POV-Ray : Newsgroups : povray.general : transparency gradient? : Re: transparency gradient? Server Time
12 Aug 2024 11:16:57 EDT (-0400)
  Re: transparency gradient?  
From: Spider
Date: 15 Feb 1999 19:13:21
Message: <36C8B6D8.23C34458@bahnhof.se>
Ken wrote:
> 
> Marc Schimmler wrote:
> >
> > I'm just wondering if it is possible to make an object which
> > transparency that changes with it's height?
> > Imagine a cylinder which is nearly total transparent at it's bottom and
> > and fully opaque at the top.
> >
> > Any help appreciated from indenters as well as from non-indenters!!! ;-)
> >
> > Thanks in advance,
> > Marc
> 
> Note: for the purpose of this response I am going to refer to
> transperancy as clear just because it's easier to type :)
> 
> You are on the right track with the gradient idea. The thing you
> have to watch out for with mixing solid pigments with clear pigments
> is that the pattern function will blend the solids in with the clear
> parts making them much less clear. TO get around this you have to
> carefully design you color map around this limitation.
> 
> An untested example:
> 
>                               cylinder{
>                              <0,-1,0>,
>                             <0,1,0>,
>                            1
>                           pigment{
>                          gradient y
>                        color_map{
>            [0.0 rgbf<1,1,1,1.0>]
>            [0.0 rgbf<1,1,1,1.0>]
>            [0.2 rgbf<1,1,1,0.8>]
>            [0.2 rgbf<1,1,1,0.8>]
>            [0.4 rgbf<1,1,1,0.6>]
>            [0.4 rgbf<1,1,1,0.6>]
>            [0.6 rgbf<1,1,1,0.4>]
>            [0.6 rgbf<1,1,1,0.4>]
>            [0.8 rgbf<1,1,1,0.2>]
>            [1.8 rgbf<1,1,1,0.2>]
>            [1.0 rgbf<1,1,1,0.0>]
>                                  }
>                       translate -.5
>                                     }
>                                       }
> 
> How is my indenting now people ?
interesting. it's.... Different.


> 
> Anyway if you study the example you will see that I have bracketed each
> map entry with a duplicate entry. This causes a sharp demarcation of
> pigment color, clearness, and stops the bleeding from adjacent entries.
> This example may be too sharp in it's cutoff points for what you want.
> To correct this let each value in the color map entry extend a bit
> higher than the one before it. If that doesn't work for you then just
> start randomly playing with values and see what happens. Exploration
> is a mighty powerfull teacher and there are few substitutions that will
> replace it.

Well, that is if you want it to be filtering the light.

Easier would be transparent.(transmit)
pigment { 
  gradient y
  tubulence <0.3,1.2,0.2>
  octaves 3600 //ou _are_ patient, aren't you *smile*
  omega 1/24
  lambda 0.4
  colour_map {
    [0.0 colour rgbt <0.7,0.7,1,0>]
    [1.0 colour rgbt <0.7,0.7,1,1>]
  }
}

//Spider
"42"
http://www.bahnhof.se/~spider/


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