[Radiance-general] Transparent textures (again)

[Axel Jacobs]

Hi Greg,

> The mixpict primitive uses the indicated function of the red, green and
> blue channels of an image to determine how much of one material to use
> versus another.  One of these materials may be "void", which I
> recommend instead of the "glass" primitive that you're using in your
> current example.  A "void" material is the same as a perfectly
> transparent surface, which glass is not.  I would also recommend using
> "glow" instead of plastic to show up your falsecolor lines as something
> not truly belonging to the scene.

All this makes sense to me.

> 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.

> 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.

> 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.

You've been a great help

Axel