doc fixes

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Adrian Mariano 2021-11-06 10:42:45 -04:00
parent 924421fa22
commit 4315b8c0b6

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@ -1,9 +1,11 @@
//////////////////////////////////////////////////////////////////////
// LibFile: regions.scad
// This file provides 2D boolean geometry operations on paths, where you can
// compute the intersection or union of the shape defined by point lists, producing
// a new point list. Of course, boolean operations may produce shapes with multiple
// components. To handle that, we use "regions" which are defined as lists of paths.
// This file provides 2D boolean set operations on polygons, where you can
// compute, for example, the intersection or union of the shape defined by point lists, producing
// a new point list. Of course, such operations may produce shapes with multiple
// components. To handle that, we use "regions" which are defined by lists of polygons.
// In addition to set operations, you can calculate offsets, determine whether a point is in a
// region and you can decompose a region into parts.
// Includes:
// include <BOSL2/std.scad>
//////////////////////////////////////////////////////////////////////
@ -16,30 +18,32 @@
// Section: Regions
// A region is a list of polygons meeting these conditions:
// .
// - Every polygon on the list is simpel, meaning it does not intersect itself
// - Every polygon on the list is simple, meaning it does not intersect itself
// - Two polygons on the list do not cross each other
// - A vertex of one polygon never meets the edge of another one except at a vertex
// .
// Note that this means vertex-vertex touching between two polygons is acceptable
// to define a region. Note, however, that regions with vertex-vertex contact usually
// cannot be rendered with CGAL.
// cannot be rendered with CGAL. See {{is_valid_region()}} for examples of valid regions and
// lists of polygons that are not regions. Note that {{is_region_simple()}} will identify
// regions with no polygon intersections at all, which should render successfully witih CGAL.
// .
// The actual geometry of the region is defined by XORing together
// all of the polygons on the list. This may sound obscure, but it simply means that nested
// all of the polygons in the list. This may sound obscure, but it simply means that nested
// boundaries make rings in the obvious fashion, and non-nested shapes simply union together.
// Checking that a list of paths is a valid region, meaning that it satisfies all of the conditions
// Checking that a list of polygons is a valid region, meaning that it satisfies all of the conditions
// above, can be a time consuming test, so it is not done automatically. It is your responsibility to ensure that your regions are
// compliant. You can construct regions by making a list of polygons, or by using
// boolean function operations such as union() or difference(), which all acccept paths, as
// compliant. You can construct regions by making a suitable list of polygons, or by using
// set operation function such as union() or difference(), which all acccept polygons, as
// well as regions, as their inputs. And if you must you can clean up an ill-formed region using make_region(),
// which will break up self-intersecting paths and paths that cross each other.
// which will break up self-intersecting polygons and polygons that cross each other.
// Function: is_region()
// Usage:
// is_region(x);
// Description:
// Returns true if the given item looks like a region. A region is a list of non-crossing simple paths. This test just checks
// Returns true if the given item looks like a region. A region is a list of non-crossing simple polygons. This test just checks
// that the argument is a list whose first entry is a path.
function is_region(x) = is_list(x) && is_path(x.x);
@ -48,16 +52,16 @@ function is_region(x) = is_list(x) && is_path(x.x);
// Usage:
// bool = is_valid_region(region, [eps]);
// Description:
// Returns true if the input is a valid region, meaning that it is a list of simple paths whose segments do not cross each other.
// Returns true if the input is a valid region, meaning that it is a list of simple polygons whose segments do not cross each other.
// This test can be time consuming with regions that contain many points.
// It differs from `is_region()` which simply checks that the object appears to be a list of paths
// because it searches all the region paths for any self-intersections or intersections with each other.
// Will also return true if given a single simple path. Use {{make_region()}} to convert sets of self-intersecting polygons into
// It differs from `is_region()` which simply checks that the object is a list whose first entry is a path
// because it searches all the list polygons for any self-intersections or intersections with each other.
// Will also return true if given a single simple polygon. Use {{make_region()}} to convert sets of self-intersecting polygons into
// a region.
// Arguments:
// region = region to check
// eps = tolerance for geometric comparisons. Default: `EPSILON` = 1e-9
// Example(2D,NoAxes): In all of the examples each path in the region appears in a different color. Two non-intersecting squares make a valid region.
