Wasn't it sumdumguy who wrote:
>Mike Williams <nos### [at] econymdemoncouk> wrote:
>> Wasn't it sumdumguy who wrote:
>> >This is more or less a math question not syntax question. Still, I 
>> >have killed
>> >many hours on this and so maybe someone has an idea.
>> >Say I have an isosurface:
>> >
>> >
>> >#declare  P = function {x*x + y*y + z*z - 1}
>> >
>> >isosurface {
>> >        function {P(x*2,y*(1.05-y/6),z*2)}
>> >        threshold 1
>> >        accuracy 0.001
>> >        max_gradient 200
>> >        contained_by{sphere{<0,0,0>,3}}
>> >        pigment {rgbt <0,1,0>}
>> >}
>> >
>> >This gives a stretched sphere where one side is squashed and the other
>> >is more sharp. Now what I want to do is to modify this isosurface so that
>> >there is also a bump on the surface, kind of like a wart on the nose.
>> >Any ideas on how to do this would be appreciated.
>>
>> The way I'd do it is:
>>
>> First: Eliminate the Threshold value by subtracting 1 in the function {}
>>         function {P(x*2,y*(1.05-y/6),z*2) -1}
>>
>> Then: Create a separate isosurface in the right location. It's much
>> easier to design this as a separate isosurface and then blob it onto the
>> nose later.
>>       isosurface {
>>         function {P(x*2,y*(1.05-y/6),z*2) -1}
>>         accuracy 0.001
>>         max_gradient 200
>>         contained_by{sphere{<0,0,0>,3}}
>>         pigment {rgbt <0,1,0>}
>>       }
>>       isosurface {
>>         function {P(x*4+1,y*4,z*4+2) -1}
>>         accuracy 0.001
>>         max_gradient 100
>>         contained_by{sphere{<0,0,0>,3}}
>>         pigment {rgbt <1,0,0>}
>>       }
>>
>> Once that's looking reasonable: Multiply the two functions together and
>> subtract a small constant. The smaller the constant, the sharper will be
>> the blending between the two isosurfaces. You may need to increase
>> max_gradient.
>>
>> #declare  P = function {x*x + y*y + z*z - 1}
>>
>> #declare  P1 = function {P(x*2,y*(1.05-y/6),z*2) -1}
>> #declare  P2 = function {P(x*4+1,y*4,z*4+2) -1}
>>
>> isosurface {
>>         function {P1(x,y,z)*P2(x,y,z) -0.03}
>>         accuracy 0.001
>>         max_gradient 5950
>>         contained_by{sphere{<0,0,0>,3}}
>>         pigment {rgbt <0,1,0>}
>> }
>>
>> --
>> Mike Williams
>> Gentleman of Leisure
>
>Ah, so it seems I have the master's attention. So before going any 
>further, many
>thanks for your isosurface tutorial, it has been a terrific resource.
>
>Now I tried what you have suggested before and got very weird results. Your
>reply here has helped me understand where the problem was. You see, I was
>really trying to do something like so:
>
>function {P1(x,y,z)*P2(x,y,z)+f_noise3d(x*10, y*10, z*10)*0.3-0.03}
>
>and when I add noise (values straight from the tutorial here, it creates a
>problem: the joint shape partly disappears.
>And I do not think it has to do with max_gradient. Rather it seems to be due to
>the noise function going above threshold. Any suggestions for making this shape
>wrinkly?

Going this route, you have to apply the noise to the individual 
functions, not to the smoothness parameter:

#declare  P = function {x*x + y*y + z*z - 1}
#declare  N = function {f_noise3d(x*10, y*10, z*10)*0.3}

#declare  P1 = function {P(x*2,y*(1.05-y/6),z*2) -1 + N(x,y,z)}
#declare  P2 = function {P(x*4+1,y*4,z*4+2) -1 + N(x,y,z)}

isosurface {
         function {P1(x,y,z)*P2(x,y,z) -0.03}

This also allows for the possibility of having different wrinkles on the 
wart.

-- 
Mike Williams
Gentleman of Leisure

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