Michael Andrews <m.c### [at] readingacuk> wrote:
> #declare REBUILD = pigment { ... }

> how do you define REBUILD to give the same pigment as PIG, based on
> FNPIG?

  AFAIK, it's not currently possible.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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Warp wrote:
> 
> Michael Andrews <m.c### [at] readingacuk> wrote:
> > #declare REBUILD = pigment { ... }
> 
> > how do you define REBUILD to give the same pigment as PIG, based on
> > FNPIG?
> 
>   AFAIK, it's not currently possible.
>
Well, yes it is possible (see the picture I just posted in Gilles' fast
cloud thread on p.b.i) but the method I've found is pretty brute-force
and klutzy. I was hoping somone would have a bright idea on how to do it
better than I have. That's why I haven't posted my attempt yet - I don't
want to predispose folks to look at the problem from one direction.

If noone comes up with anything by the weekend I'll post my solution.

Bye for now,
	Mike Andrews.

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On Thu, 11 Apr 2002 13:18:26 +0100, Michael Andrews <m.c### [at] readingacuk>
wrote:
> If noone comes up with anything by the weekend I'll post my solution.

layers ?

ABX

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--
__________________
 RAY
"Michael Andrews" <m.c### [at] readingacuk> wrote in message
news:3CB### [at] readingacuk...
> Hi Folks,
>
> I was playing with Gilles' cloud pigment and hit a problem: what is the
> best (ie fastest rendering) way to reproduce an arbitrary pigment from
> it's function?
>
> For example, given
>
> #declare PIG = pigment { bozo colour_map {[0.2 rgbf 1][0.5 rgb
> y*1.3][0.7 rgb x transmit 1] } }
> #declare FNPIG = function { pigment { PIG } }
>
> #declare REBUILD = pigment { ... }
>
> how do you define REBUILD to give the same pigment as PIG, based on
> FNPIG?
>
> Normally it's just a matter of
>
> #declare REBUILD = pigment {
>   average
>   pigment_map {
>     [1 function { FNPIG(x,y,z).x } colour_map {[0 rgb 0][1 rgb 3*x]} ]
>     [1 function { FNPIG(x,y,z).y } colour_map {[0 rgb 0][1 rgb 3*y]} ]
>     [1 function { FNPIG(x,y,z).z } colour_map {[0 rgb 0][1 rgb 3*z]} ]
>   }
> }

would #declare REBUILD = pigment {function {FNPIG}}; work

> but with filter, transmit or colours with values greater than one this
> doesn't work.
>
> I've come up with one structure which works, but is very slow for how I
> am using it.
>
> So, I was hoping someone can come up with a better method. Any takers?
Yes ;-)

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#declare REBUILD = pigment {
average
pigment_map {
   [1 function{FNPIG(x,y,z).red}     colour_map {[0 rgbft<-2, 0, 0, 0,
0>][1 rgbft< 3, 0, 0, 0, 0>]}]
   [1 function{FNPIG(x,y,z).green}   colour_map {[0 rgbft< 0,-2, 0, 0,
0>][1 rgbft< 0, 3, 0, 0, 0>]}]
   [1 function{FNPIG(x,y,z).blue}    colour_map {[0 rgbft< 0, 0,-2, 0,
0>][1 rgbft< 0, 0, 3, 0, 0>]}]
   [1 function{FNPIG(x,y,z).filter}  colour_map {[0 rgbft< 1, 1, 1, 0,
0>][1 rgbft< 1, 1, 1, 5, 0>]}]
   [1 function{FNPIG(x,y,z).transmit}colour_map {[0 rgbft< 1, 1, 1, 0,
0>][1 rgbft< 1, 1, 1, 0, 5>]}]
 }
}

This seems to work. I'm fairly certain the math is OK, but I still have
to mull it over. Seemed to worked in a visual comparison test with the
original and rebuilt pigments side by side.

Michael Andrews wrote:
> 
> Warp wrote:
> >
> > Michael Andrews <m.c### [at] readingacuk> wrote:
> > > #declare REBUILD = pigment { ... }
> >
> > > how do you define REBUILD to give the same pigment as PIG, based on
> > > FNPIG?
> >
> >   AFAIK, it's not currently possible.
> >
> Well, yes it is possible (see the picture I just posted in Gilles' fast
> cloud thread on p.b.i) but the method I've found is pretty brute-force
> and klutzy. I was hoping somone would have a bright idea on how to do it
> better than I have. That's why I haven't posted my attempt yet - I don't
> want to predispose folks to look at the problem from one direction.
> 
> If noone comes up with anything by the weekend I'll post my solution.
> 
> Bye for now,
>         Mike Andrews.

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...except it still will not work for color component values outside of
the range of 0 to 1 since the technique is limited by the color_map
index range. A workaround (if one knew beforehand the color range) would
involve scaling FNPIG by 1/[maximum expected color range] and setting up
the color_map entries to cover the maximum expected color range.

