".nefdbg" extension to dump debug info on CGALNefPolyhedron3+SphereMaps

[donbright]

This is a small patch to allow an easier dump of already existing debug code for CGAL Nef Polyhedrons. It also adds some code to dump Sphere Map information as well.

It allows the ".nefdbg" file extension that will trigger a dump of an SVG file containing detailed information about the Nef Polyhedron and it's associated Vertex Sphere Maps. This will make it a bit easier to debug Nef Polyhedron issues in the future. The feature is left as an "undocumented" feature so that users will not rely on the format and it can change as needed.

The SVG file has dual use - it contains very detail information as 'comments' within the text file, while the file itself can be opened in a web browser to view a graphic picture of the Nef Polyhedron faces.

Here is an example of the svg text for a vertex sphere map

<!-- vertex sphere map begin. vertex counter is 1
     vertex coordinates: -32.5,16.9177,-23.3125-->
  vertex sphere map info
  number of svertices: 3
  number of shalfedges: 6
  number of shalfloops: 0
  number of sfaces: 2
  number of sface cycles: 2
  connected_components: 1
  integrity check...(asserts if not OK)
 the sface cycles of sface 0 start with an
  shalfedge from 0,0,47.744 to 0,-37.652,0
 the sface cycles of sface 1 start with an
  shalfedge from 0,-37.652,0 to 0,0,47.744

  vertex sphere map end -->

Here is a snippet showing a HalfFacet visit (part of a Volume visit)

<!-- Halffacet visit. Mark: 1 -->
   <!-- Halffacet cycle begin: -->
    <!-- Body contour:--> 
     <!-- -32.5,16.9177,-23.3125 -->
     <line x1="130.71" y1="307.358" x2="43.8203" y2="394.248"  stroke="gold" />
     <!-- -30,16.9177,-23.3125 -->
     <line x1="142.12" y1="307.358" x2="130.71" y2="307.358"  stroke="gold" />
     <!-- -30,-20.7343,-23.3125 -->
     <line x1="55.2304" y1="394.248" x2="142.12" y2="307.358"  stroke="gold" />
     <!-- -32.5,-20.7343,-23.3125 -->
     <line x1="43.8203" y1="394.248" x2="55.2304" y2="394.248"  stroke="gold" />
   <!-- Halffacet cycle end -->
  <!-- Halffacet visit end -->

The SVG file can also be loaded in a web browser, where it currently looks like this:

[kintel]

Would it make sense to also add a ".nef3" output as well, for easier stand-alone testing with CGAL demos/examples?

[donbright]

Hmmm... Is ".nef3" the Official CGAL format for Nef Polyhedrons ?

[donbright]

Im looking at http://doc.cgal.org/latest/Nef_3/index.html#Nef_3File .... ?? I think I can add that without too much trouble . . . . You just want to add another extension that is basically '.nef3' ?

[kintel]

Looks like CGAL is using ".nef3": https://github.com/CGAL/cgal/tree/master/Nef_3/test/Nef_3/data

I've also implemented .nef3 support for some test apps: https://github.com/openscad/openscad/blob/master/cgal/decompose.cpp

[donbright]

ok i added .nef3 as an output filename, and tested with "decompose" (with a patch or two for linux/g++)

it was uhm.... interesting.... looks like 1970s wallpaper...

[TakeItAndRun]

Nice, real nice.

(the picture)

2015-10-27 3:11 GMT+01:00 don bright notifications@github.com:

ok i added .nef3 as an output filename, and tested with "decompose" (with
a patch or two for linux/g++)

it was uhm.... interesting.... looks like 1970s wallpaper...

[image: delme]
https://cloud.githubusercontent.com/assets/896858/10747668/f24d4038-7c25-11e5-86fd-cc3ad9163e4c.png

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[kintel]

@donbright Btw., in case you didn't know; it's possible to openscad cube.scad --render=cgal -o out.nef3 - makes it possible to easier test CGAL corner cases without having to add csg ops just to force a round-trip through CGAL.