Hi,

I recently posted the thing about text paths.  I've been able to extract
the path data from TrueType fonts.  As far as I've read, this is
quadratic b-spline data.  And I've been able to represent these paths
in a tcl/tk app, which natively uses quadratic b-splines, and everything
looks beautiful.

But when I try to represent these paths in povray using the sphere_sweep
b-spline, things aren't working out so well.  Of course at first I just
thought this was because povray uses cubic b-splines.  And it should be
straightforward to convert a quadratic b-spline into a cubic b-spline.  

But I'm not having any success yet.

I can convert the quadratic b-spline into a set of bezier curves.  And
I can overlay the bezier curves in tcl/tk on top of the quadratic
b-spline curve and they match perfectly.

I thought (and maybe this is where I'm wrong) that a cubic b-spline curve
was nothing more than a bunch of bezier curves strung together with
endpoints joined (and actually removed, being represented by the midpoints
of adjacent control points).  But this does not yield a curve that matches
the original letter shape.  It's close, but the curves are too sharp near
the control points and too flat near the mid-points.

Is my assumption about the relationship between cubic b-splines and
beziers wrong?  Or is povray's sphere_sweep b_spline just some other kind
of curve?  Or am I on the right track, but just making some mistake in
representing the data in the appropriate order?

Thanks,

     tom

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