Re:Re: Changing Material again

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Marco Crocetta (onyx++at++datamat.it)
Wed, 15 Mar 95 10:07:45 MET

On Mar 14, 9:57am, John Rohlf wrote:
> Subject: Re: Changing Material again
> >
> > > Now pfMtlColorMode with the mode PFMTL_CMODE_COLOR
> > > seems to have the effect of disabling the primitive colour...
> > > Where is my mistake?
> >
> > I've had the same problem in the past. The issue is that PFMTL_CMODE_COLOR
uses
> > the material parameters in lmbind and disables the modification of material
> > properties with calls like cpack & c4f. See the manual entry of the Iris GL
> > call lmcolor(). The performer colour per primitive code relies on this sort
of
> > colour shortcut.
> >
> > I found this frustating too. The GL manual says it's possible to specify
> > material alpha with lmcolor(LMC_AD) but the performer manual says it only
> > supports alpha on unlit geometry or lmcolor(LMC_COLOUR) lighting, this
_may_
> > not be as black and white as it seems.
>
> Tell me where the performer documentation says this so we
> can fix it. Performer's use of lmcolor/glColorMaterial is identical
> to GL's so alpha specified at the geoset level will have effect
> if the material's colormode is PFMTL_CMODE_AD or PFMTL_CMODE_DIFFUSE.
>
>
>
>-- End of excerpt from John Rohlf

Hi,

page 198 of IRIS Performer Reference Pages says:

1)"pfMtlAlpha specifies the alpha om mtl in the range 0.0 through 1.0. If
   trasparency is enabled (see pfTransparency), a material whose alpha is < 1.0
   and whose color mode is PFMTL_CMODE_COLOR will be transparent with alpha of
     1.0 being completely opaque and 0.0 being completely transparent. The
default
   alpha value is 1.0, or completely opaque. "

But this mode disable the original primitive color (not only the 4th
component).
Later in the same page about pfMtlColorMode:

2) "...Specifically, this settings allows color specified by pfGeoSets to have
     effect. When lighting is disabled, the colorproperty of the current
material. Alpha, the fourth color mode is set to PFMTL_CMODE_COLOR."

And finally in my (old) GL Programming guide a read
(page 9-20; 9.6.5 Transparency):

3) " The use of LMC_DIFFUSE or LMC_AD mode overrides the ALPHA material
property
    with the alpha of the current color."

And this is in agreenment with point 1.
And finally I read on the man pages lmcolor(3G) this last thing that
seems to be in contrast with point 3.

4) "LMC_AD, .... Alpha, the fourth color component specified by RGB color
           commands will set the ALPHA property of the current material."

I hope this will help you to fix the problem (if any).
Please let me know your point of view about changing only the material
alpha.

Thanks in advance

-- 
----------------------------
MARCO CROCETTA
DATAMAT SpA, Rome
e-mail: onyx++at++datamat.it
----------------------------

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