Lecture from the WGK 2013 game development conference The SDL library (Simple DirectMedia Layer) - known as "the open source response to DirectX" - lets you forget about all the boilerplate in game development on platforms ranging from Windows, through Linux and Mac OS X, to iOS and Android. While still in active development, version 2.0 of SDL provides new and improved functionality, including touch input and force feedback support. It also ships with the Steam Linux Library. This lecture provides an overview of the library's capabilities and some useful tricks.

1. inequation.orginequation.org
WGK 2013 · September 7th, 2013WGK 2013 · September 7th, 2013
Cross-platform game engine
development with SDL 2.0
Leszek Godlewski
Freelance Programmer
lg@inequation.org

2. AgendaAgenda
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● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

3. Who is this guy?Who is this guy?
3 inequation.org3 inequation.org
Freelance Programmer
(Sep 2013 – onwards)
● inequation.org
● Unannounced project
Generalist Programmer,
The Farm 51
(Mar 2010 – Aug 2013)
● thefarm51.com
● Painkiller Hell & Damnation
(2012-2013; Win/Linux/X360/PS3)
● Deadfall Adventures (2011-2013;
Win/X360)
● A few unannounced projects

4. Who is this guy?Who is this guy?
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Cross-platform work
( de facto – Linux)→
● github.com/inequation
● Toy projects, personal utilities,
university stuff
● Games as well!
● AC-130
● Crystal Space
● idTech 3-based games
● Painkiller Hell & Damnation
● Linux as preferred OS for 7+ years
● Former open-source evangelist
● Not anymore – lost interest

5. AgendaAgenda
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● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

6. What is SDL?What is SDL?
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Simple DirectMedia Layer
The cross-platform, open-source „DirectX”
● Written by Sam Lantinga (ex-Loki, ex-Blizzard,
currently Valve), Ryan Gordon (legendary porter) et al.
● Provides:
● API in C with mappings to other languages
● Timers and threads
● Thread-safe input and events (incl. Unicode and IME)
● Polled and event-based APIs (incl. filtering)
● Window management (incl. OpenGL [ES] contexts)
● Audio (very barebone)
● Accelerated 2D graphics (simple drawing, blitting)
● More!

7. Benefits of SDLBenefits of SDL
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Many supported platforms
● Windows XP+
● Linux 2.6+
● Mac OS X 10.5+
● Android 2.3.3+
● iOS 4.0.1+
● Many more: Free/Open/NetBSD, Solaris, Playstation Portable,
Haiku, Pandora...
Yup,
mobiles!

8. Benefits of SDLBenefits of SDL
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All platform details hidden away under a
unified interface!
(truly one codebase shared by all of them
→ write once, compile anywhere)

9. Benefits of SDLBenefits of SDL
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Extremely simple – goodbye, boilerplate!
int main(int argc, char** argv) {
if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
return 1;
SDL_Window *win = SDL_CreateWindow("Hello World!",
100, 100, 640, 480, SDL_WINDOW_SHOWN);
SDL_Renderer *ren = SDL_CreateRenderer(win, -1,
SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
SDL_Surface *bmp = SDL_LoadBMP("hello.bmp");
SDL_Texture *tex = SDL_CreateTextureFromSurface(ren, bmp);
SDL_FreeSurface(bmp);
SDL_RenderClear(ren);
SDL_RenderCopy(ren, tex, NULL, NULL);
SDL_RenderPresent(ren);
SDL_Delay(2000);
SDL_DestroyTexture(tex);
SDL_DestroyRenderer(ren);
SDL_DestroyWindow(win);
SDL_Quit();
return 0;
}

10. MonoGame-SDL2MonoGame-SDL2
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Hey indies!
● MonoGame: an XNA implementation on top of Mono
● MG-SDL2: backend for MonoGame by Ethan Lee
(Twitter: @flibitijibibo)
● Shipped and WIP games:
● Capsized
● FEZ
● Gateways
http://github.com/flibitijibibo/MonoGame

11. Sample SDL game: AC-130Sample SDL game: AC-130
11 inequation.org11 inequation.org

12. AgendaAgenda
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● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

13. Event pumpEvent pump
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SDL encapsulates hardware, system, window
management and input events
● SDL_QUIT, SDL_APP_TERMINATING, SDL_APP_LOWMEMORY, SDL_APP_WILLENTERBACKGROUND,
SDL_APP_DIDENTERBACKGROUND, SDL_APP_WILLENTERFOREGROUND,
SDL_APP_DIDENTERFOREGROUND, SDL_WINDOWEVENT, SDL_SYSWMEVENT, SDL_KEYDOWN,
SDL_KEYUP, SDL_TEXTEDITING, SDL_TEXTINPUT, SDL_MOUSEMOTION, SDL_MOUSEBUTTONDOWN,
SDL_MOUSEBUTTONUP, SDL_MOUSEWHEEL, SDL_JOYAXISMOTION, SDL_JOYBALLMOTION,
SDL_JOYHATMOTION, SDL_JOYBUTTONDOWN, SDL_JOYBUTTONUP, SDL_JOYDEVICEADDED,
SDL_JOYDEVICEREMOVED, SDL_CONTROLLERAXISMOTION, SDL_CONTROLLERBUTTONDOWN,
SDL_CONTROLLERBUTTONUP, SDL_CONTROLLERDEVICEADDED, SDL_CONTROLLERDEVICEREMOVED,
SDL_CONTROLLERDEVICEREMAPPED, SDL_FINGERDOWN, SDL_FINGERUP, SDL_FINGERMOTION,
SDL_DOLLARGESTURE, SDL_DOLLARRECORD, SDL_MULTIGESTURE, SDL_CLIPBOARDUPDATE,
SDL_DROPFILE, SDL_USEREVENT
● SDL_PeepEvents(), SDL_PollEvents(),
SDL_WaitEvent()...
● Filtering: simple, by type (SDL_EventState()) or
complex with callbacks (SDL_EventFilter)
● Custom user events - SDL_RegisterEvents()

14. Event pumpEvent pump
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● Probably the single coolest feature!
● One switch in a loop takes care of almost everything
● Typical SDL application structure:
● Subsystem initialization
● Event pump
● Cleanup
● That's it!

