cross-platform game engine development with sdl 2.0

inequation.orginequation.org

WGK 2013 · September 7th, 2013WGK 2013 · September 7th, 2013

Cross-platform game engine development with SDL 2.0

Leszek GodlewskiFreelance [email protected]

AgendaAgenda

2 inequation.org2 inequation.org

● Who is this guy?

● Introduction to SDL

● Event pump

● New features of SDL 2.0

● Questions

Who is this guy?Who is this guy?


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

http://www.inequation.org/

http://www.thefarm51.com/

Who is this guy?Who is this guy?


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

http://github.com/inequation/

AgendaAgenda




● Event pump


● Questions

What is SDL?What is SDL?


Simple DirectMedia LayerThe 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!

Benefits of SDLBenefits of SDL


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!



All platform details hidden away under a unified interface!

(truly one codebase shared by all of them → write once, compile anywhere)



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;}

MonoGame-SDL2MonoGame-SDL2


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

http://www.flibitijibibo.com/

http://twitter.com/flibitijibibo

http://github.com/flibitijibibo/MonoGame

Sample SDL game: AC-130Sample SDL game: AC-130


AgendaAgenda




● Event pump


● Questions

Event pumpEvent pump


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()

Event pumpEvent pump


● 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!

Sample SDL game: AC-130Sample SDL game: AC-130


<AC-130 main loop breakdown>

github.com/inequation/ac130

http://github.com/inequation/ac130

AgendaAgenda




● Event pump


● Questions

Current state of SDL 2Current state of SDL 2


● 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

What's new in SDL 2What's new in SDL 2


● 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

OpenGL context sharingOpenGL context sharing


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.)!



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);



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)

Full-screen quirksFull-screen quirks


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!

Game controller API: SDL_GameController*Game controller API: SDL_GameController*


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

Game controller API: SDL_GameController*Game controller API: SDL_GameController*


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()

Haptic feedback: SDL_Haptic*Haptic feedback: SDL_Haptic*


● 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

TakeawayTakeaway


● 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.orgbugzilla.libsdl.org

http://www.libsdl.org/

https://bugzilla.libsdl.org/


Questions?

[email protected]



Thank you!

[email protected]@TheIneQuation


http://www.inequation.org/

http://twitter.com/TheIneQuation

cross-platform game engine development with sdl 2.0

Technology

null sdl

accelerated sdl

callbacks sdl

destroytexturetex sdl

destroyrendererren sdl

delay2000 sdl

freesurfacebmp sdl

destroywindowwin sdl