions to load
indent	string	"\t"	The string to use as indentation in the generated code
namespace	string	"gl"	The namespace that will be used for generated API functions and constants (empty namespace means using global namespace)
loader_namespace	string	"sys"	The namespace that will be used for the loader library public interface, relative to the gl namespace (empty namespace means using parent namespace)
internal_namespace	string	"internal"	The namespace that will be used for the loader library internals, relative to the gl namespace (empty namespace means using parent namespace)
internal_prefix	string	""	The prefix that will be appended to all OpenGL function names in the loader library internals (not the loaded OpenGL functions)
undef	int	4	All OpenGL constants of this length or shorter will be #undefined in the beginning of the library header (some systems may define TRUE, ZERO, etc)
strip	bool	true	Whether to strip the gl and GL_ prefixes from OpenGL functions and constants (makes sense when using a namespace)
out_header	string	"gl.hpp"	The path to the generated loader library header
out_source	string	"gl.cpp"	The path to the generated loader library source
include	string	"\"${config.out_header}\""	The string to be used by the library source to include the library header (including the "" or <>); that is, the library source will contain a line #include ${config.include}

All non-absolute paths are resolved relative to current working directory.

The generated functions are in C++, thus adhere to C++ linkage & name mangling rules.

Note that options config.namespace = "" and config.strip = false make the generated functions appear in the global namespace with names identical to how they are defined in OpenGL (e.g. glClear in the global namespace, etc). This may interfere with already existing OpenGL functions, use at your own risk (however the library prevents including OpenGL headers alongside itself, and OpenGL functions have C linkage, so it should be hard to actually face any problems).

See the examples of generated header and source for further details on the structure of the generated files.

Usage

With the default settings, the gl namespace contains all OpenGL functions and constants for a particular version & profile, while the loader library API is in the gl::sys namespace. The gl::internal namespace will contain the actual OpenGL functions' pointers that will be loaded at runtime. All of these namespaces can be changed through the configuration file.

To initialize the library, call gl::sys::initialize(). This function returns true if all the required OpenGL functions were successfully loaded (excluding extensions), and false otherwise. To check if a particular requested extension is supported, call gl::sys::ext_EXTENSION_NAME(), e.g. gl::sys::ext_ARB_texture_filter_anisotropic() for the GL_ARB_texture_filter_anisotropic extension (note that the GL_ part is stripped).

The loaded functions and constants can be used like gl::DrawArrays(gl::TRIANGLES, 0, 6) (again, assuming default settings). See the test application for a working example of library usage.

License

The OpenGL Loader Generator is distributed under the MIT license.

Contributing

Any fixes and/or enhancements are warmly welcome. Before creating a pull request, make sure that the test application compiles and runs successfully (you'll need the SDL2 library for that).