Re: [Plib-devel] Exposed bitmap loaders in SSG?

[steve <sjb...@ai...>]

Jan Reucker wrote:
> Hello!
> 
> In August 2005 I wrote to this list asking what you'd think about
> exposing the bitmap loader functions from SSG. This would allow
> PLIB users to use these loaders for more than only texture loading,
> or it would simplify writing more complex texture classes for
> SSG. During the last 1.5 years I didn't find the time to start the
> project for which I needed this, but now it would really come in 
> handy.

Yeah - I've been thinking for a long time that we could use a proper
set of image loaders somewhere in PLIB...and if we had them it would
make sense to change the SSG texture map loaders to use them.

But if we are going to do this - let's think carefully up-front and
do it properly.

If you want to take on this task, I think you should start a new
PLIB library component (plibImage with a 'pi' prefix or something)
- get it all up and working as a stand-alone thing (probably
copying/stealing code from SSG to do that).   When it's all running
and reliable, we could just switch SSG over to using it.  This would
mean zero changes to SSG until we are ready to do the switch.

One thing though - we need to be careful about adding external
dependencies.  Relative lack of external dependancies is one of
the things people really value about PLIB and we don't want to
lose that.

I'd like to avoid having PLIB require libjpeg, libpng and a bunch of
other libXXX's before it'll compile.  Whilst you can rely on those
being present in Linux these days, they aren't always there under
Windows and MacOSX.

On the other hand, we don't want to copy the code from those
libraries into PLIB (thereby causing a code-fork for those
projects) and we CERTAINLY don't want to be writing and maintaining
our own JPEG and PNG loaders!

I think we should consider dynamically loading those libraries
(using dlopen/dlsym/dlclose) on-demand so that PLIB will still
build and run without any external image libraries if the user
only wants to use '.rgb' images.

The system should have a 'piInit()' call that goes out and looks
for available libXXX's (where 'XXX' is png, jpeg, gif, tif, etc)
and posts a list of available loaders that one can easily query
from the application level.  eg

    piInit() ;

    if ( piHaveLoaderFor ( "png" ) )
      image = piImageFactory ( "myimage.png" ) ;
    else
    if ( piHaveLoaderFor ( "jpg" ) )  // Urgh - lower quality!
      image = piImageFactory ( "myimage.jpg" ) ;
    else
      ulSetError ( UL_FATAL, "Can't load myimage because both"
                             " libpng and libjpeg are missing" ) ;