[Radiance-general] Re: Transparent Textures in Radiance

[Greg Ward]

Hi Lars,

Using mixpict to achieve transparency can be done in one of two ways.  
The preferred method is to specify "void" as one of the alternate 
materials, either foreground or background, and where the mixpict 
evaluates to 1 (or 0), the surface will be disregarded.  The other 
alternative is to specify a trans material with the following 
parameters:

void trans passthru
0
0
7 0 0 0 0 0 1 1

If I remember right, this will send the ray straight through without 
any alterations, though it is slightly more expensive than using the 
"void" modifier.  For more information, check out this entry in the old 
Radiance digests:

	http://radsite.lbl.gov/radiance/digests_html/v3n0.html#OPACITY_MAPPING

-Greg

> From: "Lars O. Grobe" <grobe at gmx.net>
> Date: July 19, 2004 12:02:35 PM PDT
>
> Hi,
>
> this thread is rather old, however I just came to the same point. No, 
> not to a glass of beer, but to the adventure of using a new modifier 
> type:
>
> (12/02/03) Peter Apian-Bennewitz wrote:
>> R Gillibrand wrote:
>>
>>> Hi All,
>>>
>>> Is it possible to have transparent textures in the mesh primitive? I 
>>> have a student who wants to map a logo around a beer glass and I 
>>> can’t find a way to do so but hope to be proved wrong!
>>>
>>
> [...]
>>    void mixpict mp
>>    15 mp1 mp2 digital1 sp.pic picture_UV.cal tpic_u tpic_v ...
>>    0
>>    0
>
> I understand mp1 and mp2 (the modifiers to mix), digital1 means there 
> is 1/0 substitution, where is it defined, or do I have to define this 
> function? Than sp.pic as the picture, ok, with white meaning 
> foreground mod, black background? Finally picture_UV.cal, I guess you 
> wanted to show the need of a beer glass mapping func ;-)?
>
> All I know about mixpict is from ray.pdf, is there any other source?
>
> I have some kind of mosaic that I don't want to model geometrically. 
> It consists of three different materials. I have material definitions 
> (plastic) of all three. Can I use mixpict to create some kind of 
> "mask" in radiance? Is it possible to use a mixpict modifier as a 
> background in mixpict (I think I would have to do so if I want to 
> combine three, not two)? Finally - is it more adviseable to assemble 
> the mosaic in a bitmap editor (gimp, photoshop & co) and apply it by 
> using the colorpict modifier?