15. Sample SDL game: AC-130Sample SDL game: AC-130
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<AC-130 main loop breakdown>
github.com/inequation/ac130

16. AgendaAgenda
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● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

17. Current state of SDL 2Current state of SDL 2
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● First stable release, 2.0.0, announced August 11th
● Present in the Steam Linux Runtime since early RCs
● Valve games and others rely on it
● Documentation is slightly outdated
● Ongoing effort, gaps being quickly filled
● You might be misled to believe a feature is missing...
● When in doubt, read header file comments or
generate your own docs

18. What's new in SDL 2What's new in SDL 2
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● OpenGL 3+ support
● Incl. context sharing (finally!)
● OpenGL ES support
● Haptic (force) feedback
● Game controller API
● Android and iOS support
● Touch input with gestures
● Support for multiple displays, windows, audio devices
● IME and proper Unicode support
● Pluggable 2D renderer backends
● Portable atomic operations
● Power management
● Rudimentary UI (message boxes etc.)
● Clipboard & drag-and-drop support

19. OpenGL context sharingOpenGL context sharing
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Finally – yay for multithreaded/multi-window
rendering! ☺
●
Undocumented... ☹ FIXED as of August 11th
● Only mention in Google is the May 2012 commit that
introduces the feature
● Needs an SDL-OpenGL attribute set before window
creation:
SDL_GL_SetAttribute(
SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1);
● Voila - all contexts created from now on with
SDL_GL_CreateContext() will share data with the
currently bound context (buffers, shaders etc.)!

20. OpenGL context sharingOpenGL context sharing
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Gotcha: pre-RC4 SDL2 keeps a global
reference to the current window/GL context
pair
● Care must be taken when unbinding contexts (e.g.
when killing worker threads)!
// …
SDL_GL_MakeCurrent(NULL, NULL);
// most SDL_GL_* calls made on any thread
// will crash now :(
● Solution: simply bind back to the main window and
context instead of unbinding
SDL_GL_MakeCurrent(MainWindow, MainGLCtx);

21. OpenGL context sharingOpenGL context sharing
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Gotcha: pre-RC4 SDL2 keeps a global
reference to the current window/GL context
pair
RC4 and newer (incl. 2.0.0 stable) – nothing to worry
about ☺
● Some distros still ship <= RC4
● Ship your own or use Steam Linux Runtime
(fixed on 11 Jul 2013, rev. 50211a1fd557)

22. Full-screen quirksFull-screen quirks
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Gotcha: full-screen in Linux is hacky ☹
● X11 doesn't really support „true” full-screen windows
● Actually just a decoration-less window
● SDL_WINDOW_FULLSCREEN uses an XRandR hack
● Change display mode while maintaining desktop size
● Crop the „viewport”
● Side effect: „viewport” follows mouse and may scroll
away from app window... Bad! ☹
● SDL_WINDOW_FULLSCREEN_DESKTOP simply creates a
desktop-sized window, no XRandR magic
● Render to offscreen buffer (FBO), then blit with scaling
● This is what Valve does!

23. Game controller API: SDL_GameController*Game controller API: SDL_GameController*
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Unified gamepad/joystick handling
● Layout modelled after the Xbox 360 controller
● Built by Valve with Steam Big Picture in mind
● Button/axis mapping support for other controllers
● Kind of a built-in equivalent to Xpadder
● Bindings may be imported/exported via strings
● Popular controllers have built-in mappings
● Hotplug support – yay!
● May be polled for state or handled with events
● API very similar to the regular joystick API, but buttons
and axes are identified by enumerations instead
● SDL_GameControllerAxis
● SDL_GameControllerButton

24. Game controller API: SDL_GameController*Game controller API: SDL_GameController*
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Gotcha: joystick/game controller API interop
● GC API is implemented on top of the SDL joystick API
● SDL GC subsystem initialization implies joystick
subsystem initialization
● Regular joystick events are issued for GCs as well!
● This means double events for the axes, buttons, even
hotplugs!
● Don't need joystick hats, arbitrary axes etc.? Just filter
out joystick events altogether
● Otherwise you can identify the device type with
SDL_IsGameController()

25. Haptic feedback: SDL_Haptic*Haptic feedback: SDL_Haptic*
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● Powerful API with more than just rumbles
● Remember arcade racing machines that blocked the
steering wheel and pedals?
● Haptic devices may be stand-alone (e.g. rumble motors
in mobile devices) or derived from joysticks with
SDL_HapticOpenFromJoystick()
● Simplified API for rumbles

26. TakeawayTakeaway
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● Battle-proven low-level abstraction layer
● Ships with the Steam Linux Runtime
● Support for many platforms, including Windows, Linux,
Mac, mobiles and some handheld consoles
● Provides a universal event pump
● Integrates well with OpenGL
● Exposes game controllers and force feedback
● Open-source!
libsdl.org
bugzilla.libsdl.org

27. inequation.orginequation.org
Questions?
lg@inequation.org
WGK 2013 · September 7th, 2013WGK 2013 · September 7th, 2013

28. inequation.orginequation.org
Thank you!
inequation.org
lg@inequation.org
@TheIneQuation
WGK 2013 · September 7th, 2013WGK 2013 · September 7th, 2013