Re: [Plib-devel] User defined texture formats

[Steve B. <sjb...@ai...>]

Trent Gamblin wrote:
> 
> * Steve Baker <sjb...@ai...> wrote:
> > OK - but I don't think this is the place to load textures.
> >
> > Shouldn't this just be the (existing) ssgGetAppState callback?
> 
> I'm really confused. Is there any code or examples that use
> ssgGetAppState to load a different image format? An example would be
> really helpful.

Well, my TUx game (http://tuxaqfh.sourceforge.net) uses the ssgGetAppState
callback - but not to load different image formats.  Check out 'material.cxx'.

However, it goes like this:

  * You set up a function as the callback.

  * Whenever the loader needs to create an ssgState, it
    calls your function with the name of the texture.

  * In your function, you allocate (or choose a pre-allocated)
    ssgState and populate it (which could include loading the
    texture for it).

  * If you return a valid ssgState, the loader will use it for
    that leaf.

  * If you return NULL, the loader will create one for you.

The deal is (IMHO) that loading textures whenever an input
file tells you to is pretty inefficient.  Most games are
likely to load MANY models - and this can easily result
in multiple copies of the texture being loaded - which is
VERY wasteful.

Also, there is frequently a need to attach user data to
an ssgState because your game needs to know other things
about the polygon than just the more obvious visual
properties.

My Tux game stores the coefficient of friction for example,
so that our Penguin Pal can slide down icy slopes.  Since
the needed information isn't in the model file anywhere,
it's necessary for the game code to somehow maintain a
table of what properties belong to what materials.

I pre-load all the textures I think I'm going to need,
create a bunch of ssgSimpleState objects - one for each
pre-designed material.

Then when a model is loaded, if the texture map in the file
agrees with the name of the map on one of my pre-defined
materials, it gets that - otherwise I let the loader
set it up.

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjb...@ai... (home)  http://www.woodsoup.org/~sbaker
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