"Bald Eagle" <cre### [at] netscapenet> wrote:
>
> The other thing that helps to work this all out in your head is to not delete
> code that doesn't work.   Otherwise you wind up coding the same mistakes over
> and over again.
>
>..That way you have a running documentation of what you've tried, ..., why it
> failed, what worked, etc. Heck, post it here, so
> that people struggling with the same issues can follow along and really
> see how one goes from fail to success...

Well, since you mentioned it... :-)

[more off-topic stuff, sorry!]
In my current real scene, I'm using the 'object pattern' to make an isosurface
shape, necessarily using functions. Here is a somewhat simplified version of a
problem I had:

#declare OBJ_PATTERN_FUNC = function{pigment{object{MY_OBJECT rgb 0 rgb 1}}}
#declare PIG_DISTORTION_FUNC = function{pigment{bumps scale .2}}
#declare MAG = 1.5; // the magnitude of the bumps distortion to be added

This is how I originally wrote my main function:

isosurface{function{
1 - (OBJ_PATTERN_FUNC(
x + MAG*PIG_DISTORTION_FUNC (x,y,z).x - .5*MAG,
y + MAG*PIG_DISTORTION_FUNC (x,y,z).y - .5*MAG,
z + MAG*PIG_DISTORTION_FUNC (x,y,z).z - .5*MAG
     ).gray)
     } ... }

This worked-- but the resulting bumps distortion had a spatial 'skew' aligned
along <1,1,1>, which *finally* became understandable because I was using full
(x,y,z) in all 3 inner functions. (I had to do that to solve other problems that
I ran into, up to this point.) But substituting 0.0 for the appropriate
'un-needed' x,y,z arguments resulted in *very* strange isosurface effects.

So I came up with this solution, which nicely fixed the skew--by subtracting the
'offending' arguments from 1.0. But I have NO idea why it works. I finally
arrived at it through pure chance and desperation:

isosurface{function{
1 - (OBJ_PATTERN_FUNC(
x + MAG*PIG_DISTORTION_FUNC (x,1-y,1-z).x - .5*MAG,
y + MAG*PIG_DISTORTION_FUNC (1-x,y,1-z).y - .5*MAG,
z + MAG*PIG_DISTORTION_FUNC (1-x,1-y,z).z - .5*MAG
     ).gray)
     } ...}

Maybe this is a special-case solution because of the object pattern scheme? I
don't know.

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