I want to create a shape that goes from

((x+R)*(x-R) & (z+R)*(z-R))

at a specified y height

to

(sqrt(x^2+z^2)-R)

at another specified height in y.

How can I do this? The idea is that I bind the thing with box
{-<R,H1,R>,<R,H2,R>}, so that it goes from square to circle. Perhaps, if
there is a way, could someone explain how to "gradient" between other
shapes? Say, a triangle or a star?

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TonyB wrote:

> How can I do this? The idea is that I bind the thing with box
> {-<R,H1,R>,<R,H2,R>}, so that it goes from square to circle. Perhaps, if
> there is a way, could someone explain how to "gradient" between other
> shapes? Say, a triangle or a star?

To "gradient" between shapes all just join the formulas like this :
f = f1*(1-y) + f2*y
so that the shape starts at f1 and ends at f2 when y goes from 0 to 1
(adapt to your own y values)
for instance :
isosurface {
  function {(abs(x)+abs(z))*(1-y)+(x^2+y^2+z^2)*y}
  contained_by {box {<-1,0,-1>,<1,1,1>}}
  eval
  sign 1
  threshold 1
  pigment{Red}
}

starts as a cube and ends as a sphere

G.

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I was this close to getting it figured out on my own: instead of 1-y I wrote
y-1 and instead of adding the two functions I was trying out everything
else. Last one I had was &. Thanks a bunch, Gilles. :)

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