// Copyright 2015-2021 The Khronos Group, Inc.
//
// SPDX-License-Identifier: CC-BY-4.0


[[introduction]]
= Introduction

This document, referred to as the "`Vulkan Specification`" or just the
"`Specification`" hereafter, describes the Vulkan Application Programming
Interface (API).
Vulkan is a http://www.open-std.org/jtc1/sc22/wg14/www/standards[C99] API
designed for explicit control of low-level graphics and compute
functionality.

The canonical version of the Specification is available in the official
https://www.khronos.org/registry/vulkan/[Vulkan Registry]
(https://www.khronos.org/registry/vulkan/).
The source files used to generate the Vulkan specification are stored in the
https://github.com/KhronosGroup/Vulkan-Docs[Vulkan Documentation Repository]
(https://github.com/KhronosGroup/Vulkan-Docs).
The source repository additionally has a public issue tracker and allows the
submission of pull requests that improve the specification.


[[introduction-conventions]]
== Document Conventions

The Vulkan specification is intended for use by both implementors of the API
and application developers seeking to make use of the API, forming a
contract between these parties.
Specification text may address either party; typically the intended audience
can be inferred from context, though some sections are defined to address
only one of these parties.
(For example, <<fundamentals-validusage>> sections only address application
developers).
Any requirements, prohibitions, recommendations or options defined by
<<introduction-normative-terminology, normative terminology>> are imposed
only on the audience of that text.

[NOTE]
.Note
====
Structure and enumerated types defined in extensions that were promoted to
core in a later version of Vulkan are now defined in terms of the equivalent
Vulkan core interfaces.
This affects the Vulkan Specification, the Vulkan header files, and the
corresponding XML Registry.
====


[[introduction-informative-language]]
=== Informative Language

Some language in the specification is purely informative, intended to give
background or suggestions to implementors or developers.

If an entire chapter or section contains only informative language, its
title will be suffixed with "`(Informative)`".

All NOTEs are implicitly informative.


[[introduction-normative-terminology]]
=== Normative Terminology

Within this specification, the key words *must*, *required*, *should*,
*recommended*, *may*, and *optional* are to be interpreted as described in
https://www.ietf.org/rfc/rfc2119.txt[RFC 2119 - Key words for use in RFCs to
Indicate Requirement Levels] (https://www.ietf.org/rfc/rfc2119.txt).
The additional key word *optionally* is an alternate form of *optional*, for
use where grammatically appropriate.

These key words are highlighted in the specification for clarity.
In text addressing application developers, their use expresses requirements
that apply to application behavior.
In text addressing implementors, their use expresses requirements that apply
to implementations.

In text addressing application developers, the additional key words *can*
and *cannot* are to be interpreted as describing the capabilities of an
application, as follows:

*can*::
This word means that the application is able to perform the action
described.

*cannot*::
This word means that the API and/or the execution environment provide no
mechanism through which the application can express or accomplish the action
described.

These key words are never used in text addressing implementors.

[NOTE]
.Note
==================
There is an important distinction between *cannot* and *must not*, as used
in this Specification.
*Cannot* means something the application literally is unable to express or
accomplish through the API, while *must not* means something that the
application is capable of expressing through the API, but that the
consequences of doing so are undefined: and potentially unrecoverable for
the implementation (see <<fundamentals-validusage>>).
==================

Unless otherwise noted in the section heading, all sections and appendices
in this document are normative.


[[introduction-technical-terminology]]
=== Technical Terminology

The Vulkan Specification makes use of common engineering and graphics terms
such as *Pipeline*, *Shader*, and *Host* to identify and describe Vulkan API
constructs and their attributes, states, and behaviors.
The <<glossary,Glossary>> defines the basic meanings of these terms in the
context of the Specification.
The Specification text provides fuller definitions of the terms and may
elaborate, extend, or clarify the <<glossary,Glossary>> definitions.
When a term defined in the <<glossary,Glossary>> is used in normative
language within the Specification, the definitions within the Specification
govern and supersede any meanings the terms may have in other technical
contexts (i.e. outside the Specification).


[[introduction-normative-references]]
=== Normative References

References to external documents are considered normative references if the
Specification uses any of the normative terms defined in
<<introduction-normative-terminology>> to refer to them or their
requirements, either as a whole or in part.

The following documents are referenced by normative sections of the
specification:

[[ieee-754]]
IEEE.
August, 2008.
_IEEE Standard for Floating-Point Arithmetic_.
IEEE Std 754-2008.
https://dx.doi.org/10.1109/IEEESTD.2008.4610935 .

[[data-format]] Andrew Garrard.
_Khronos Data Format Specification, version 1.3_.
https://www.khronos.org/registry/DataFormat/specs/1.3/dataformat.1.3.html .

[[spirv-extended]] John Kessenich.
_SPIR-V Extended Instructions for GLSL, Version 1.00_ (February 10, 2016).
https://www.khronos.org/registry/spir-v/ .

[[spirv-spec]] John Kessenich, Boaz Ouriel, and Raun Krisch.
_SPIR-V Specification, Version 1.5, Revision 3, Unified_ (April 24, 2020).
https://www.khronos.org/registry/spir-v/ .

[[vulkan-registry]] Jon Leech.
_The Khronos Vulkan API Registry_.
https://www.khronos.org/registry/vulkan/specs/1.2/registry.html .

[[vulkan-styleguide]] Jon Leech and Tobias Hector.
_Vulkan Documentation and Extensions: Procedures and Conventions_.
https://www.khronos.org/registry/vulkan/specs/1.2/styleguide.html .

[[LoaderAndLayerInterface]]
_Vulkan Loader Specification and Architecture Overview_ (August, 2016).
https://github.com/KhronosGroup/Vulkan-Loader/blob/master/loader/LoaderAndLayerInterface.md
.

