[Radiance-general] Re: Help with transfunc

Mon, 2 Feb 2004 09:07:33 -0500 (EST)

Obviously, *I* should have given this more thought. What I
wanted wasn't represented by the formula that I originally
wrote. I mistook the Rdot for 1/Rdot, and I didn't realize
that I needed to flip the normal if I was looking at the
back of the object.

Anyways, I present, then, a Radiance method for rendering
an x-ray of an object:

------
# include some background light source
void light bc
0 0 3  1 1 1
bc source back
0 0 4  0 1 0  180

# then, the surface modifiers for every "x-rayed" object
void brightfunc trans_mod
2 0.6+0.35*abs(Rdot) .
0
0

trans_mod trans mc
0
0
7 1 1 1 0 0 1 1
------

And the results:
http://mark.technolope.org/image/p51_droplet_no_6/img02_750.jpg

Mark

On Sat, 31 Jan 2004 [email protected] wrote:

> Obviously, I should have given this a little more thought.  I just
> copied the function you had straight into the formula, without
> doing anything to keep it in a legal range.  The following is better,
> but since I don't know what you're trying to do with this formula,
> you should probably think about fixing the range or the formula
> yourself.
>
> void brightfunc trans_mod
> 2 bound(0,1-.6667/Rdot,1) .
> 0
> 0
>
> trans_mod trans surf_dens
> 0
> 0
> 7 1 1 1 0 0 1 1
>
> Sorry.
> -Greg
>
> Quoting Mark Stock <[email protected]>:
>
> > I tried what you suggest (and some minor variations of that with
> > rview from a 3.6a release in December. The window popped up and
> > I saw a handful of multicolored pixels (there's no color at all
> > in my scene), and then SegFaulted. I'm going to try it with the
> > new release, and with rpict, and see what's up with that.
> >
> > Mark
> >
> > On Tue, 27 Jan 2004, Greg Ward wrote:
> >
> > > Hi Mark,
> > >
> > > This is what you want:
> > >
> > > void brightfunc trans_mod
> > > 2 1-.6667/Rdot .
> > > 0
> > > 0
> > >
> > > trans_mod trans surf_dens
> > > 0
> > > 0
> > > 7 1 1 1 0 0 1 1
> > >
> > > The modifier will alter the specular transmission, and the trans has no
> > > diffuse component or specular reflection.  The reason transfunc didn't
> > > work for you was because the specularity you can modify is only used
> > > for light sources in that material.  You could use BRDTfunc, but the
> > > above is simpler.
> > >
> > > -Greg
> > >
> > > > From: Mark Stock <[email protected]>
> > > > Date: January 24, 2004 12:36:37 PM PST
> > > >
> > > > I am confused about the use of the transfunc. Function files took
> > > > me a little while to understand anyways, but what I can't figure out
> > > > is how to specify only a change in transmittance in a material.
> > > >
> > > >         mod transfunc id
> > > >         2+ brtd funcfile transform
> > > >         0
> > > >         6+ red green blue rspec trans tspec A7 ..
> > > >
> > > > I'd like to render a mesh object in "x-ray" form, but visualizing
> > > > its surface and not its volume. I'd like a material that diffuses
> > > > and reflects no light, and transmits light based on the "thickness"
> > > > of the surface (assuming that the object is a thin shell of fixed
> > > > thickness). I'd like the transmittance to be something like
> > > > 1.0-(const/Rdot), but when I try the following:
> > > >
> > > >         void transfunc meshcolor
> > > >         2 1.0-A5/Rdot .
> > > >         0
> > > >         6 0.5 0.5 0.5  1 0.66667 1
> > > >
> > > > I've tried several different values for the function, and everything
> > > > gives me a totally opaque object, or an "undefined function" error.
> > > > I'd like to get something like this:
> > > >
> > > > http://mark.technolope.org/vort3d/bd10/run168_first_sphere/burn1/
> > > > run05/save_0053.jpg
> > > >
> > > > Mark
> > >
> > > _______________________________________________
> > > Radiance-general mailing list
> > > [email protected]
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> > >
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>
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