// Example(2D,NoAxes): In all of the examples each polygon in the region appears in a different color. Two non-intersecting squares make a valid region.
// region = [square(10), right(11,square(8))];
// rainbow(region)stroke($item, width=.2,closed=true);
// back(11)text(is_valid_region(region) ? "region" : "non-region", size=2);
@ -73,23 +77,27 @@ function is_region(x) = is_list(x) && is_path(x.x);
// object = [square(10), move([8,8], square(8))];
// rainbow(object)stroke($item, width=.2,closed=true);
// back(17)text(is_valid_region(object) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): Not a region due to a self-intersecting (non-simple) hourglass path
// Example(2D,NoAxes): A union is one way to fix the above example and get a region. (Note that union is run here on two simple polygons, which are valid regions themselves and hence acceptable inputs to union.
// region = union([square(10), move([8,8], square(8))]);
// rainbow(region)stroke($item, width=.25,closed=true);
// back(12)text(is_valid_region(region) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): Not a region due to a self-intersecting (non-simple) hourglass polygon
// object = [move([-2,-2],square(14)), [[0,0],[10,0],[0,10],[10,10]]];
// rainbow(object)stroke($item, width=.2,closed=true);
// move([-1.5,13])text(is_valid_region(object) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): Breaking hourglass in half fixes it. Now it's a region:
// region = [move([-2,-2],square(14)), [[0,0],[10,0],[5,5]], [[5,5],[0,10],[10,10]]];
// rainbow(region)stroke($item, width=.2,closed=true);
// Example(2D,NoAxes): A single path corner touches an edge, so not a region:
// Example(2D,NoAxes): A single polygon corner touches an edge, so not a region:
// object = [[[-10,0], [-10,10], [20,10], [20,-20], [-10,-20],
// [-10,-10], [0,0], [10,-10], [10,0]]];
// rainbow(object)stroke($item, width=.3,closed=true);
// move([-4,12])text(is_valid_region(object) ? "region" : "non-region", size=3);
// Example(2D,NoAxes): Corners touch in the same path, so the path is not simple and the object is not a region.
// Example(2D,NoAxes): Corners touch in the same polygon, so the polygon is not simple and the object is not a region.
// object = [[[0,0],[10,0],[10,10],[-10,10],[-10,0],[0,0],[-5,5],[5,5]]];
// rainbow(object)stroke($item, width=.3,closed=true);
// move([-10,12])text(is_valid_region(object) ? "region" : "non-region", size=3);
// Example(2D,NoAxes): The shape above as a valid region with two paths:
// Example(2D,NoAxes): The shape above as a valid region with two polygons:
// region = [ [[0,0],[10,0],[10,10],[-10,10],[-10,0]],
// [[0,0],[5,5],[-5,5]] ];
// rainbow(region)stroke($item, width=.3,closed=true);
@ -98,10 +106,6 @@ function is_region(x) = is_list(x) && is_path(x.x);
// region = [square(10), move([10,10], square(8))];
// rainbow(region)stroke($item, width=.25,closed=true);
// back(12)text(is_valid_region(region) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): A union is one way to fix the above example and get a region. (Note that union is run here on two simple paths, which are valid regions themselves and hence acceptable inputs to union.
