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
2 inequation.org2 inequation.org
● 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
5 inequation.org5 inequation.org
● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

6. What is SDL?What is SDL?
6 inequation.org6 inequation.org
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
12 inequation.org12 inequation.org
● Who is this guy?
● Introduction to SDL
● Event pump
● New features of SDL 2.0
● Questions

13. Event pumpEvent pump
13 inequation.org13 inequation.org
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
16 inequation.org16 inequation.org
● 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
17 inequation.org17 inequation.org
● 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
18 inequation.org18 inequation.org
● 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
19 inequation.org19 inequation.org
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
21 inequation.org21 inequation.org
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
22 inequation.org22 inequation.org
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*
23 inequation.org23 inequation.org
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*
24 inequation.org24 inequation.org
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*
25 inequation.org25 inequation.org
● 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