add vnf_hull() and hull_region()

regions.scad

@@ -1396,4 +1396,39 @@ module exclusive_or() {
 }
 
 
+
+// Function&Module: hull_region()
+// Synopsis: Compute convex hull of region or 2d path
+// SynTags: Geom, Path
+// Topics: Regions, Polygons, Shapes2D
+// Usage:
+//    path = hull_region(region);
+//    hull_region(region);
+// Description:
+//   Given a path, or a region, compute the convex hull
+//   and return it as a path.  This differs from {{hull()}} and {{hull2d_path()}} which
+//   return an index list into the point list.  As a module invokes the native hull() on
+//   the specified region.  
+// Arguments:
+//   region = region or path listing points to compute the hull from.  
+// Example(2D, NoAxes):
+   data = [star(id=10,od=20,n=9),
+           right(30, star(id=12,od=25, n=7))];
+   stroke(data);
+   stroke([hull_region(data)],color="red");
+function hull_region(region) =
+  assert(is_path(region) || is_region(region))
+  let(
+      pts = is_region(region) ? flatten(region)
+                              : region,
+      order = hull2d_path(pts)
+  )
+  select(pts,order);
+
+module hull_region(region)
+{
+  hull()region(region);
+}
+
+
 // vim: expandtab tabstop=4 shiftwidth=4 softtabstop=4 nowrap

skin.scad

@@ -2958,13 +2958,13 @@ function associate_vertices(polygons, split, curpoly=0) =
 //       tex_size=[10,10]
 //   );
 // Example(3D): **"dimples"** (VNF) = Round divots.  Specify `$fn` to set the number of segments on the cone (will be rounded to a multiple of 4).  If you use $fa and $fs then the number of segments is determined for the original VNF scale of 1x1.  Giving `border=` specifies the horizontal width of the flat border region between the tile edges and the edge of the dimple.  Must be nonnegative and strictly less than 0.5.  Default: 0.05.  
-//   tex = texture("dimples");
+//   tex = texture("dimples", $fn=16);
 //   linear_sweep(
 //       rect(30), texture=tex, h=30, 
 //       tex_size=[10,10]
 //   );
 // Example(3D): **"dots"** (VNF) = Raised round bumps.  Specify `$fn` to set the number of segments on the cone (will be rounded to a multiple of 4).  If you use $fa and $fs then the number of segments is determined for the original VNF scale of 1x1.  Giving `border=` specifies the horizontal width of the flat border region between the tile edge and the edge of the dots.  Must be nonnegative and strictly less than 0.5.  Default: 0.05.
-//   tex = texture("dots");
+//   tex = texture("dots", $fn=16);
 //   linear_sweep(
 //       rect(30), texture=tex, h=30,
 //       tex_size=[10,10]

vnf.scad

@@ -1414,6 +1414,53 @@ function vnf_bend(vnf,r,d,axis="Z") =
    ) [new_vert,sliced[1]];
 
 
+
+// Function&Module: vnf_hull()
+// Synopsis: Compute convex hull of VNF or 3d path
+// Usage:
+//    vnf_hull = hull_vnf(vnf);
+//    hull_vnf(vnf,[fast]);
+// Description:
+//   Given a VNF or a list of 3d points, compute the convex hull
+//   and return it as a VNF.  This differs from {{hull()}} and {{hull3d_faces()}} which
+//   return just the face list referenced to the input point list.  Note that the point
+//   list that is returned will contain all the points that are actually used in the input
+//   VNF, which may be many more points than are needed to represent the convex hull.
+//   This is not usually a problem, but you can run the somewhat slow {{vnf_drop_unused_points()}}
+//   function to fix this if necessary.  
+// Arguments:
+//   region = region or path listing points to compute the hull from.
+//   fast = (module only) if input is a point list (not a VNF) use a fasterer cheat that may handle more points, but could emit warnings.  Ignored if input is a VNF.  Default: false.  
+// Example(3D,Big,NoAxes): Input is a VNF
+//   ellipse = xscale(2, p=circle($fn=48, r=3));
+//   pentagon = subdivide_path(pentagon(r=1), 20);
+//   vnf=path_sweep(pentagon, path3d(ellipse),
+//                  closed=true, twist=360*2);
+//   vnfhull = vnf_hull(vnf);
+//   vnf_polyhedron(vnf);
+//   move([10,10])
+//     vnf_polyhedron(vnfhull);
+// Example(2D, NoAxes): Input is a point list
+//   h=helix(l=40, turns=1, r=8);
+//   color("red")move_copies(h)
+//     sphere(r=0.5,$fn=12);
+//   vnf_polyhedron(vnf_hull(h));
+function vnf_hull(vnf) =
+  assert(is_vnf(vnf) || is_path(vnf,3),"Input must be a VNF or a 3d path")
+  let(
+      pts = is_vnf(vnf) ? select(vnf[0],unique(flatten(vnf[1])))
+                        : vnf,
+      faces = hull3d_faces(pts)
+  )
+  [pts, faces];
+
+module vnf_hull(vnf, fast=false)
+{
+  if (is_vnf(vnf)) hull()vnf_polyhedron(vnf);
+  else hull_points(vnf, fast);
+}  
+    
+
 // Section: Debugging Polyhedrons
 
 /// Internal Module: _show_vertices()