Tag Archives: faq

Which SDL2 unit to choose?

Last updated on August 13th, 2022

Right now I’m aware of these translation projects that provide SDL2 units (if you know a further one, let me know):

SDL2 for Pascal units Pure translation of SDL2 source files. It is based on a fork of Tim Blume's SDL2 units, but is updated quite regularly.
Tim Blume's SDL 2.0 units Pure translation of SDL 2.0 source files. The original, modular structure of the header files is preserved, so the SDL2.pas is composed of many include files. Translations of SDL2_mixer, SDL2_ttf and SDL2_image are available, SDL_net seems to be missing so far. It provides MacOS X support.
Daniel Plachotich's SDL 2.0 units Pure translation of the SDL 2.0 source files. All the header files of the original SDL 2.0 source code are combined into one large SDL2.pas (similar to JEDI-SDL's SDL.pas for SDL). Translations of SDL2_mixer, SDL2_ttf, SDL2_image and SDL2_net are available. The MacOS X support is unproven.
LazSDL2 units Heavily modified SDL 2.0 units to allow for dynamic loading of the library by Imants Gulis.
Bare Game Library Bare Game is a game library which is put on top of the SDL2 library. It also allows for easy combination of SDL2 with Lazarus, which is a great plus. [Official website (baregame.org) is down, is the project dead?]

Now we go for a detailed discussion of them.

Modified header translations

Well, the Bare Game Library is a great project and I like the idea to provide an easy-to-use game development library  very much but it isn’t suitable to learn pure SDL 2.0. Many functions are wrapped by new function names, you would learn much about the usage of Bare Game, fewer about SDL 2.0 itself. Also, the ease of use is traded for flexibility, e.g. there is just support for Windows and Linux, no Mac support, and you are more or less forced to use Lazarus IDE (which is an excellent choice, no question!) but for some reason you might not want to use Lazarus. The usage of libraries always trades ease for flexibility. And finally you are dependent upon a second project. If SDL 2.0 is updated, will Bare Game have updates, too? Bare Game is a great project at all, but for learning SDL 2.0 and if you keep the downsides in mind, it is not the best choice here. It has been updated back in 2019 the last time.

Imants Gulis’ LazSDL units allow for dynamic loading of SDL 2.0, hence your application decides during run-time if SDL 2.0 has to be loaded. This led to heavily modified unit files compared to the original header files. Also it is expected to use Lazarus. Although there are numerous cases where dynamic loading can be a great plus, for the tutorial and a wide variety of applications this is not necessary. The last update is from 2016.

Pure header translations

The unmodified header translations of the original SDL 2.0 headers is the best choice when it comes to learning SDL 2.0.

The beauty of Daniel Plachotich’s SDL 2.0 units is the fact that there are exactly five files you need. They contain all the translations for basic SDL 2.0 and the official extensions SDL2_mixer, SDL2_ttf, SDL2_image and SDL_net. Unfortunately, the original comments are cut out. This is a major drawback to my mind. Sometimes you need just a quick look at the implementation of a function in the source to get how it works or what is wrong. Also the MaxOS support is unproven. The last update happened in 2015.

In contrast Tim Blume’s SDL 2.0 units kept the comments. The unit names differ slightly from the original names (e.g. SDL_audio.h got sdlaudio.inc instead of SDL_audio.inc ), which I don’t like, but it is acceptable. This allows for a better understanding in how SDL 2.0 works. Also it allows for better flexibility with regards to later projects.

After a lack of updates for one year, the PGD Community decided to fork Tim Blume’s units and establish SDL2 for Pascal. It is a regularly updated version of Tim Blume’s units and has changed drastically as a result.


This said, to my mind, the best choice to start with SDL 2.0 and Free Pascal: Go for the units of SDL2 for Pascal. For other purposes, other units may be the better choice.

Does SDL provide 64 bit compatibility?

Yes, SDL is 64 bit compatible.

If you experience troubles: First of all, make sure the problem is really caused by the 64 bit operating system you use. Does the program run without any problems if run it in a 32 bit operating system?

Make sure, that the Free Pascal compiler you use is the 64 bit version. There are different links on the download page of Free Pascal to different 64 bit operating systems for different architectures (Intel, AMD, PowerPC), so did you install the right 64 bit version of FPC?

