Re: [Alephmodular-devel] Platform-independence structure (was: Developer Rant #1 :) )

[Woody Z. I. <woo...@sb...>]

On Tuesday, January 14, 2003, at 10:21  PM, Timothy Collett wrote:

> Just to step into this debate a minute...
>
> I don't know all that much about SDL.  If we made AM be largely 
> SDL-dependent, would that mean that one would have to install SDL to 
> run AM?  That is, could all the relevant libraries (reasonably) be part 
> of AM itself, or do they have to be installed separately?

Others have talked about the situation on Mac OS X (can be bundled with 
the application).  FWIW, Windows lets you put the .dll's in the file 
with the executable, which is how A1/SDL for Windows currently works.  
(No need to install SDL separately or place things in your system 
directories etc.)

> Also, what are the different important parts of SDL, how exactly could 
> each be used within AM, and how much interdependence is there among 
> them?

This is too big a question to really answer, but briefly, the purpose of 
SDL is to provide a common interface across a very wide variety of 
platforms for the following:

*	Video (i.e. gaining byte-level access to the framebuffer, blitting 
2D surfaces, getting an OpenGL context, setting the screen mode and bit 
depth, etc.)
*	Window Manager (very little in here, mostly resize window and 
toggle fullscreen)
*	Event Handling (processing mouse clicks, keystrokes, etc.)
*	Joystick
*	Audio (very low-level access, you provide the bytes for the sound 
card to play back)
*	CDROM (using CD-ROM drive as CD audio player)
*	Threads
*	Timers (getting time values, waiting, and asking for periodic 
scheduling)
*	Endian-independence (byte-swapping)
*	Main (providing a single source-code entry point for you so you 
don't have to worry about things like WinMain() on Windows)

Those are in the core "SDL".  Each is essentially an independent 
subsystem which can be used with or without the rest.

SDL_net contains, essentially, nonblocking TCP and UDP sockets, select() 
(i.e. wait for data arrival etc.), and DNS name-to-host resolution.  
(Many platforms have BSD sockets or something a lot like them, so this 
isn't too exciting in most cases, but it does serve to hide the little 
differences.  Also, significantly, it works in Mac OS 9, which does 
*not* have a sockets-like programming API on its own.)  SDL_net requires 
SDL, but only (as noted) for SDL_GetError() and SDL_SetError().  I 
suppose you could probably provide your own implementations for those 
symbols if you really wanted to dump SDL and only use SDL_net.

SDL_image lets your code load the following image formats into an SDL 
surface, suitable for byte-level inspection/manipulation (e.g. setting 
up in an OpenGL texture) or blitting with the SDL Video subsystem: BMP, 
PNM, XPM, LBM, PCX, GIF, JPEG, PNG, TGA.  I suppose it requires the SDL 
Video subsystem.

(From the SDL_mixer site:) SDL_mixer is a sample multi-channel audio 
mixer library.  It supports any number of simultaneously playing 
channels of 16 bit stereo audio, plus a single [stereo] channel of 
music, mixed by the popular MikMod MOD, Timidity MIDI, Ogg Vorbis, and 
SMPEG MP3 libraries.  (end quote)  It does require the free SMPEG and 
libvorbis libraries for MP3 and Ogg Vorbis support.  (MikMod, which can 
play virtually any file in the (large) MOD family, is built in directly.)

See www.libsdl.org for more information.

> The reason I ask these things is that I am leaning, along with Br'fin, 
> strongly in the direction of having SDL be a separate platform.  My 
> main reasons are two: dislike of dependence on separately-installed 
> libraries and dislike of SDL widgets.

Well I think we've talked about the first one pretty well (though I 
don't know how it works in Linux etc., IIRC in Mac OS 9 you can also put 
the library in the folder with the application and have it work - oh 
right, Mac OS 9 supports bundles too, so the user wouldn't even have to 
see it).

Anyway I assume the plan is probably to use SDL_net anyway...?  which 
means some of the libraries will be there regardless.

I'm not sure what you guys are talking about with this SDL widget 
business.  Though there are several cross-platform, typically 
game-oriented GUI libraries out there that are built on top of SDL, SDL 
itself has no "widgets".  The stuff used in A1 was written by Christian 
Bauer for A1 and tweaked up a bit by me.

Woody