Abe

Abe wrote:
> 
> #declare REBUILD = pigment {
> average
> pigment_map {
>    [1 function{FNPIG(x,y,z).red}     colour_map {[0 rgbft<-2, 0, 0, 0,
> 0>][1 rgbft< 3, 0, 0, 0, 0>]}]
>    [1 function{FNPIG(x,y,z).green}   colour_map {[0 rgbft< 0,-2, 0, 0,
> 0>][1 rgbft< 0, 3, 0, 0, 0>]}]
>    [1 function{FNPIG(x,y,z).blue}    colour_map {[0 rgbft< 0, 0,-2, 0,
> 0>][1 rgbft< 0, 0, 3, 0, 0>]}]
>    [1 function{FNPIG(x,y,z).filter}  colour_map {[0 rgbft< 1, 1, 1, 0,
> 0>][1 rgbft< 1, 1, 1, 5, 0>]}]
>    [1 function{FNPIG(x,y,z).transmit}colour_map {[0 rgbft< 1, 1, 1, 0,
> 0>][1 rgbft< 1, 1, 1, 0, 5>]}]
>  }
> }
> 
> This seems to work. I'm fairly certain the math is OK, but I still have
> to mull it over. Seemed to worked in a visual comparison test with the
> original and rebuilt pigments side by side.
> 
> Michael Andrews wrote:
> >
> > Warp wrote:
> > >
> > > Michael Andrews <m.c### [at] readingacuk> wrote:
> > > > #declare REBUILD = pigment { ... }
> > >
> > > > how do you define REBUILD to give the same pigment as PIG, based on
> > > > FNPIG?
> > >
> > >   AFAIK, it's not currently possible.
> > >
> > Well, yes it is possible (see the picture I just posted in Gilles' fast
> > cloud thread on p.b.i) but the method I've found is pretty brute-force
> > and klutzy. I was hoping somone would have a bright idea on how to do it
> > better than I have. That's why I haven't posted my attempt yet - I don't
> > want to predispose folks to look at the problem from one direction.
> >
> > If noone comes up with anything by the weekend I'll post my solution.
> >
> > Bye for now,
> >         Mike Andrews.

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"RAY" <RAY### [at] yahoocom> wrote in message news:3cb73511@news.povray.org...
>
>
> --
> __________________
>  RAY
> "Michael Andrews" <m.c### [at] readingacuk> wrote in message
> news:3CB### [at] readingacuk...
> > Hi Folks,
> >
> > I was playing with Gilles' cloud pigment and hit a problem: what is the
> > best (ie fastest rendering) way to reproduce an arbitrary pigment from
> > it's function?
> >
> > For example, given
> >
> > #declare PIG = pigment { bozo colour_map {[0.2 rgbf 1][0.5 rgb
> > y*1.3][0.7 rgb x transmit 1] } }
> > #declare FNPIG = function { pigment { PIG } }

Replace this with a five-parameter function:

#declare FNPIG = function(rd,gr,bl,ft,tr) { pigment { PIG } }

> >
> > #declare REBUILD = pigment { ... }
> >
> > how do you define REBUILD to give the same pigment as PIG, based on
> > FNPIG?
> >
> > Normally it's just a matter of
> >
> > #declare REBUILD = pigment {
> >   average
> >   pigment_map {
> >     [1 function { FNPIG(x,y,z).x } colour_map {[0 rgb 0][1 rgb 3*x]} ]
> >     [1 function { FNPIG(x,y,z).y } colour_map {[0 rgb 0][1 rgb 3*y]} ]
> >     [1 function { FNPIG(x,y,z).z } colour_map {[0 rgb 0][1 rgb 3*z]} ]
> >   }
> > }
>
> would #declare REBUILD = pigment {function {FNPIG}}; work

After replacing the FNPIG function, the simple declare should work:

#declare REBUILD = pigment { function(rd,gr,bl,ft,tr) {FNPIG}}

>
> > but with filter, transmit or colours with values greater than one this
> > doesn't work.
> >
> > I've come up with one structure which works, but is very slow for how I
> > am using it.
> >
> > So, I was hoping someone can come up with a better method. Any takers?
> Yes ;-)
>
>

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David Wallace <dar### [at] earthlinknet> wrote:
> #declare REBUILD = pigment { function(rd,gr,bl,ft,tr) {FNPIG}}

  Have you actually tried that?

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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"Michael Andrews" <m.c### [at] readingacuk> wrote in message
news:3CB45A4F.413CA07F@reading.ac.uk...

>

>
> >     [1 function { FNPIG(x,y,z).filter } colour_map {[0 rgb 0][1 filter
5]} ]
>
> Sorry, no, this is always black :-/
>
> I hadn't thought of trying this way though ...
>
> Bye for now,
> Mike Andrews.

I tried a 5-parameter function thinking that the results would be truncated
otherwise... POV rejected it as an error:
"Function parameters for pigment functions are not allowed."

I suspect that your problem is that any 5D color vector that is interpreted
in a function block is truncated to 3D RGB form.  If that's so then you're
SOL.

Post a reply to this message

In article <3cb797fa@news.povray.org> , "David Wallace" 
<dar### [at] earthlinknet> wrote:

> I tried a 5-parameter function thinking that the results would be truncated
> otherwise... POV rejected it as an error:
> "Function parameters for pigment functions are not allowed."
>
> I suspect that your problem is that any 5D color vector that is interpreted
> in a function block is truncated to 3D RGB form.  If that's so then you're
> SOL.

No, this is not the case.  The error message simply says you may not specify
function parameters for functions with a fixed parameter list, which is
explained in the documentation.


    Thorsten

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