[Radiance-general] Transparent textures (again)

[Greg Ward]

Hi Axel,

Beware, quick response ahead:

> From: "Axel Jacobs" <a.jacobs at londonmet.ac.uk>
> Date: March 3, 2005 12:05:22 PM PST
>> void colorpict fc_val
>> 7 red green blue sp.pic fc.cal fc_u fc_v
>> 0
>> 0
>
> Since the black is going to be removed anyhow, we could use the normal
> picture.cal like so:
>
> void colorpict fc_val
> 15 red green blue sp.pic picture.cal pic_u pic_v -s 4 -rz -90 -t .5 
> 5.5 0
> 0
> 0
>
> Doesn't seem to make any diff.

True, but they you won't be able to change the definitions of fc_u and 
fc_v and have the colorpict line up with the mixpict.  I think it's 
better to use the same file for clarity.

>> fc_val glow fc_glow
>> 0
>> 0
>> 4 1 1 1 0
>
> The glow intensity would have to be adjusted to 'look nice' with the
> ambient light in the scene, right? It looks better in my scene with a 
> glow
> of 2 2 2 0 or 3 3 3 0.

Yes, you are right to adjust it for your scene -- should have mentioned 
that.

>> void mixpict mp
>> 7 fc_glow void nonzero sp.pic fc.cal fc_u fc_v
>> 0
>> 0
>> --------
>> The file "fc.cal" looks like so:
>>
>> { Use false color contour image as selector }
>> nonzero(r,g,b) = if(max(r,max(g,b))-FTINY, 1, 0);
>> fc_u = Px;
>> fc_v = Py;
>> ------
>
> Exactly what I was missing. The FTINY thing is in case the black isn't
> really black, isn't it? Or is it for internal rounding errors etc. 
> With my
> perfectly back background (you wished you had this in a lighting 
> lab...),
> I could drop this. Well, I did remove it and it still works, anyhow.

The FTINY is in there as a guard against rounding errors, and I 
wouldn't recommend removing it.  It may work on your compile on your 
machine, but another machine may not.

-Greg