// region = union([square(10), move([8,8], square(8))]);
// rainbow(region)stroke($item, width=.25,closed=true);
// back(12)text(is_valid_region(region) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): These two squares share part of an edge, hence not a region
// object = [square(10), move([10,2], square(7))];
// stroke(object[0], width=0.2,closed=true);
@ -121,11 +125,11 @@ function is_region(x) = is_list(x) && is_path(x.x);
// object = [square(10), [[10,0],[0,10],[8,13],[13,8]]];
// rainbow(object)stroke($item, width=.2,closed=true);
// back(14)text(is_valid_region(object) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): One path touches another in the middle of an edge
// Example(2D,NoAxes): One polygon touches another in the middle of an edge
// object = [square(10), [[10,5],[15,0],[15,10]]];
// rainbow(object)stroke($item, width=.2,closed=true);
// back(11)text(is_valid_region(object) ? "region" : "non-region", size=2);
// Example(2D,NoAxes): The path touches the side, but the side has a vertex at the contact point so this is a region
// Example(2D,NoAxes): The polygon touches the side, but the side has a vertex at the contact point so this is a region
// poly1 = [ each square(30,center=true), [15,0]];
// poly2 = right(10,circle(5,$fn=4));
// poly3 = left(0,circle(5,$fn=4));
@ -134,7 +138,7 @@ function is_region(x) = is_list(x) && is_path(x.x);
// rainbow(region)stroke($item, width=.25,closed=true);
// move([-5,16.5])text(is_valid_region(region) ? "region" : "non-region", size=3);
// color("black")move_copies(region[0]) circle(r=.4);
// Example(2D,NoAxes): The path touches the side, but not at a vertex so this is not a region
// Example(2D,NoAxes): The polygon touches the side, but not at a vertex so this is not a region
// poly1 = fwd(4,[ each square(30,center=true), [15,0]]);
// poly2 = right(10,circle(5,$fn=4));
// poly3 = left(0,circle(5,$fn=4));
@ -143,13 +147,13 @@ function is_region(x) = is_list(x) && is_path(x.x);
// rainbow(object)stroke($item, width=.25,closed=true);
// move([-9,12.5])text(is_valid_region(object) ? "region" : "non-region", size=3);
// color("black")move_copies(object[0]) circle(r=.4);
// Example(2D,NoAxes): The inner path touches the middle of the edges, so not a region
// Example(2D,NoAxes): The inner polygon touches the middle of the edges, so not a region
// poly1 = square(20,center=true);
// poly2 = circle(10,$fn=8);
// object=[poly1,poly2];
// rainbow(object)stroke($item, width=.25,closed=true);
// move([-10,11.4])text(is_valid_region(object) ? "region" : "non-region", size=3);
// Example(2D,NoAxes): The above shape made into a region using difference():
// Example(2D,NoAxes): The above shape made into a region using {{difference()}} now has four components that touch at corners
// poly1 = square(20,center=true);
// poly2 = circle(10,$fn=8);
// region = difference(poly1,poly2);
@ -212,7 +216,15 @@ function _polygon_crosses_region(region, poly, eps=EPSILON) =
// Arguments:
// region = region to check
// eps = tolerance for geometric comparisons. Default: `EPSILON` = 1e-9
function is_simple_region(region, eps=EPSILON) =
// Example(2D,NoAxes): Corner contact means it's not simple
// region = [move([-2,-2],square(14)), [[0,0],[10,0],[5,5]], [[5,5],[0,10],[10,10]]];
// rainbow(region)stroke($item, width=.2,closed=true);
// move([-1,13])text(is_region_simple(region) ? "simple" : "not-simple", size=2);
// Example(2D,NoAxes): Moving apart the triangles makes it simple:
// region = [move([-2,-2],square(14)), [[0,0],[10,0],[5,4.5]], [[5,5.5],[0,10],[10,10]]];
// rainbow(region)stroke($item, width=.2,closed=true);
// move([1,13])text(is_region_simple(region) ? "simple" : "not-simple", size=2);
function is_region_simple(region, eps=EPSILON) =
let(region=force_region(region))
assert(is_region(region), "Input is not a region")
[for(p=region) if (!is_path_simple(p,closed=true,eps=eps)) 1] == []
@ -224,32 +236,41 @@ function is_simple_region(region, eps=EPSILON) =
// Function: make_region()
// Usage:
// r_fixed = make_region(r, [nonzero], [eps]);
// region = make_region(polys, [nonzero], [eps]);
// Description:
// Takes a malformed input region that contains self-intersecting polygons or polygons
// that cross each other and converts it into a properly defined region without
// Takes a list of polygons that may intersect themselves or cross each other
// and converts it into a properly defined region without
// these defects.
