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Simple Directmedia Layer or SDL is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. It is used by video playback software, emulators, and popular games

For general information and documentation about SDL visit the SDL homepage. This page is going to explain how to use SDL with Free Pascal, where to obtain the Pascal headers etc. More information is available at the libsdl-wiki.

Obtaining FPC headers for SDL

After installing the SDL library itself on your system you'll need Pascal headers to be able to use SDL with FPC. Since version 2.2.2, most SDL units are included with FPC itself. You can of course also download them from JEDI-SDL in case you need some bug fix or a unit not in the version shipped with FPC.

SDL headers from JEDI-SDL

See JEDI-SDL Home Page.

You can download JEDI-SDLv1.0 Beta..

You can also download and browse current CVS sources, see JEDI-SDL SourceForge CVS for instructions. In short, just do

  cvs -d:pserver:anonymous@jedi-sdl.cvs.sourceforge.net:/cvsroot/jedi-sdl login 

(when prompted for a password, simply press the Enter key)

  cvs -z3 -d:pserver:anonymous@jedi-sdl.cvs.sourceforge.net:/cvsroot/jedi-sdl co JEDI-SDLv1.0

After you downloaded (and eventually unpacked) JEDI-SDL sources, you want to be able to use these units in your programs. For the simplest scenario, just add the following lines to your fpc.cfg file:


(where <jedi-sdl-path> is the path where you placed jedi-sdl sources).

Alternatively, you can copy all *.pas and *.inc files from these directories to one chosen directory, and add only this chosen directory to your fpc.cfg.

To test that everything works, you can compile and run one of numerous demo programs included, e.g.

 cd <jedi-sdl-path>/JEDI-SDLv1.0/SDLSpriteEngine/Demos/Oxygene/
 fpc -Sd Oxygene.dpr

Note that all jedi-sdl code should be compiled in Delphi-compatible mode. Most jedi-sdl units include jedi-sdl.inc that already has the line {$mode delphi} added, but some example programs don't include jedi-sdl.inc. So be sure to compile them with -Sd command-line option (or add {$mode delphi} directive).

SDL headers from Free Pascal SVN (deprecated)

The code can be downloaded with:

svn co http://svn.freepascal.org/svn/fpcprojects/contrib/sdl/ fpc-sdl

Tips and tricks

SDL_mixer library

When using SDL_mixer, the call to Mix_OpenAudio MUST happen before the call to SDL_SetVideoMode, otherwise you will get a (sometimes loud) audible pop.

SMPEG library

If you use SDL_mixer you'll notice that it's dependent on smpeg library. For modern Linux distros this is not a problem because smpeg is distributed with them, but it can be troublesome eg for FreeBSD and Windows:

Alternatively, you can simply modify the source of SDL_mixer.pas: remove smpeg from it's uses clause and comment out one line in the sources mentioning mp3s (it's a case near the end). Remember that you will also need to have SDL_mixer dll/so that is not linked to smpeg -- otherwise SDL_mixer library will depend on smpeg anyway.

macOS specific issues

SDL Framework and SDL libraries

On macOS, SDL uses Cocoa to setup the drawing window and to handle all events (such as keypresses). This is done using a small piece of code that is automatically called when the program starts up, and which subsequently calls a function with the name SDLmain. More information is available at http://www.libsdl.org/faq.php?action=listentries&category=7#55

There are however two different ways to package/distribute SDL for macOS, and depending on which version you use, the procedure to get this startup code into your program is slightly different.

The framework version

This the version that you get when you download the macOS version of SDL from libsdl.org. In this case, the startup code is only available in source form. It is located on the installation disk image, in the folder devel-lite. After copying the SDL.framework from the disk image to /Library/Frameworks and copying the devel-lite folder anywhere on your hard drive (e.g., in your home directory), you can compile it into libSDLMain.a by opening a Terminal session, navigating to the copied devel-lite folder, and executing the following commands:

gcc -c -o SDLMain.o SDLMain.m -I /Library/Frameworks/SDL.framework/Headers
ar r libSDLMain.a SDLMain.o
ranlib libSDLMain.a

You can then move the generated libSDLMain.a librray anywhere you want. To make sure the linker can find it when you compile SDL applications, pass the -Fl/full/path/to/folder/containing/libSDLMain.a command line parameter to the compiler.

The Unix library version

There is also a "classic Unix" version of SDL for macOS (no framework, just a bunch of separate libraries), which you get if you compile SDL from sources, or if you install SDL using Fink or MacPorts. In this case, libSDLmain.a is already included in a compiled form. You just have to use the compiler's -Fl parameter, as explained in the previous section, to make sure that the linker can find this library.

For FPC 2.2.2 and later

The SDL unit included with FPC includes all necessary framework, library and main procedure name renaming statements, so you no longer have to do anything special. Just add the sdl unit to your program and everything will be taken care of. However, the remarks about libSDLMain in the above section still hold (libSDLMain.a is required by the SDL unit included with FPC).

Note that if you use the original units as distributed by the JEDI team, you may still need to follow the instructions in the section below.

For FPC 2.0.2 to 2.2.0

With fpc 2.0.2 to 2.2.0, and possibly also when using the original SDL units as distributed by the JEDI team, you have to use the -XMSDL_main command line option and tell the linker to include some frameworks:

1) install sdl, for example using fink.

2) Add the following to your program:

{$linklib gcc}
{$linklib SDLmain}
uses sdl;

3) Then, this command line does it:

fpc -XMSDL_main -k-L/sw/lib -k-lSDL -k-framework -kOpenGL -k-framework -kCocoa -Fu<pathtosdl.pas files> -Fi<pathtosdl.inc files> YourProgram.pas

If you installed the SDL libraries using fink, also add -k-L/sw/lib -k-lSDL to your fpc command.

If sdl.pas and jedi-sdl.inc are in the directory of your program, you can omit -Fu<pathtosdl.pas files> -Fi<pathtosdl.inc files>.


Creating an empty SDL window:

program sdltest;
{$linklib gcc}
{$linklib SDLmain}
uses sdl;
  scr: PSDL_Surface; // Our main screen
  SDL_Init(SDL_INIT_VIDEO); // Initialize the video SDL subsystem
  scr := SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE); // Create a software window of 640x480x8 and assign to scr
  SDL_Quit; // close the subsystems and SDL

You can then compile this code with

fpc -Fu<pathtosdl.pas files> -Fi<pathtosdl.inc files> example.pas

If you use lazarus, make sure you fill the "other unit files" and "include files" properly.


See the Free Pascal meets SDL website for tutorials on using Free Pascal and SDL.