xref: /third_party/openGLES/README.adoc

// Copyright 2017-2021 The Khronos Group Inc.
// SPDX-License-Identifier: CC-BY-4.0

= OpenGL-Registry


== OpenGL, OpenGL ES, and OpenGL ES-SC API and Extension Registry

This site contains the API and Extension registries for the OpenGL family
APIs - OpenGL, OpenGL ES, and OpenGL SC. It includes API specifications;
specifications of Khronos- and vendor-approved extensions; header files
corresponding to the specifications; the XML API Registry defining each
API; and related tools and scripts.

It does not contain the OpenGL and OpenGL ES Reference Pages, which are in
the KhronosGroup/OpenGL-Refpages repository.

If you want to add an extension specification to the Registry, correct an
existing specification, request allocation of enumerants and other
controlled resources in the OpenGL / GLX / WGL namespaces, or otherwise
change the Registry, propose a pull request against the OpenGL-Registry
repository and adding the appropriate extension specifications, making changes
to the appropriate XML file, etc. Note that any changes you propose to
reserved values in the registry are not official until your pull request is
*accepted* into the main branch.

Feel free to post issues on the repository if it's unclear how to do
something you need to with extensions, or if you find any problems.


== Please Don't File API And GLSL Bugs Here!

The OpenGL-Registry repository isn't the right place to report problems with
the OpenGL and OpenGL ES API and Shading Language Specifications.

For API (both core and extension) issues, please use the issue tracker in
the https://github.com/KhronosGroup/OpenGL-API repository.

For Shading Language (both core and extension) issues, please use the issue
tracker in the https://github.com/KhronosGroup/OpenGL-GLSL repository.

Please tag your issues with +[OpenGL]+ or +[OpenGL ES]+ in the title, if
they are specific to that API and/or Shading Language.

Reporting problems with the registry *itself*, including missing or badly
formed extension documents, headers, or XML files, should be done using the
OpenGL-Registry issue tracker.


=== Defining New Extensions

To create a new extension specification, take these steps:

* Request one or more blocks of unused enumerants for GL, GLX, or WGL
  depending on the needs of your extension, by adding the reservation(s) to
  the end of gl.xml, glx.xml, and/or wgl.xml.
* Once the pull request modifying the XML files is accepted into main, you
  have control of those enumerant blocks.
* Create an extension specification, following the model of existing vendor
  specifications under extensions/*vendor*/ .
* Obtain whatever degree of review, implementation, and signoff you need
  from affected parties before declaring the extension complete.
* Add the extension specification under extensions/*vendor*/*extension* .
* Modify extensions/registry.py to include the extension, using the next
  free ARB, GL, and/or ES extension numbers (depending on which API the
  extension is defined for). Execute the python script nextfree.py in the
  extensions/ directory to find the next free numbers.
* Once registry.py is updated, 'make' in extensions/ to update the PHP
  include files which are used to show an index of extensions on the
  registry website. This requires GNU make and Python 3.
* Add the extension number(s) to the extension specification in the 'Number'
  block.
* Add the extension interfaces and enumerant assignments to xml/gl.xml,
  glx.xml, and/or wgl.xml following existing examples. Verify that the
  relevant extension headers are generated with the correct interfaces by
  running 'make' in xml/. This requires the lxml Python module.
* Once the pull request adding the extension specification and modifying
  registry.py is accepted, your extension is registered.

There are some documents under the docs/ directory describing some of the
processes for making extensions, but they are largely out of date. They may
be updated or removed over time:

* link:docs/rules.html[How to create extensions]
* link:docs/enums.html[Enumerant allocation policies]
* link:docs/template.txt[Extension specification template]
* link:docs/promoting.html[Extension promotion guidelines]
* link:docs/reserved.txt[GLX opcode registry (rarely updated)]
* link:docs/syntaxrules.txt[OpenGL Syntax Rules (updated 2006/12/13)]
* link:docs/GLSLExtensionRules.txt[OpenGL Shading Language Extension Conventions (updated 2006/12/18)]
* link:docs/fog_coord.txt[Extension Specification Example]


=== Repository Contents

* ABI - OpenGL ABI for Linux
* api - Header files for all APIs
** api/ES - Headers for OpenGL ES
** api/GL - Headers for OpenGL
** api/SC - Headers for OpenGL SC
** Note that the OpenGL ES and OpenGL SC headers all depend on the shared
   https://www.khronos.org/registry/EGL/api/KHR/khrplatform.h[khrplatform.h]
   This file is maintained in the http://www.khronos.org/registry/EGL/[EGL
   Registry].
* docs - Miscellaneous documentation on creating extensions, mostly out of date.
* extensions - Extension specifications for all APIs
** extensions/registry.py - combined extension registry for all APIs
** extensions/makeindex.py - create HTML extension indices from registry.py
* index_{es,gl,sc}.php - Index files for the website, linking to specifications, headers, and extensions relevant to each API
* specs - API and Shading Language Specifications for all APIs
** specs/es - OpenGL ES Specifications
** specs/gl - OpenGL Specifications
** specs/sc - OpenGL SC Specifications
* xml - XML API Registry and related tools


=== There Sure Is A Lot Of Stuff In Here!

Yes, there sure is. The specs/ directory contains over 125 MB of PDFs,
including the latest specs for each version of OpenGL and OpenGL ES. While
this may be somewhat distressing to people who just want to add a single
extension, due to the repository download time, the *primary* purpose of
this repository is to be the backing store for the web registry on
khronos.org. Fortunately git is very efficient, so once you've done the
initial repository clone, updates will be small and quick.