If N instances are given, it is theoretically possible to use N-1 anchor origins to define a deformation that would result in the N given forms at the corresponding aspect ratio factors. Just as in curve fitting, we would not fit a (n-1)th degree polynomial to a set of n points because of the over-crookedness of the resultant curve and the lack of localized control over the curve. Instead of determining the multi-level anchor origins which are the coefficients of the two continuous parametric equations, we could also employ piecewise continuous anchoring. In this case, the anchor origins (coefficients of the piecewise continuous parametric equations) can be easily determined from the neighbourhood picture instances. In the Skeletal Draw system, a Catmull-Rom spline interpolation scheme is employed.
Figure 11: Two stylish cartoon figures drawn with skeletal strokes.
The amount of information that needs to be stored for a skeletal stroke is small. For a stroke definition it is merely the original picture plus the original aspect ratio of the stroke (the ratio of length of reference backbone to reference thickness). If the points are anchored, the list would include the order of anchoring and the corresponding anchor origins.
For a stroke application, only the application path, its width (and other optional parameters) and its reference to a stroke definition is recorded. If the definition of a stroke is modified, the appearance of all the stroke applications referring to that stroke would reflect the changes immediately on redraw.
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