>Given that you know the total length you can use 2*pi*r (perimeter of a
>circle) and the fact that  2*pi*r*360/angle = length

This is only true in the limit as the number of characters approaches 
infinity.  He's only got the lengths of the chords, not of the arcs.
The length of a chord is 2*r*sin(angle/2).  So the equation is:

   _ n
  \       -1
   > 2*sin  (chord  / (2*r)) = 360 (or 2*pi, if you use radians)
  /_              i
    i=1

And he's hoping to find r.  That doesn't look very easy to me.  I think
the only solution might be an iterative one.  Your answer gives a good
lower bound for r; I'm not sure what a good upper bound would be.

I'm also not sure this is the right group for this question; he might 
find better answers in .advanced-users.

Also, as an aside to the original poster, how about writing this routine 
as a macro using min_extent and max_extent instead of modifying truetype.c?  
The result will be the same without having to make a new patch, and you
might even be able to offer more options (such as an optional angle
that can be used to rotate each character around the x axis before moving
it to its final position, making a cone shape or a cylinder instead of a 
flat circle)

-- 
These are my opinions.  I do NOT speak for the POV-Team.
The superpatch: http://www2.fwi.com/~parkerr/superpatch/
My other stuff: http://www2.fwi.com/~parkerr/traces.html

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