add attachments to region()

rewrite "circle" attachment to use line intersection

attachments.scad

@@ -1522,7 +1522,7 @@ function _get_cp(geom) =
     )
     assert(type!="other", "Invalid cp value")
     cp=="centroid" ? centroid(geom[1])
-  : let(points = type=="vnf"?geom[1][0]:geom[1])
+  : let(points = type=="vnf"?geom[1][0]:flatten(force_region(geom[1])))
     cp=="mean" ? mean(points)
   : cp=="box" ? mean(pointlist_bounds(points))
   : assert(false,"Invalid cp specification");
@@ -1706,10 +1706,15 @@ function _find_anchor(anchor, geom) =
         let( 
             rr = geom[1],
             r = is_num(rr)? [rr,rr] : point2d(rr),
+            pos = approx(anchor.x,0) ? [sign(anchor.x)*r.x,0]
+                      : let(
+                             m = anchor.y/anchor.x,
+                             px = sign(anchor.x) * sqrt(1/(1/sqr(r.x) + m*m/sqr(r.y)))
+                        )
+                        [px,m*px],
             anchor = unit(point2d(anchor),[0,0]),
-            pos = point2d(cp) + v_mul(r,anchor) + point2d(offset),
-            vec = unit(v_mul(r,anchor),[0,1])
-        ) [anchor, pos, vec, 0]
+            vec = [r.y/r.x*pos.x, r.x/r.y*pos.y]
+        ) [anchor, point2d(cp+offset)+pos, vec, 0]
     ) : type == "rgn_isect"? ( //region
         assert(anchor.z==0, "The Z component of an anchor for a 2D shape must be 0.")
         let(
@@ -1727,7 +1732,10 @@ function _find_anchor(anchor, geom) =
                     n2 = vector_angle(anchor,n)>90? -n : n
                 )
                 if(!is_undef(isect) && !approx(isect,t[0])) [norm(isect), isect, n2]
-            ],
+            ]
+        )
+        assert(len(isects)>0, "Anchor vector does not intersect with the shape.  Attachment failed.")
+        let(
             maxidx = max_index(column(isects,0)),
             isect = isects[maxidx],
             pos = point2d(cp) + isect[1],
@@ -1736,8 +1744,7 @@ function _find_anchor(anchor, geom) =
     ) : type == "rgn_extent"? ( //region
         assert(anchor.z==0, "The Z component of an anchor for a 2D shape must be 0.")
         let(
-            rgn_raw = geom[1],
-            rgn = is_region(rgn_raw)? rgn_raw : [rgn_raw],
+            rgn = force_region(geom[1]),
             anchor = point2d(anchor),
             m = rot(from=anchor, to=RIGHT) * move(-[cp.x, cp.y, 0]),
             rpts = apply(m, flatten(rgn)),

drawing.scad

@@ -703,7 +703,7 @@ function arc(N, r, angle, d, cp, points, width, thickness, start, wedge=false, l
 module arc(N, r, angle, d, cp, points, width, thickness, start, wedge=false, anchor=CENTER, spin=0)
 {
     path = arc(N=N, r=r, angle=angle, d=d, cp=cp, points=points, width=width, thickness=thickness, start=start, wedge=wedge);
-    attachable(anchor,spin, two_d=true, path=path) {
+    attachable(anchor,spin, two_d=true, path=path, extent=true) {
         polygon(path);
         children();
     }

regions.scad

@@ -278,13 +278,16 @@ function force_region(poly) = is_path(poly) ? [poly] : poly;
 
 // Module: region()
 // Usage:
-//   region(r);
+//   region(r, [anchor], [spin], [cp]) { ... };
 // Description:
 //   Creates the 2D polygons described by the given region or list of polygons.  This module works on
 //   arbitrary lists of polygons that cross each other and hence do not define a valid region.  The
 //   displayed result is the exclusive-or of the polygons listed in the input. 
 // Arguments:
 //   r = region to create as geometry
+//   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#anchor).  Default: `"origin"`
+//   spin = Rotate this many degrees after anchor.  See [spin](attachments.scad#spin).  Default: `0`
+//   cp = Centerpoint for determining intersection anchors or centering the shape.  Determintes the base of the anchor vector.  Can be "centroid", "mean", "box" or a 2D point.  Default: "centroid"
 // Example(2D): Displaying a region
 //   region([circle(d=50), square(25,center=true)]);
 // Example(2D): Displaying a list of polygons that intersect each other, which is not a region
@@ -293,16 +296,18 @@ function force_region(poly) = is_path(poly) ? [poly] : poly;
 //       [square([60,10], center=true)]
 //   );
 //   region(rgn);
-module region(r)
+module region(r, anchor="origin", spin=0, cp="centroid")
 {
-    no_children($children);
     r = force_region(r);
     dummy=assert(is_region(r), "Input is not a region");
     points = flatten(r);
     lengths = [for(path=r) len(path)];
     starts = [0,each cumsum(lengths)];
     paths = [for(i=idx(r)) count(s=starts[i], n=lengths[i])];
+    attachable(anchor, spin, two_d=true, region=r, extent=false, cp=cp){
       polygon(points=points, paths=paths);
+      children();
+    }
 }
 
 
@@ -583,7 +588,7 @@ function region_parts(region) =
 
 // Function&Module: linear_sweep()
 // Usage:
-//   linear_sweep(region, height, [center], [slices], [twist], [scale], [style], [convexity]);
+//   linear_sweep(region, height, [center], [slices], [twist], [scale], [style], [convexity]) {attachments};
 // Description:
 //   If called as a module, creates a polyhedron that is the linear extrusion of the given 2D region or polygon.
 //   If called as a function, returns a VNF that can be used to generate a polyhedron of the linear extrusion
@@ -630,7 +635,7 @@ function region_parts(region) =
 //   mrgn = union(rgn1,rgn2);
 //   orgn = difference(mrgn,rgn3);
 //   linear_sweep(orgn,height=20,convexity=16) show_anchors();
-module linear_sweep(region, height=1, center, twist=0, scale=1, slices, maxseg, style="default", convexity, anchor_isect=false, anchor, spin=0, orient=UP, cp="centroid", anchor="origin") {
+module linear_sweep(region, height=1, center, twist=0, scale=1, slices, maxseg, style="default", convexity, anchor_isect=false, spin=0, orient=UP, cp="centroid", anchor="origin") {
     region = force_region(region);
     dummy=assert(is_region(region),"Input is not a region");
     anchor = center ? "zcenter" : anchor;