"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> Vertical incisions could be done as a stretched pigment, and fractures as
> crackle. I'll try it out tonight and see if it works. Preferential weathering
> at corners and edges is of course more realistic, but I'm not sure how it could
> be done. A translated turbulent wood could work on one edge, but not many...
> hmm, I shall ponder.

Here's my thoughts on preferential weathering:

1) Go over the object with a coarse grid and store the radii.  Store these in an
array.

2) Go over the array and calculate the second derivative or some other measure
of curvature.  Wikipedia should have the Laplacian operator.  Just take r
constant.

3) Of course sharp edges will only have a local effect, so filter the data with
a Gaussian function.  Just calculate an average of every point with its
neighbors, weighted by a Gaussian distribution.  Very simple.

4) Now go back over it with your algorithm.  Same type of grid, so if it's finer
just interpolate the curvature onto the fine grid.  Areas with zero curvature
get the original function.  Areas with high curvature get the full
perturbation.

Think of a cube.  The edges contribute to the curvature of all the points around
them so you get smooth faces and weathered edges without any discontinuities.

Just a thought.

 - Ricky

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