plib-users

[Plib-users] Transparent texture

[Paolo L. <p.l...@ci...>]

Why in SSG my transparent (rgba/inta) textures appear with a sharp
transition from alpha=255 to alpha<255, like 1-bit alpha?

Better explained, whilst alpha channel is fully exploited (i.e. [0:255]
range), transparent area on such textures is limited to where alpha is 255.
This obviously results in a bad "halo" where, let's say, 0<alpha<255, and
effects like steam, smoke are thus impossible to be done thru textures.

Should I enable some special flag in the state node? (the image loader
correctly understand the zsize 2 or 4 of such textures).

Greetings -

Paolo

----------------------------------------------------------------------------
-
Paolo Leoncini						phone:  +39 (0823) 623134
Scientific Visualization Group			fax:    +39 (0823) 623126
CIRA - Italian Center for Aerospace Researches	p.l...@ci...
Via Maiorise - 81043 Capua (CE) Italy		www.cira.it/research/vis

R: [Plib-users] Transparent texture

[Paolo L. <p.l...@ci...>]

Dear plib/ssg friends,

I didn't hear anything related to the subject, and I am a bit surprised that
a community around a game-oriented library is not much sensitive to it.
The easy explanation could be that all works ok, and I'm doing something
wrong... 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.

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

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

Paolo

----------------------------------------------------------------------------
-
Paolo Leoncini						phone:  +39 (0823) 623134
Scientific Visualization Group			fax:    +39 (0823) 623126
CIRA - Italian Center for Aerospace Researches	p.l...@ci...
Via Maiorise - 81043 Capua (CE) Italy		www.cira.it/research/vis

> -----Messaggio originale-----
> Da: pli...@li...
> [mailto:pli...@li...]Per conto di Paolo
> Leoncini
> Inviato: martedì 6 giugno 2000 12.06
> A: pli...@li...
> Oggetto: [Plib-users] Transparent texture
>
>
> Why in SSG my transparent (rgba/inta) textures appear with a sharp
> transition from alpha=255 to alpha<255, like 1-bit alpha?
>
> Better explained, whilst alpha channel is fully exploited (i.e. [0:255]
> range), transparent area on such textures is limited to where
> alpha is 255.
> This obviously results in a bad "halo" where, let's say, 0<alpha<255, and
> effects like steam, smoke are thus impossible to be done thru textures.
>
> Should I enable some special flag in the state node? (the image loader
> correctly understand the zsize 2 or 4 of such textures).
>
> Greetings -
>
> Paolo
>
> ------------------------------------------------------------------
> ----------
> -
> Paolo Leoncini
> phone:  +39 (0823) 623134
> Scientific Visualization Group			fax:    +39
> (0823) 623126
> CIRA - Italian Center for Aerospace Researches	p.l...@ci...
> Via Maiorise - 81043 Capua (CE) Italy		www.cira.it/research/vis
>
>
> _______________________________________________
> plib-users mailing list
> pli...@li...
> http://lists.sourceforge.net/mailman/listinfo/plib-users
>

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)

R: R: [Plib-users] Transparent texture

[Paolo L. <p.l...@ci...>]

Thanks, Steve, for the useful suggestions - I finally saw those
semi-translucent textures in my database. What I did? these simple three
things:

1. glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA )
   so to not actually need alpha planes still getting roughly good blending;

2. mat->enable( GL_BLEND ) and mat->setAplhaClamp(0.01)
   the latter to get the full [0:255] alpha range;

3. switch for tests to a AccellGraphics GMX2000-equipped NT box (!!!!)
instead of my G200 on NT, which soon switch to software with as few as
2.5Mtexels loaded and doesn't want to know about alpha-ed textures (latest
driver, of course).

Since I would like to rely on (3DS) modeller's information as much as
possible, a further little work will focus on automatically set those
properties for transparent textures (only the image loader knows about the
2/4-components) - the AppStateCallback seems once again the final resource.
Furthermore one has also to "isolate" translucent objects from the rest of
the database for rendering with z-buffer disabled after all other objects,
for best blending results.

Thanks again -

----------------------------------------------------------------------------
-
Paolo Leoncini						phone:  +39 (0823) 623134
Scientific Visualization Group			fax:    +39 (0823) 623126
CIRA - Italian Center for Aerospace Researches	p.l...@ci...
Via Maiorise - 81043 Capua (CE) Italy		www.cira.it/research/vis

> -----Messaggio originale-----
> Da: pli...@li...
> [mailto:pli...@li...]Per conto di Steve Baker
> Inviato: venerdì 16 giugno 2000 21.02
> A: pli...@li...
> Oggetto: Re: R: [Plib-users] Transparent texture
>
>
> 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)
>
> _______________________________________________
> plib-users mailing list
> pli...@li...
> http://lists.sourceforge.net/mailman/listinfo/plib-users
>

Re: R: R: [Plib-users] Transparent texture

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

Paolo Leoncini wrote:
> 
> Thanks, Steve, for the useful suggestions - I finally saw those
> semi-translucent textures in my database. What I did? these simple three
> things:
> 
> 1. glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA )
>    so to not actually need alpha planes still getting roughly good blending;

Yep - only a few rather esoteric algorithms actually need destination
alpha - and quite a few graphics cards don't support them.

> 2. mat->enable( GL_BLEND ) and mat->setAplhaClamp(0.01)
>    the latter to get the full [0:255] alpha range;

Yep.
 
> 3. switch for tests to a AccellGraphics GMX2000-equipped NT box (!!!!)
> instead of my G200 on NT, which soon switch to software with as few as
> 2.5Mtexels loaded and doesn't want to know about alpha-ed textures (latest
> driver, of course).

I'm not familiar with Windoze drivers - but a board shouldn't switch
to software rendering just because you are using too much texture memory.
It might take a while to swap maps in and out of memory - but it's probably
still hardware accellerated.

Dunno why G200 would have trouble with alpha - it works OK under Linux.

> Since I would like to rely on (3DS) modeller's information as much as
> possible, a further little work will focus on automatically set those
> properties for transparent textures (only the image loader knows about the
> 2/4-components) - the AppStateCallback seems once again the final resource.

Well, I guess whatever the problem is should be fixed - but I still believe
that most applications will want to use AppStateCallback in the end.

> Furthermore one has also to "isolate" translucent objects from the rest of
> the database for rendering with z-buffer disabled after all other objects,
> for best blending results.

SSG does that automatically for you.

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