Hi Vidar,

I looked into my books about bezier patches and came to following
conclusion (I am not a expert for this!). The control points
b,c,e,f,g,h,i,j,k,l,n and o are *not* vertices of the bicubic patch (if
I am wrong about this assumption, please tell me!) but *real* control
points. So the points e and f should give the derivative of the curve at
this position. Here a small figure of a cut from e to h through the
patch.


                      f 
                     /  *****      g
                    / **     ***   `
                   /**          *** \
                  /*               **`
                 /*                  *\
                 e                     h

The * show the patch. The same should work for the combinations b-f,
j-n, c-g, ...
Just a vague hint as you asked for ;).

Marc

PS.: I like your idea for a sPatch like utility for Linux!

-- 
Marc Schimmler
Institut fuer Computeranwendungen
Universitaet Stuttgart

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