// Arguments:
// r = region to sanitize
// polys = list of polygons to use
// nonzero = set to true to use nonzero rule for polygon membership. Default: false
// eps = Epsilon for geometric comparisons. Default: `EPSILON` (1e-9)
// Examples:
//
function make_region(r,nonzero=false,eps=EPSILON) =
let(r=force_region(r))
assert(is_region(r), "Input is not a region")
// Example(2D,NoAxes): The pentagram is self-intersecting, so it is not a region. Here it becomes five triangles:
// pentagram = turtle(["move",100,"left",144], repeat=4);
// region = make_region(pentagram);
// rainbow(region)stroke($item, width=1,closed=true);
// Examples(2D,NoAxes): Alternatively with the nonzero option you can get the perimeter:
// pentagram = turtle(["move",100,"left",144], repeat=4);
// region = make_region(pentagram,nonzero=true);
// stroke(region, width=1,closed=true);
// Example(2D,NoAxes): To crossing squares become two L-shaped components
// region = make_region([square(10), move([5,5],square(8))]);
// rainbow(region)stroke($item, width=.3,closed=true);
function make_region(polys,nonzero=false,eps=EPSILON) =
let(polys=force_region(polys))
assert(is_region(polys), "Input is not a region")
exclusive_or(
[for(poly=r) each polygon_parts(poly,nonzero,eps)],
[for(poly=polys) each polygon_parts(poly,nonzero,eps)],
eps=eps);
// Function: force_region()
// Usage:
// region = force_region(path)
// region = force_region(poly)
// Description:
// If the input is a path then return it as a region. Otherwise return it unaltered.
function force_region(path) = is_path(path) ? [path] : path;
// If the input is a polygon then return it as a region. Otherwise return it unaltered.
// Arguments:
// poly = polygon to turn into a region
function force_region(poly) = is_path(poly) ? [poly] : poly;
// Section: Turning a region into geometry
@ -258,12 +279,14 @@ function force_region(path) = is_path(path) ? [path] : path;
// Usage:
// region(r);
// Description:
// Creates 2D polygons for the given region. The region given is a list of closed 2D paths.
// Each path will be effectively exclusive-ORed from all other paths in the region, so if a
// path is inside another path, it will be effectively subtracted from it.
// Example(2D):
// 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
// Example(2D): Displaying a region
// region([circle(d=50), square(25,center=true)]);
// Example(2D):
// Example(2D): Displaying a list of polygons that intersect each other, which is not a region
// rgn = concat(
// [for (d=[50:-10:10]) circle(d=d-5)],
// [square([60,10], center=true)]
@ -283,27 +306,36 @@ module region(r)
// Section: Gometrical calculations with region
// Section: Gometrical calculations with regions
// Function: point_in_region()
// Usage:
// check = point_in_region(point, region, [eps]);
// Description:
// Tests if a point is inside, outside, or on the border of a region.
// Tests if a point is inside, outside, or on the border of a region.
// Returns -1 if the point is outside the region.
// Returns 0 if the point is on the boundary.
// Returns 1 if the point lies inside the region.
// Arguments:
// point = The point to test.
// region = The region to test against. Given as a list of polygon paths.
// region = The region to test against, as a list of polygon paths.
// eps = Acceptable variance. Default: `EPSILON` (1e-9)
function point_in_region(point, region, eps=EPSILON, _i=0, _cnt=0) =
_i >= len(region) ? ((_cnt%2==1)? 1 : -1)
: let(
pip = point_in_polygon(point, region[_i], eps=eps)
)
pip==0? 0
: point_in_region(point, region, eps=eps, _i=_i+1, _cnt = _cnt + (pip>0? 1 : 0));
// Example(2D,NoAxes):
// region = [for(i=[2:8]) hexagon(r=i)];
// for(x=[-4:4],y=[-4:4]) color(point_in_region
function point_in_region(point, region, eps=EPSILON) =
let(region=force_region(region))
assert(is_region(region), "Region given to point_in_region is not a region")
assert(is_vector(point,2), "Point must be a 2D point in point_in_region")
_point_in_region(point, region, eps);
function pointin_region(point, region, eps=EPSILON, i=0, cnt=0) =
i >= len(region) ? ((cnt%2==1)? 1 : -1)
: let(
pip = point_in_polygon(point, region[i], eps=eps)
)
pip == 0 ? 0
: _point_in_region(point, region, eps=eps, i=i+1, cnt = cnt + (pip>0? 1 : 0));
// Function: region_area()
@ -312,6 +344,10 @@ function point_in_region(point, region, eps=EPSILON, _i=0, _cnt=0) =
// Description:
// Computes the area of the specified valid region. (If the region is invalid and has self intersections
// the result is meaningless.)
