Simple DirectMedia Layer

Simple DirectMedia Layer (SDL) is a cross-platform software development library designed to provide a hardware abstraction layer for computer multimedia hardware components. Software developers can use it to write high-performance computer games and other multimedia applications that can run on many operating systems such as Android, iOS, Linux, macOS, and Windows.[4]

Simple DirectMedia Layer
SDL logo
Original author(s)Sam Lantinga
Developer(s)SDL Community
Initial release1998 (1998)
Stable release
2.0.14[1] / 21 December 2020 (2020-12-21)[2]
Repository
Written inC
Operating systemLinux, Windows, macOS 10.4+, iOS 3.1.3+, tvOS,[3] Android 2.3.3+, FreeBSD 8.4+, Haiku
Additionally before v2.0.0 (deprecated versions): AmigaOS, RISC OS[4]
TypeAPI
Licensezlib License
Before 2.0.0:
GNU LGPL[5]
Websitewww.libsdl.org

SDL manages video, audio, input devices, CD-ROM, threads, shared object loading, networking and timers.[6] For 3D graphics, it can handle an OpenGL, Vulkan,[7] Metal, or Direct3D11 (older Direct3D version 9 is also supported) context. A common misconception is that SDL is a game engine, but this is not true. However, the library is suited to building games directly, or is usable indirectly by engines built on top of it.

The library is internally written in C and possibly, depending on the target platform, C++ or Objective-C, and provides the application programming interface in C, with bindings to other languages available.[8] It is free and open-source software subject to the requirements of the zlib License since version 2.0, and with prior versions subject to the GNU Lesser General Public License.[5] Under the zlib License, SDL 2.0 is freely available for static linking in closed-source projects, unlike SDL 1.2.[9] SDL 2.0, released in 2013, was a major departure from previous versions, offering more opportunity for 3D hardware acceleration, but breaking backwards-compatibility.

SDL is extensively used in the industry in both large and small projects. Over 700 games, 180 applications, and 120 demos have been posted on the library website.

History

Sam Lantinga created the library, first releasing it in early 1998, while working for Loki Software. He got the idea while porting a Windows application to Macintosh. He then used SDL to port Doom to BeOS (see Doom source ports). Several other free libraries were developed to work alongside SDL, such as SMPEG and OpenAL. He also founded Galaxy Gameworks in 2008 to help commercially support SDL, although the company plans are currently on hold due to time constraints.[10]

Soon after putting Galaxy Gameworks on hold, Lantinga announced that SDL 1.3 (which would then later become SDL 2.0) would be licensed under the zlib License.[11] Lantinga announced SDL 2.0 on 14 July 2012, at the same time announcing that he was joining Valve, the first version of which was announced the same day he joined the company.[12] Lantinga announced the stable release of SDL 2.0.0 on 13 August 2013.[13]

SDL 2.0 is a major update to the SDL 1.2 codebase with a different, not backwards-compatible[14] API. It replaces several parts of the 1.2 API with more general support for multiple input and output options. Some feature additions include multiple window support, hardware-accelerated 2D graphics, and better Unicode support.[15]

Support for Mir and Wayland was added in SDL 2.0.2[16] and enabled by default in SDL 2.0.4.[17] Version 2.0.4 also provided better support for Android.[18]

Software architecture

SDL is a wrapper around the operating-system-specific functions that the game needs to access. The only purpose of SDL is to provide a common framework for accessing these functions for multiple operating systems (cross-platform).[19] SDL provides support for 2D pixel operations, sound, file access, event handling, timing and threading. It is often used to complement OpenGL by setting up the graphical output and providing mouse and keyboard input, since OpenGL comprises only rendering.

A game using the Simple DirectMedia Layer will not automatically run on every operating system, further adaptations must be applied. These are reduced to the minimum, since SDL also contains a few abstraction APIs for frequent functions offered by an operating system.

The syntax of SDL is function-based: all operations done in SDL are done by passing parameters to subroutines (functions). Special structures are also used to store the specific information SDL needs to handle. SDL functions are categorized under several different subsystems.

Subsystems

SDL is divided into several subsystems:[20]

Basics
Initialization and Shutdown, Configuration Variables, Error Handling, Log Handling
Video
Display and Window Management, surface functions, rendering acceleration, etc.
Input Events
Event handling, Support for Keyboard, Mouse, Joystick and Game controller
Force Feedback
SDL_haptic.h implements support for "Force Feedback"
Audio
SDL_audio.h implements Audio Device Management, Playing and Recording
Threads
multi-threading: Thread Management, Thread Synchronization Primitives, Atomic Operations
Timers
Timer Support
File Abstraction
Filesystem Paths, File I/O Abstraction
Shared Object Support
Shared Object Loading and Function Lookup
Platform and CPU Information
Platform Detection, CPU Feature Detection, Byte Order and Byte Swapping, Bit Manipulation
Power Management
Power Management Status
Additional
Platform-specific functionality

Besides this basic, low-level support, there also are a few separate official libraries that provide some more functions. These comprise the "standard library", and are provided on the official website and included in the official documentation:

  • SDL_image — support for multiple image formats[21]
  • SDL_mixer — complex audio functions, mainly for sound mixing[22]
  • SDL_net — networking support[23]
  • SDL_ttf — TrueType font rendering support[24]
  • SDL_rtf — simple Rich Text Format rendering[25]

Other, non-standard libraries also exist. For example: SDL_Collide on Sourceforge created by Amir Taaki.

