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Simple DirectMedia Layer (SDL) is a cross-platform, free and open source multimedia library written in C that presents a simple interface to various platforms' graphics, sound, and input devices. It is widely used due to its simplicity. Over 700 games, 180 applications, and 120 demos have been posted on its website.
SDL has the word "layer" in its title because it is actually a wrapper around operating-system-specific functions. The main purpose of SDL is to provide a common framework for accessing these functions. For further functionality beyond this goal, many libraries have been created to work on top of SDL.
Software developers use it to write computer games and other multimedia applications that can run on many operating systems: Android, iOS, Linux, Mac OS X, Windows and other (unofficially supported) platforms.[3] It manages video, events, digital audio, CD-ROM, threads, shared object loading, networking and timers.
SDL acts as a cross-platform wrapper, providing 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, which are not supported by OpenGL.
The library is divided into several subsystems, namely the video (handles both surface functions and OpenGL), audio, CD-ROM, joystick, and timer subsystems. 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
SDL_mixer — complex audio functions, mainly for sound mixing
SDL_net — networking support
SDL_ttf — TrueType font rendering support
SDL_rtf — simple Rich Text Format rendering
Other, non-standard libraries also exist. For example: SDL_Collide on Sourceforge created by Amir Taaki.
The SDL library has language bindings for many programming languages, from the popular (C, C++, Pascal, Perl, Python (via Pygame), etc.) to the less known languages such as Ch (via ChSDL), Euphoria and Pliant. This makes SDL a commonly used open source library for many multimedia applications.
History
Workshop on SDL, University of Cádiz
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.
Oolite, a 3D space game
SDL 2.0 is a major update to the SDL 1.2 codebase with a different, not backwards-compatible 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.
SDL 2.0 is zlib-licensed, and therefore freely available for static linking in commercial closed-source projects, unlike SDL 1.2. The same day Sam Lantinga announced that he will be joining Valve Software, he also announced that "it's time to unleash SDL 2.0 on the masses".
Ports
Abstraction layers of several SDL platforms
Because of the way SDL is designed, much of the source code is split into separate modules for each operating system, to make calls to the underlying system. When SDL is compiled, the correct modules are selected for the target system.
On Microsoft Windows, SDL uses a GDI backend by default. A DirectX backend is also available. Older versions of SDL used DirectX 5, but SDL 1.2 (the current stable release) requires DirectX 7 by default. Sam Lantinga has stated that he plans to use DirectX 8 in future SDL releases.
On X Window System platforms, including Linux and OpenVMS, SDL uses Xlib to communicate with the X11 system for graphics and events.
On Mac OS X, SDL uses Quartz.
Syntax and subsystems
The syntax of SDL is function-based: all operations done in SDL are done by passing parameters to functions. Special structures are also used to store the specific information SDL needs to handle. There are a few different subsystems SDL categorizes its functions under:
The video, events and threads subsystem: this provides functions for video, multi-threading, and event handling
The audio subsystem: this provides functions for audio
The time subsystem
The joystick subsystem
The CD-ROM subsystem
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Wrapper library - From Wikipedia
In computer programming, a library is a collection of subroutines or classes used to develop software. Libraries expose interfaces which clients of the library use to execute library routines. Wrapper libraries (or library wrappers) consist of a thin layer of code which translates a library's existing interface into a compatible interface.
This is done for several reasons:
To refine a poorly designed or complicated interface.
Allow code to work together which otherwise cannot (e.g. Incompatible data formats).
Enable cross language and/or runtime interoperability.
Wrapper libraries are implemented using the Adapter, Façade, and to a lesser extent, Proxy design patterns.
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