Linux as a gaming platform - Errata
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This document is a series of errata and clarifications from a previous talk on game development for Linux. It addresses shortcomings in SDL for threaded rendering and audio capabilities, and clarifies that OpenGL context sharing is possible in SDL2. It also recommends using SDL2's joystick and game controller APIs rather than low-level kernel interfaces. Placement of game files on Linux systems and XDG standard directories for configuration and user data are explained. The document concludes by thanking readers and suggesting that an upcoming game may also come to Linux.
Linux as a gaming platform - Errata
- 1. Linux as a gaming platform Ideology aside 14-07-2013 Leszek Godlewski Generalist Programmer leszek.godlewski@thefarm51.com www.thefarm51.com ERRATA
- 2. 2 I stand corrected! www.thefarm51.com On April 19, 2013 I gave a talk on game development for Linux at the Digital Dragons European Games Festival. In it, I made a couple of mistakes and omissions that I hereby would like to correct. 2
- 3. 3 What if SDL doesn't cut it? www.thefarm51.com Despite its awesomeness, SDL has its shortcomings ● No explicit GLX/WGL context data sharing and no direct context access → no threaded rendering ☹ (hit this corner while porting Painkiller HD) ● No 3D positioning or DSP support in the stock SDL audio subsystem - Partially remedied by SDL_mixer But we need those! Now what?! Original slide 24
- 4. 4 What if SDL doesn't cut it? www.thefarm51.com Despite its awesomeness, SDL has its shortcomings ● No explicit GLX/WGL context data sharing and no direct context access → no threaded rendering ☹ (hit this corner while porting Painkiller HD) ● No 3D positioning or DSP support in the stock SDL audio subsystem - Partially remedied by SDL_mixer But we need those! Now what?! Original slide 24
- 5. 5 OpenGL context sharing in SDL2 www.thefarm51.com5 It actually is possible! ● Just undocumented... ☹ Only mention I could find 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.)!
- 6. 6 OpenGL context sharing in SDL2 www.thefarm51.com I re-read the Valve slides about porting their games to Linux, and noticed their renderer is multithreaded. I knew from elsewhere they are using SDL2, so I thought I should check the source code, not just the SDL2 documentation. As soon as I found out about my mistake, I rewrote the Painkiller Hell & Damnation client code to use SDL2, too. ☺ 6
- 7. 7 Joystick/gamepad API www.thefarm51.com ● Not part of X11 input event framework ● Kernel block devices - Created as /dev/input/js* - Hotplug events via libudev (also in Steam Linux Runtime) - Handled via open() and ioctl() - Detailed documentation in the kernel http://kernel.org/doc/Documentation/input/joystick-api.txt Original slide 28 W ell, yeah, W ell, yeah, but... but...
- 8. 8 SDL2 joystick and controller APIs www.thefarm51.com8 Why hurt yourself with the low-level kernel joystick interface and libudev?
- 9. 9 SDL2 joystick and controller APIs www.thefarm51.com9 Joystick API ● Support for axes, buttons, hats and trackballs ● State polling or events ● Hotplugging ● Force feedback via the haptic SDL2 subsystem
- 10. 1 0 SDL2 joystick and controller APIs www.thefarm51.com10 Game controller API ● Built on top of the joystick API ● Maps any joystick/gamepad input to a layout modelled after the Xbox 360 controller ● Built by Valve with Steam Big Picture in mind ● Bindings may be imported/exported via strings ● Popular controllers have built-in mappings ● API very similar to the regular joystick API, but buttons and axes are identified by enumerations ● SDL_GameControllerAxis ● SDL_GameControllerButton
- 11. 1 1 Where do I put the files? www.thefarm51.com ● Windows - Game data and binaries: C:Program Files - User data: %APPDATA%, Documents... - AoS-like organization ● Linux (conventional) - Game binaries: /usr/bin/, /usr/games/ - Game data: /usr/share/games/ - User data: $HOME/.config/ ($XDG_CONFIG_HOME environment variable) - SoA-like organization - Filesystem Hierarchy Standard Original slide 42 W ell, yeah, W ell, yeah, but... but...
- 12. 1 2 Where do I put the files? www.thefarm51.com ● FHS mainly concerns distro packages ● Proprietary software often installs into /opt/<package name>/ (“Add-on application software packages”) ● Proprietary software also often installs “wherever” ● Steam games live in ~/.steam/steam/SteamApps/ ● Just put game data and binaries in one place, and save user data to ~/.config/ Original slide 43 W ell, yeah, W ell, yeah, but... but...
- 13. 1 3 $XDG_CONFIG_HOME and friends www.thefarm51.com13 ● Actually, $XDG_CONFIG_HOME (a.k.a. $HOME/.config) is a for textual configuration files ● User data, which is a more accurate description for savegames, DLC etc., goes into $XDG_DATA_HOME (defaults to $HOME/.local/share) ● All of this is regulated by a FreeDesktop.org standard: http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
- 14. 1 4 Summary www.thefarm51.com14 That's all, folks, for now. Sorry for not getting this errata out earlier – at The Farm 51 we're very busy finishing Deadfall Adventures. What do you think, should it be coming to Linux as well? ☺ If you spot any more mistakes, feel free to shoot me an email. Many thanks to Michael Larabel at Phoronix for blowing up my Slideshare with all the traffic from their news story. ☺ Keep on playing, Linux gamers!
- 15. 1 5 Thank you! Like us on Facebook! http://www.facebook.com/farm51 http://www.facebook.com/deadfalladventures http://www.facebook.com/PainkillerGame leszek.godlewski@thefarm51.com www.thefarm51.com