Language bindings

The SDL 2.0 library has language bindings for:

Supported back-ends
Abstraction layers of several SDL platforms

Because of the way SDL is designed, much of its source code is split into separate modules for each operating system, to make calls to the underlying system. When SDL is compiled, the appropriate modules are selected for the target system. The following back-ends are available:[4]

SDL 1.2 has support for RISC OS (dropped in 2.0).

An unofficial Sixel back-end is available for SDL 1.2.[43]

The Rockbox MP3 player firmware also distributes a version of SDL 1.2, which is used to run games such as Quake.[44]

Reception and adoption
Workshop on SDL, University of Cádiz

Over the years SDL was used for many commercial and non-commercial video game projects. For instance, MobyGames listed 120 games using SDL in 2013,[45] and the SDL website itself listed around 700 games in 2012.[46] Important commercial examples are Angry Birds[47] and Unreal Tournament; ones from the open-source domain are OpenTTD,[48] The Battle for Wesnoth[49] or Freeciv.[50]

The cross-platform game releases of the popular Humble Indie Bundles for Linux, Mac and Android are often SDL based.

SDL is also often used for later ports on new platforms with legacy code. For instance, the PC game Homeworld was ported to the Pandora handheld[51] and Jagged Alliance 2 for Android[52] via SDL.

Also, several non video game programs use SDL; examples are the emulators, such as DOSBox, FUSE ZX Spectrum emulator and VisualBoyAdvance.

There were several books written for development with SDL (see further readings).

SDL is used in university courses teaching multimedia and computer science, for instance, in a workshop about game programming using libSDL at the University of Cadiz in 2010, or a Game Design discipline at UTFPR (Ponta Grossa campus) in 2015.