// Arguments:
// region = region whose area to compute
// Examples:
// area = region_area([square(10), right(20,square(8))]); // Returns 164
function region_area(region) =
assert(is_region(region), "Input must be a region")
let(
@ -437,9 +473,13 @@ function _region_region_intersections(region1, region2, closed1=true,closed2=tru
// Splits region1 at the places where polygons in region1 touches each other at corners and at locations
// where region1 intersections region2. Split region2 similarly with respect to region1.
// The return is a pair of results of the form [split1, split2] where split1=[frags1,frags2,...]
// and frags1 is a list of path pieces (in order) from the first path of the region.
// You can pass a single path in for either region, but the output will be a singleton list, as ify
// you passed in a singleton region.
// and frags1 is a list of paths that when placed end to end (in the given order), give the first polygon of region1.
// Each path in the list is either entirely inside or entirely outside region2.
// Then frags2 is the decomposition of the second polygon into path pieces, and so on. Finally split2 is
// the same list, but for the polygons in region2.
// You can pass a single polygon in for either region, but the output will be a singleton list, as if
// you passed in a singleton region. If you set the closed parameters to false then the region components
// will be treated as open paths instead of polygons.
// Arguments:
// region1 = first region
// region2 = second region
@ -543,9 +583,9 @@ function region_parts(region) =
// Usage:
// linear_sweep(region, height, [center], [slices], [twist], [scale], [style], [convexity]);
// Description:
// If called as a module, creates a polyhedron that is the linear extrusion of the given 2D region or path.
// 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
// of the given 2D region or path. The benefit of using this, over using `linear_extrude region(rgn)` is
// of the given 2D region or polygon. The benefit of using this, over using `linear_extrude region(rgn)` is
// that it supports `anchor`, `spin`, `orient` and attachments. You can also make more refined
// twisted extrusions by using `maxseg` to subsample flat faces.
// Note that the center option centers vertically using the named anchor "zcenter" whereas
@ -553,7 +593,7 @@ function region_parts(region) =
// the shape's centroid, or other centerpoint you specify. The centerpoint can be "centroid", "mean", "box" or
// a custom point location.
// Arguments:
// region = The 2D [Region](regions.scad) or path that is to be extruded.
// region = The 2D [Region](regions.scad) or polygon that is to be extruded.
// height = The height to extrude the region. Default: 1
// center = If true, the created polyhedron will be vertically centered. If false, it will be extruded upwards from the XY plane. Default: `false`
// slices = The number of slices to divide the shape into along the Z axis, to allow refinement of detail, especially when working with a twist. Default: `twist/5`
@ -656,7 +696,7 @@ function linear_sweep(region, height=1, center, twist=0, scale=1, slices,
// Section: Offsets and Boolean 2D Geometry
// Section: Offset and 2D Boolean Set Operations
function _offset_chamfer(center, points, delta) =
@ -773,10 +813,11 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// offsetpath = offset(path, [r|delta], [chamfer], [closed], [check_valid], [quality])
// path_faces = offset(path, return_faces=true, [r|delta], [chamfer], [closed], [check_valid], [quality], [firstface_index], [flip_faces])
// Description:
// Takes a 2D input path and returns a path offset by the specified amount. As with the built-in
// Takes a 2D input path, polygon or region and returns a path offset by the specified amount. As with the built-in
// offset() module, you can use `r` to specify rounded offset and `delta` to specify offset with
// corners. If you used `delta` you can set `chamfer` to true to get chamfers.
// Positive offsets shift the path to the left (relative to the direction of the path). Note
// For paths and polygons positive offsets make the polygons larger. For paths,
// positive offsets shift the path to the left, relative to the direction of the path. Note
// that the path must not include any 180 degree turns, where the path reverses direction.
// .
// When offsets shrink the path, segments cross and become invalid. By default `offset()` checks
@ -800,7 +841,7 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// r = offset radius. Distance to offset. Will round over corners.