If all this applies and you still get an error saying

sdlutils.pas Warning: Conversion between ordinals and pointers is not portable


sdlutils.pas Error: Typecast has different size (4 -> 8) in assignment

(or similar messages) then your problem clearly is related to 64 bit compatibility.

In the FPC reference is written about this type-checking error:

If you typecast a pointer to an ordinal type of a different size (or vice-versa), this can cause problems. This is a warning to help in finding the 32-bit specific code where cardinal/longint is used to typecast pointers to ordinals. A solution is to use the ptrint/ptruint types instead.

That is exactly what is done by sdlutils.pas and many other files and causes the errors and warnings!

In other words, the size of pointers and integers is different on 64 bit systems. They should be of same size to make conversion safe. To circumvent this problem you have to replace a conversion of UINT32(POINTER) by PTRUINT(POINTER) and INTEGER(POINTER) by PTRINT(POINTER). The PTRUINT and PTRINT integer types are always the same size as the pointer by definition. For FPC users both types are introduced since version 1.9.3. For other compilers (e.g. Delphi, Kylix, GPC, …) they are not and you have to define them yourself (see below).


1) sdlutils.pas:

p := Pointer( Uint32( SrcSurface.pixels ) + UInt32( y ) * SrcSurface.pitch + UInt32( x ) * bpp );" gets "p := Pointer( PtrUInt( SrcSurface.pixels ) + UInt32( y ) * SrcSurface.pitch + UInt32( x ) * bpp );

2) sdlutils.pas:

Addr1 := cardinal( Pixels );" gets "Addr1 := PtrUInt( Pixels );

3) sdl_flic.pas:

line := PUint8(Integer(line) + flic.Surface.pitch);" gets "line := PUint8(PtrInt(line) + flic.Surface.pitch);

Definition of PTRUINT and PTRINT for non-FPC compilers:

{$ifndef FPC}


PtrInt = LongInt;

PtrUInt = LongWord;


There is a patch which is replacing all the questionable parts of the JEDI-SDL package, so you wouldn’t have to do it manually. Furthermore it is introducing the definition of the new types for non-FPC compilers. Link: Patch for 64 bit support. Unfortunately it is only useful if you manage your JEDI-SDL files by CVS or SVN. Nevertheless you could download the patch and check what the patch is changing and how to do it properly (the examples are generated from the patch).

More infos about this topic in the forum: Forum discussion about 64 bit compatibility. Thanks to Cybermonkey for his helpful response.

What is SDL and SDL2?

SDL is the abbreviation of Simple DirectMedia Layer.

Originally when refering to SDL, SDL 1.2 was meant. It is the predecessor of modern SDL 2.0 (sometimes SDL2). Nowadays, when refering to SDL, it depends on context if you really mean the old SDL 1.2 or the modern SDL 2.0.

The  obsolete SDL 1.2 and the modern SDL 2.0 are a set of units which provide a free, easy and platform-independent access to features needed for developing high performance games and applications. This includes easy access to graphic, sound and input handling (keyboard, mouse, joystick) for Free Pascal and other Pascal dialects.

Who made SDL and SDL2?

SDL was developed between 1998 and 2001 by Sam Lantinga, the chief programmer of the software company Loki Games. In 2002 the company got bankrupt, but Lantinga went on developing SDL. So it got updated continuously  until today.

In August 2013 the successor SDL 2.0 has been released. SDL 2.0 introduces a lot of new features which allow development of high performance applications using up-to-date technologies.

Although the original library isn’t written in Pascal, fortunately the SDL 2.0 headers got translated to Pascal by Tim Blume and others, so the SDL 2.0 library is usable for Pascal developers as well.

What is this page about?

This page is made to help you to start with the SDL and/or SDL2 (Simple Directmedia Layer) library under Free Pascal (or other Pascal dialects) and to acquaint yourself with SDL’s concepts and commands.

Be aware though that my tutorials gives just a brief overview and introduction to the SDL and SDL2 library and are far from being all-embracing.

The tutorials aim at Pascal programmers knowing the basic concepts (loops, functions, pointers) of Pascal and now like to progress to SDL and/or SDL2.