I've dug into the normal{} block facets perturbation code a little. I'll 
note a few things and then show the initial set of related keyword 
changes I hope makes facets simpler to use in yuqk.

These notes which apply to official releases and the yuqk fork:

1) Spatial modifiers (ie scale 0.5) as used within the normal{} block 
affect only the flat form.

2) The 'coords' keyword is effectively 'bump_size', thought it only 
affects the flat form.

3) In news to me, there exist already a fully functioning 'metric' 
keyword for both forms. I'm not aware of this being documented anywhere?

4) It was noted somewhere on these news groups that facets replaces the 
normal rather than perturbs it, but this is only true for the 
spherically / curved surface oriented version of facets.

5) The internal code used a crackle implementation but it is an older 
and (by comment at least) slower version than the current crackle 
pattern code implementation.

6) The spherical form is best applied around the origin then transformed 
for use.

7) Both patterns are sensitive to extreme scaling around the default of 
0.1. The spherical form more so than the flat one.

-----------

The attached image reflects the result of the top set of normal{} block 
facets specifications for recent official releases of POV-Ray as well as 
the bottom set of four specifications reflecting the keyword changes 
being adopted for release R15 of yuqk. The core facet implementation has 
not yet been changed.

The aim was to quickly try out the already implemented 'metric' keyword 
code and the keyword changes.

  //--- For official releases
  //facets coords 0.8 size 0.1 metric  0+(frame_number-1)*1.0
  //facets coords 0.8 size 0.1 metric -2+(frame_number-1)*0.5
  //facets coords 0.0 size 0.1 metric  0+(frame_number-1)*1.0
  //facets coords 0.0 size 0.1 metric -2+(frame_number-1)*0.5

  //--- The version with yuqk's keyword changes
    facets type 0 ip_size 0.1
      ip_metric  0+(frame_number-1)*1.0 bump_size 0.8
  //facets type 0 ip_size 0.1
  //  ip_metric -2+(frame_number-1)*0.5 bump_size 0.8
  //facets type 1 ip_size 0.1
  //  ip_metric  0+(frame_number-1)*1.0
  //facets type 1 ip_size 0.1
  //  ip_metric -2+(frame_number-1)*0.5

Bill P.

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