Video game examples using SDL
Main article: List of games using SDL

See also

References
  1. "Simple DirectMedia Layer - SDL version 2.0.14 (stable)". Libsdl.org. Retrieved 23 December 2020.
  2. "Index of /release". Libsdl.org. Retrieved 23 December 2020.
  3. "Oh look, we'll have official tvOS support in SDL 2.0.5, for people that want their SDL-based games on Apple TV!". 15 September 2016.
  4. "a list of the platforms SDL supports". Libsdl.org. Archived from the original on 1 April 2016. Retrieved 9 April 2016.
  5. "SDL license". Retrieved 3 March 2014.
  6. "SDL official website". Libsdl.org. Retrieved 19 March 2010.
  7. "CategoryVulkan - SDL Wiki'". wiki.libsdl.org. Retrieved 5 May 2019.
  8. "SDL Language Bindings". libsdl.org. Simple DirectMedia Layer. Retrieved 13 August 2014.
  9. "Licensing the Simple DirectMedia Layer library". Retrieved 30 January 2012.
  10. "Exploring the Galaxy". 6 April 2011. Retrieved 30 January 2012.
  11. SDL 1.3 to be zLib Licensed, SDL Mailing List, 7 April 2011
  12. "SDL 2.0 Is Coming Very Soon With New Features". Retrieved 17 August 2012.
  13. Announcing SDL 2.0.0, SDL Mailing List, 13 August 2013
  14. MigrationGuide - SDL Wiki'. Wiki.libsdl.org (21 November 2013). Retrieved on 2013-12-08.
  15. "SDL 1.3 Roadmap". 14 June 2011. Retrieved 25 July 2011.
  16. Sneddon, Joey-Elijah (5 February 2014). "Some of Linux's Most Popular Games Will Run Natively On Mir". Retrieved 19 March 2014.
  17. Lantinga, Sam (2 January 2016). "SDL 2.0.4 Changelog". Retrieved 6 January 2016.
  18. https://wiki.libsdl.org/SDL_SysWMinfo
  19. "Introduction to SDL". Retrieved 3 March 2014.
  20. https://wiki.libsdl.org/APIByCategory
  21. "SDL_image 2.0". libsdl.org. Retrieved 19 July 2014.
  22. "SDL_mixer 2.0". libsdl.org. Retrieved 19 July 2014.
  23. "SDL_net 2.0". libsdl.org. Retrieved 19 July 2014.
  24. "SDL_ttf 2.0". libsdl.org. Retrieved 19 July 2014.
  25. "SDL_rtf 0.1". libsdl.org. Retrieved 19 July 2014.
  26. "f03sdl2". GitHub. Retrieved 28 October 2019.
  27. Robison, Arch D. (9 November 2015). "Go + Julia + Fourier = Open Source Frequon Invaders". software.intel.com. Retrieved 2 August 2019.
  28. "SDL on Hackage".
  29. "SDL2 on Hackage".
  30. Bieler, Jonathan (30 July 2020). "jonathanBieler/SimpleDirectMediaLayer.jl". Retrieved 8 August 2020.
  31. SquidSinker (2 August 2020). "Example games for GameZero.jl". Retrieved 8 August 2020.
  32. Daly, Nathan (31 July 2019). "Example game written in julia using SDL2". Retrieved 2 August 2019.
  33. "PerlGameDev/SDL". GitHub. Retrieved 20 February 2019.
  34. "PHP-SDL". GitHub. Retrieved 28 October 2019.
  35. "SDL2::Raw". modules.raku.org. Retrieved 15 May 2020.
  36. "cl-sdl2". GitHub. Retrieved 23 November 2017.
  37. "WhatsNew.txt". Retrieved 28 September 2020.
  38. "[Commits] SDL: Enable building the Metal renderer by default, and weak lin..." 7 December 2017.
  39. "SDL: README-platforms.txt@3e2f230a6d62". Hg.libsdl.org. libsdl.org. Archived from the original on 15 December 2013. Retrieved 8 December 2013.
  40. "Using OpenGL With SDL". Retrieved 9 July 2015.
  41. "SDL and Wayland".
  42. Larabel, Michael (30 September 2013). "Raspberry Pi Support Added To SDL2 Library".
  43. "SDL 1.2 Sixel". Retrieved 9 April 2016.
  44. "SDLPluginPort". Retrieved 11 August 2019.
  45. "Middleware: SDL Group Description". MobyGames. 27 September 2013. Retrieved 18 May 2012. Games that use the very portable Simple DirectMedia Layer.
  46. "Games". libsdl.org. 18 May 2012. Archived from the original on 29 June 2010. Retrieved 18 May 2012.
  47. "SDL Testimonials". Galaxygameworks.com. Archived from the original on 16 July 2011. Retrieved 1 February 2012.
  48. "Development". OpenTTD. Retrieved 19 March 2010.
  49. "CompilingWesnoth". Wesnoth. 27 February 2010. Retrieved 19 March 2010.
  50. "SDLClient - Freeciv.org". Freeciv.wikia.com. Retrieved 19 March 2010.
  51. may88 (23 June 2011). "Game of the Week #3 – Homeworld SDL". pandorapress.net. Retrieved 8 May 2012. [...] released port of HomeworldSDL. Forum member Edglex enables your Pandora to experience the excellent work done by the guys at HomeworldSDL.
  52. JA2 Stracciatella Feedback » Jagged Alliance 2 Android Stracciatella Port RC2 Release - please test Archived 23 October 2012 at the Wayback Machine on the Bear's Pit Forum, 3 October 2011
  53. "Features · fifengine/fifengine Wiki · GitHub". Retrieved 9 March 2015.
  54. "FAQ Hedgewars". hedgewars.org. Retrieved 3 October 2014. ... SDL >= 1.2.5 ...
  55. "Development Details". scorched3d.co.uk. Archived from the original on 6 October 2014. Retrieved 3 October 2014. ... Simple DirectMedia Layer - SDL for cross platform game windowing ...
  56. "Roadmap - Wesnoth". www.wesnoth.org. Retrieved 9 March 2015.
  57. "Secret Maryo Chronicles". sourceforge.net. Retrieved 3 October 2014. ... based on SDL ...
  58. "Frozenbyte Support". trine2.com. Retrieved 1 September 2020.

Further reading
  • Alberto García Serrano: Programación de videojuegos en SDL, Ediversitas, ISBN 84-95836-08-4 (Spanish)
  • Ernest Pazera: Focus On SDL, Muska & Lipman/Premier-Trade, ISBN 1-59200-030-4
  • Ron Penton: Data Structures for Game Programmers, Muska & Lipman/Premier-Trade, ISBN 1-931841-94-2 (game programming examples with SDL)
  • John R. Hall: Programming Linux Games, No Starch, ISBN 1-886411-49-2 (First SDL book, by Loki Games, archived online version: PDF at the Wayback Machine (archived 22 January 2003), LaTex sources at the Wayback Machine (archived 14 February 2003))
  • SDL Game Development by Shaun Mitchell
  • Game Development with SDL 2.0 on YouTube – video from 11 February 2014 by Ryan C. Gordon
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