[vorbis] Audio Section - Game Programming Gems 3

[Mercier, Dave]

Re: the standard lib thing - Replacing standard lib functions with your own
implementation isn't as easy as it sounds. For one, I'm a programmer who can
get Vorbis support into a game through another library. I have absolutely no
control over what gets linked into the 30 or 40 games that use that library
though, so "I" can't do anything about that.

Game developers usually do not replace all standard lib functions. The first
rule is they completely avoid their use where possible. Then, they may only
use a handful from the standard library. There may be many functions in a
standard library - let's say the math library has 50 functions in it. The
game may only use 3 or 4 of those. But the way the standard lib code is laid
out, it may link in all 50 in one swoop. Now we certainly don't want to
re-write 50 functions if we may only use 3 or 4 of them. And before you say
it we have no idea which 3 or 4 of the standard lib may be used. Code in a
typical game is contributed by hundreds of programmers, and the projects are
very large, and certainly not everyone knows what everyone else is doing or
needs.

Anyway, if we had a function table of the functions we had to replace, we
could just fill it in with our versions, write custom versions just for the
sake of Vorbis, or we could fill some of them in with standard lib
functions. The Vorbis code should then maybe strive to use as few external
functions as possible to simplify this interface. If something like this
isn't done, it's a case of hack the Vorbis source to make it compatible in
our game, and that's a bad thing if we want to move forward easily (e.g. to
Vorbis V2.0). This is how most of our code works and it makes life easier.
All our audio codecs don't use standard C functions, save maybe memcpy and
memset replacements - of course Vorbis is more complex, and we'll have to do
more work to get it hooked in.

I don't want to push this too hard anyway, I'm just trying to let you know
how it looks from the perspective of one game developer. 

Thanks,
Dave.

-----Original Message-----
From: Michael Smith [mailto:msmith at labyrinth.net.au]
Sent: Friday, November 09, 2001 12:21 AM
To: vorbis at xiph.org
Subject: Re: [vorbis] Audio Section - Game Programming Gems 3

>Ok, this might be completely off-track, and I am probably completely wrong,
>but I have a strange feeling in the back of my head.... Is that memory
usage
>dependent on the size of the stream? Have you tried with very small streams
>(a few seconds) ? How exactly did you measure the memory usage? By checking
>difference before and after opening a decoder, or by calculating it
>manually?

No, he's right - libvorbis memory usage is pretty bad (compared to mp3,
at least). For common cases it can be greatly reduced (with some substantial
work, though), though worst-case will probably still be like this.

>Why don't you create wrapper stubs for stdlib functions? I mean, if you
>don't want to use the stdlib functions and you don't link with them, I
guess
>you must have your implementations, right? So wouldn't it be easy to just
>make wrappers that are named exactly as stdlib functions and that call your
>functions, then liknk with your wrapper library instead of the stdlib?
>It is same effect as doing vectorization, it requires approximately the
same
>effort on your side, yet it doesn't require a single line of code changed
in
>vorbis.
>What do you think?

Yes. This is a much, much better way of doing things.

Michael

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