// delta = offset distance. Distance to offset with pointed corners.
// chamfer = chamfer corners when you specify `delta`. Default: false
// closed = path is a closed curve. Default: False.
// closed = if true path is treate as a polygon. Default: False.
// check_valid = perform segment validity check. Default: True.
// quality = validity check quality parameter, a small integer. Default: 1.
// return_faces = return face list. Default: False.
@ -1050,11 +1091,11 @@ function _list_three(a,b,c) =
// region = union(REGION1,REGION2);
// region = union(REGION1,REGION2,REGION3);
// Description:
// When called as a function and given a list of regions, where each region is a list of closed
// 2D paths, returns the boolean union of all given regions. Result is a single region.
// When called as the built-in module, makes the boolean union of the given children.
// When called as a function and given a list of regions or 2D polygons,
// returns the union of all given regions and polygons. Result is a single region.
// When called as the built-in module, makes the union of the given children.
// Arguments:
// regions = List of regions to union. Each region is a list of closed paths.
// regions = List of regions to union.
// Example(2D):
// shape1 = move([-8,-8,0], p=circle(d=50));
// shape2 = move([ 8, 8,0], p=circle(d=50));
@ -1080,12 +1121,12 @@ function union(regions=[],b=undef,c=undef,eps=EPSILON) =
// region = difference(REGION1,REGION2);
// region = difference(REGION1,REGION2,REGION3);
// Description:
// When called as a function, and given a list of regions, where each region is a list of closed
// 2D paths, takes the first region and differences away all other regions from it. The resulting
// When called as a function, and given a list of regions or 2D polygons,
// takes the first region or polygon and differences away all other regions/polygons from it. The resulting
// region is returned.
// When called as the built-in module, makes the boolean difference of the given children.
// When called as the built-in module, makes the set difference of the given children.
// Arguments:
// regions = List of regions to difference. Each region is a list of closed paths.
// regions = List of regions or polygons to difference.
// Example(2D):
// shape1 = move([-8,-8,0], p=circle(d=50));
// shape2 = move([ 8, 8,0], p=circle(d=50));
@ -1112,11 +1153,11 @@ function difference(regions=[],b=undef,c=undef,eps=EPSILON) =
// region = intersection(REGION1,REGION2);
// region = intersection(REGION1,REGION2,REGION3);
// Description:
// When called as a function, and given a list of regions, where each region is a list of closed
// 2D paths, returns the boolean intersection of all given regions. Result is a single region.
// When called as the built-in module, makes the boolean intersection of all the given children.
// When called as a function, and given a list of regions or polygons returns the
// intersection of all given regions. Result is a single region.
// When called as the built-in module, makes the intersection of all the given children.
// Arguments:
// regions = List of regions to intersection. Each region is a list of closed paths.
// regions = List of regions to intersect.
// Example(2D):
// shape1 = move([-8,-8,0], p=circle(d=50));
// shape2 = move([ 8, 8,0], p=circle(d=50));
@ -1143,12 +1184,13 @@ function intersection(regions=[],b=undef,c=undef,eps=EPSILON) =
// region = exclusive_or(REGION1,REGION2);
// region = exclusive_or(REGION1,REGION2,REGION3);
// Description:
// When called as a function and given a list of regions, where each region is a list of closed
// 2D paths, returns the boolean exclusive_or of all given regions. Result is a single region.
// When called as a module, performs a boolean exclusive-or of up to 10 children. Note that the
// xor operator tends to produce shapes that meet at corners, which do not render in CGAL.
// When called as a function and given a list of regions or 2D polygons,
// returns the exclusive_or of all given regions. Result is a single region.
// When called as a module, performs a boolean exclusive-or of up to 10 children. Note that when
// the input regions cross each other the exclusive-or operator will produce shapes that
// meet at corners (non-simple regions), which do not render in CGAL.
// Arguments:
// regions = List of regions to exclusive_or. Each region is a list of closed paths.
// regions = List of regions or polygons to exclusive_or
// Example(2D): As Function. A linear_sweep of this shape fails to render in CGAL.
// shape1 = move([-8,-8,0], p=circle(d=50));
// shape2 = move([ 8, 8,0], p=circle(d=50));