add optional libXfont2 support

[stefan11111]

Same PR as #13 ,but everything squashed in one single commit.

[stefan11111]

@clbr @rofl0r
Any other concerns I should address?

[rofl0r]

using the header, the diff is much cleaner now, except that you suddenly changed the fpe type so now we have . vs -> accessing the field, which makes it a bit of a mess again.

[stefan11111]

using the header, the diff is much cleaner now, except that you suddenly changed the fpe type so now we have . vs -> accessing the field, which makes it a bit of a mess again.

@rofl0r The reason I did that is because of how libXfont2 handles the fpe functions.

I based this libXfont2 port on Xorg code, specifically this patch: https://lists.freedesktop.org/archives/xorg-devel/2016-May/049769.html

I tried to see if I can somehow make fpe_functions a regular pointer instead of an indirect pointer, but I couldn't. If you see some way to do that that I missed, let me know an I'll try to update my patch.

I changed all the accesses to indirect accesses so that I don't have ifdef's for libXfont1 direct accesses vs libXfont2 indirect accesses.

I am pretty sure the compiler optimizes out the indirect accesses in the libXfont1 case, but I could use
'_X_EXPORT FPEFunctions ** const fpe_functions = &_fpe_functions;' to help it a bit.
In any case, the overhead is very small for direct vs pointer access, way smaller that the actual call.

[stefan11111]

@Rofl0l Fixed the 2 things you pointed out and added the const I mentioned in my above comment.

I can get rid of one more ifdef in dix/main.c with something like '#define ResetFontPrivateIndex(...)', an empty function define to remove a call that doesn't happen with libXfont2. Should I do that too?

[rofl0r]

i'm just providing some advice on how i would do things to make them less awful :)
though i have no idea what the maintainers think about the whole thing, and they're the people that have to say yay or nay. if i was the maintainer, i'd be inclined to merge it if the ugliness can be kept to a minimum.

[stefan11111]

@rofl0r I added the empty function define too.
My concern with using the preprocessor is to not obfuscate things. That's why I ask what approach I should take with this. Should it be desired, I can add something like '#define FOO_C_INSIDE' for every file I put an ifdef in, and that would allow me to move everything about the libXfont version switch to the header. I think going that far would be too much obfuscation, but I can do that if it's desired.

Btw, are you not a tinyx or tinycorelinux dev? I assumed you were since I saw you comment in various issues and PR's.

[rofl0r]

nope, @sabotage-linux dev here.

[stefan11111]

@clbr
ping

[clbr]

Sorry, can't review right now.