I can't switch to an opaque texture. For example, a texture of a tree
*MUST* have an alpha component. I've faded-out polygons over time
before... no big deal. Just adjust the TransparencyAttributes of the
Appearance.
By the way, I am *modulating* the texture with the object. This allows
for *LIT* textures.
In the OpenGL Redbook, there is a table showing how the color(C) and
alpha(A) of the final pixel is computed based on the texture color (Ct),
texture alpha(At), poly color(Cp), and poly alpha (Ap), for each of the
image formats and texture functions.
For GL_RGBA (which is what I'm using for my transparent textures):
Function=Replace Function=Modulate
C = Ct C = Cp * Ct
A = At A = Ap * At
Function=Decal
C = Cp(1-At) + Ct * At
A = Ap
Accoding to this, for *modulate*, the alpha (transparency) of my polygon
should be MULTIPLIED by the alpha of the texture. Thus, a totally
transparent polygon should be just transparent, including the texture.
The places where the texture alpha is 0, the polygon SHOULD NOT BE
VISIBLE. Yet, this is not the case. Perhaps this is a bug?? I think
it is time for a test app to show others (Sun)...
-Lee
J. Lee Dixon
Software Engineer
SAIC - Celebration, FL
[EMAIL PROTECTED]
-----Original Message-----
From: Yazel, David J. [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, September 19, 2000 11:26 AM
To: [EMAIL PROTECTED]
Subject: Re: [JAVA3D] Fade-out of transparency textured polygons
Ah! hehe, I thought you meant over distance. I have not "faded out" a
polygon over time. This is what I would try: do not make the polygon
transparent, instead modulate a completely opaque texture on your
polygon.
Since we are modulating, changes to the colors of the polygon should
mixed
with the texture....I'm guessing you could change the materials and
adjust
their alpha componant? Or adjust the vertex colors (with the geometry
update callback) to smoothly update thier vertex alphas? Or possibly
use a
referenced texture (and on a transparent polygon) and update the alphas
across your texture (using a graphics handle you can draw() on).
Can't think of anything else to try. The easiest thing would be to just
adjust the polygon transparency attributes, but like you said, that
doesn't
work when you have a alpha blended texure.... this is probably because
adjusting the transparency attributes of a polygon is probably just
adjusting the vertex alphas, and since you are blending and not
modulating
you don't get the effect.
Dave
> ----------
> From: J. Lee Dixon[SMTP:[EMAIL PROTECTED]]
> Reply To: Discussion list for Java 3D API
> Sent: Tuesday, September 19, 2000 10:58 AM
> To: [EMAIL PROTECTED]
> Subject: Re: [JAVA3D] Fade-out of transparency textured polygons
>
> I mentioned that my polygon was already fully transparent to support
the
> alpha channel texture. The alpha component of the polygon does not
seem
> to affect the transparency of the texture when the texture has an
alpha
> channel.
>
> I guess I could also be more specific. When I say "fade-out", I mean
> fade over *time*, not over distance.
>
> -Lee
>
> -----Original Message-----
> From: Yazel, David J. [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, September 19, 2000 10:16 AM
> To: [EMAIL PROTECTED]
> Subject: Re: [JAVA3D] Fade-out of transparency textured polygons
>
>
> Hmmm,
>
> Two ways:
>
> 1) Interesting way but probably not what you want is to set the color
of
> the
> vertex to include an alpha component and fade across your vertices,
> using
> modulate with the texture. I know this works in opengl, I assume it
> does in
> Java3d.
>
> 2) The next way is to use a transparent polygon, and blend a texture
in
> which has an ever increasing (decreasing?) alpha, this is the
technique
> I
> use to make a terrain transition, I overlay two meshes and fade one
out.
>
> Dave
>
> > ----------
> > From: J. Lee Dixon[SMTP:[EMAIL PROTECTED]]
> > Reply To: Discussion list for Java 3D API
> > Sent: Tuesday, September 19, 2000 8:42 AM
> > To: [EMAIL PROTECTED]
> > Subject: [JAVA3D] Fade-out of transparency textured polygons
> >
> > A while back I fought with the settings to make transparency
textures
> > work. I could easily place the texture on the polygon, but the
places
> > where the alpha value of the texture was 0, it showed the color of
the
> > polygon. It didn't make sense to me that I could see the underlying
> > polygon at all.
> >
> > I fixed the problem by setting the TransparencyAttributes to be
> totally
> > transparent. Fine.
> >
> > Now, how do I make the whole object fade out?? Normally, I would
fade
> > using the TransparencyAttributes, but it is already set to totally
> > transparent.
> >
> > I thought applying a texture with alpha set to 0 would make the
> polygon
> > invisible; I shouldn't have to set the poly transparency as well...
> >
> > -Lee
> >
> > J. Lee Dixon
> > Software Engineer
> > SAIC - Celebration, FL
> > [EMAIL PROTECTED]
> >
> >
>
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