Re: R: [Plib-users] Transparent texture

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

Paolo Leoncini" <p.l...@ci...> wrote:

> The easy explanation could be that all works ok, and I'm doing something
> wrong...

That's what I'm going with right now!

> but the fact is that I don't set anything special for getting
> trasparent textures, other than to supply the alpha-equipped [2/4
> compoments] texture.
> The little step forward, that anyway doesn't solve the general problem, is
> to set
> 
> materials[...]->setAlphaClamp(0.5f)
>
> into the 3DS loader. This actually rises the threshold of the transparent
> part with respect to the opaque, but I'm still in trouble with the full
> [0:255] alpha range support in rgba/inta textures.

I don't know offhand what the 3DS loader is doing with that field...however,
transparency *certainly* works in SSG - I use it constantly in all sorts
of applications.

Here is the code I use to set up an ssgSimpleState in my latest project:

  /* Declare it... */

  *gst = new ssgSimpleState ;

  /*
    I allocate a simple integer index to every State
    to make it easier for my collision detection code
    to tell me what kind of material we collided with.
  */
 
  (*gst) -> setExternalPropertyIndex ( index ) ;
 
  /*
    Load up the texture...or not.
  */

  if ( texture_map [ 0 ] != '\0' )
  {
    (*gst) -> setTexture ( texture_map, !(clamp_tex & UCLAMP),
                                        !(clamp_tex & VCLAMP) ) ;
    (*gst) -> enable ( GL_TEXTURE_2D ) ;
  }
  else
    (*gst) -> disable ( GL_TEXTURE_2D ) ;

  /*
    Turn on lighting...or not
  */
 
  if ( lighting )
    (*gst) -> enable ( GL_LIGHTING ) ;
  else
    (*gst) -> disable ( GL_LIGHTING ) ;

  /*
    Set up some other things I use a lot
  */
 
  (*gst) -> setShadeModel ( GL_SMOOTH ) ;
  (*gst) -> enable ( GL_COLOR_MATERIAL ) ;
  (*gst) -> enable ( GL_CULL_FACE      ) ;
  (*gst) -> setColourMaterial ( GL_AMBIENT_AND_DIFFUSE ) ;
  (*gst) -> setMaterial ( GL_EMISSION, 0, 0, 0, 1 ) ;
  (*gst) -> setMaterial ( GL_SPECULAR, 0, 0, 0, 1 ) ;
  (*gst) -> setShininess ( 0 ) ;

  /*
    Set up transparency...or not
  */
 
  if ( transparency )
  {
    (*gst) -> setTranslucent () ;
    (*gst) -> enable ( GL_ALPHA_TEST ) ;
    (*gst) -> setAlphaClamp ( alpha_ref ) ;  /* 0..1 */
    (*gst) -> enable ( GL_BLEND ) ;
  }
  else
  {
    (*gst) -> setOpaque () ;
    (*gst) -> disable ( GL_BLEND ) ;
  }                                                                             

I have noticed that my GeForce-256 card (running the nVidia OpenGL-for-Linux
driver) seems to misbehave a little with some values of AlphaClamp.

> Does anybody work with full alpha'ed textures for special effects in
> plib/ssg-based games?

Yes.

> I read 3DS files for tests, so if anyone does it with
> (secene data) in a different format, it could lead to understand that there
> is some bad setting in the 3DS reader, so we could modify it...

Well, I find that modellers in general do a very poor job of giving me the
exact 'material' parameters that I need - so my applications generally
load a table of material properties that I create by hand (either as a
parsed ASCII file - or hard-coded into the application).  As the model
is loaded, I match up the texture map that was applied to the model to
the texture map name in my application's material property table.

The 'ssgSetAppStateCallback(getAppState)' callback does this.

Hence, I don't care what the loader does with material properties...so
there could easily be a bug.

> Sorry for insisting on it, but I'm very disappointed (still loving plib,
> anyway!) -

Well, don't worry too much - it *does* work in the core of SSG - so either
you are not setting it up right or the 3DS loader is broken.

From your description, it seems like you probably don't have...

    ssgstate -> enable ( GL_BLEND ) ;

...set.  If you don't have that then OpenGL will still compute
alpha values - but it won't BLEND the new polygon into the
background - it'll either be on or off - opaque or *nothing*.

So, check that out - and if you are still getting nowhere,
*someone* will need to take a look into the ssgState stuff
in the 3DS loader.


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