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).
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 );
Addr1 := cardinal( Pixels );" gets "Addr1 := PtrUInt( Pixels );
line := PUint8(Integer(line) + flic.Surface.pitch);" gets "line := PUint8(PtrInt(line) + flic.Surface.pitch);
Definition of PTRUINT and PTRINT for non-FPC compilers:
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.