BOSL2/skin.scad

//////////////////////////////////////////////////////////////////////
// LibFile: skin.scad
//   Functions to skin arbitrary 2D profiles/paths in 3-space.
//   To use, add the following line to the beginning of your file:
//   ```
//   include <BOSL2/std.scad>
//   include <BOSL2/skin.scad>
//   ```
//   Derived from list-comprehension-demos skin():
//   - https://github.com/openscad/list-comprehension-demos/blob/master/skin.scad
//////////////////////////////////////////////////////////////////////


include <vnf.scad>


// Section: Skinning


// Function&Module: skin()
// Usage: As Module
//   skin(profiles, [closed], [matching]);
// Usage: As Function
//   vnf = skin(profiles, [closed], [caps], [matching]);
// Description
//   Given a list of two or more 2D path `profiles` that have been moved and/or rotated into 3D-space,
//   produces faces to skin a surface between consecutive profiles.  Optionally, the first and last
//   profiles can have endcaps, or the last and first profiles can be skinned together.
//   The user is responsible for making sure the orientation of the first vertex of each profile are relatively aligned.
//   If called as a function, returns a VNF structure like `[VERTICES, FACES]`.  See [VNF](vnf.scad).
//   If called as a module, creates a polyhedron of the skinned profiles.
//   The vertex matching algorithms are as follows:
//   - `"distance"`: Vertices between profiles are matched based on closest next position, relative to the center of each profile.
//   - `"angle"`: Vertices between profiles are matched based on closest next polar angle, relative to the center of each profile.
//   - `"evenly"`: Vertices are evenly matched between profiles, such that a point 30% of the way through one profile, will be matched to a vertex 30% of the way through the other profile, based on vertex count.
// Arguments:
//   profiles = A list of 2D paths that have been moved and/or rotated into 3D-space.
//   closed = If true, the last profile is skinned to the first profile, to allow for making a closed loop.  Assumes `caps=false`.  Default: false
//   caps = If true, endcap faces are created.  Assumes `closed=false`.  Default: true
//   matching = Specifies the algorithm used to match up vertices between profiles, to create faces.  Given as a string, one of `"distance"`, `"angle"`, or `"evenly"`.  If given as a list of strings, equal in number to the number of profile transitions, lets you specify the algorithm used for each transition.  Default: "distance"
// Example(FlatSpin):
//   skin([
//       move([0,0,  0], p=scale([2,1,1], p=path3d(circle(d=100,$fn=48)))),
//       move([0,0,100], p=path3d(circle(d=100,$fn=4))),
//       move([0,0,200], p=path3d(circle(d=100,$fn=12))),
//   ]);
// Example(FlatSpin):
//   skin([
//       for (ang = [0:10:90])
//       rot([0,ang,0], cp=[200,0,0], p=path3d(circle(d=100,$fn=3+(ang/10))))
//   ]);
// Example(FlatSpin): Möbius Strip
//   skin([
//       for (ang = [0:10:360])
//       rot([0,ang,0], cp=[100,0,0], p=rot(ang/2, p=path3d(square([1,30],center=true))))
//   ], caps=false);
// Example(FlatSpin): Closed Loop
//   skin([
//       for (i = [0:5])
//       rot([0,i*60,0], cp=[100,0,0], p=path3d(circle(d=30,$fn=3+i%3)))
//   ], closed=true, caps=false);
// Example: Distance Matching
//   skin([
//       move([0,0,  0], p=scale([1,2,1],p=path3d(circle(d=50,$fn=36)))),
//       move([0,0,100], p=scale([2,1,1],p=path3d(circle(d=50,$fn=36))))
//   ], matching="distance");
// Example: Angle Matching
//   skin([
//       move([0,0,  0], p=scale([1,2,1],p=path3d(circle(d=50,$fn=36)))),
//       move([0,0,100], p=scale([2,1,1],p=path3d(circle(d=50,$fn=36))))
//   ], matching="angle");
// Example: Evenly Matching
//   skin([
//       move([0,0,  0], p=scale([1,2,1],p=path3d(circle(d=50,$fn=36)))),
//       move([0,0,100], p=scale([2,1,1],p=path3d(circle(d=50,$fn=36))))
//   ], matching="evenly");
// Example: Beware Self-intersecting Creases!
//   skin([
//       for (a = [0:30:180]) let(
//           pos  = [-60*sin(a),     0, a    ],
//           pos2 = [-60*sin(a+0.1), 0, a+0.1]
//       ) move(pos,
//           p=rot(from=UP, to=pos2-pos,
//               p=path3d(circle(d=150))
//           )
//       )
//   ]);
//   color("red") {
//       zrot(25) fwd(130) xrot(75) {
//           linear_extrude(height=0.1) {
//               ydistribute(25) {
//                   text(text="BAD POLYHEDRONS!", size=20, halign="center", valign="center");
//                   text(text="CREASES MAKE", size=20, halign="center", valign="center");
//               }
//           }
//       }
//       up(160) zrot(25) fwd(130) xrot(75) {
//           stroke(zrot(30, p=yscale(0.5, p=circle(d=120))),width=10,closed=true);
//       }
//   }
// Example: Beware Making Incomplete Polyhedrons!
//   skin([
//       move([0,0, 0], p=path3d(circle(d=100,$fn=36))),
//       move([0,0,50], p=path3d(circle(d=100,$fn=6)))
//   ], caps=false);
module skin(profiles, closed=false, caps=true, matching="distance") {
	vnf_polyhedron(skin(profiles, caps=caps, closed=closed, matching=matching));
}


function skin(profiles, closed=false, caps=true, matching="distance") =
	assert(is_list(profiles))
	assert(is_bool(closed))
	assert(is_bool(caps))
	assert(!closed||!caps)
	assert(is_string(matching)||is_list(matching))
	let( matching = is_list(matching)? matching : [for (pidx=idx(profiles,end=closed?-1:-2)) matching] )
	assert(len(matching) == len(profiles)-closed?0:1)
	vnf_triangulate(
		concat([
			for(pidx=idx(profiles,end=closed? -1 : -2))
			let(
				prof1 = profiles[pidx%len(profiles)],
				prof2 = profiles[(pidx+1)%len(profiles)],
				cp1 = mean(prof1),
				cp2 = mean(prof2),
				midpt = (cp1+cp2)/2,
				n1 = plane_normal(plane_from_pointslist(prof1)),
				n2 = plane_normal(plane_from_pointslist(prof2)),
				vang = vector_angle(n1,n2),
				perp = vang>0.01 && vang<179.99? vector_axis(n1,n2) :
					vector_angle(n1,UP)>44? vector_axis(n1,UP) :
					vector_axis(n1,LEFT),
				perp1 = vector_axis(n1,perp),
				perp2 = vector_axis(n2,perp),
				poly1 = ccw_polygon(project_plane(prof1, cp1, cp1+perp, cp1+perp1)),
				poly2 = ccw_polygon(project_plane(prof2, cp2, cp2+perp, cp2+perp2)),
				match = matching[pidx],
				faces = [
					for(
						first = true,
						finishing = false,
						finished = false,
						plen1 = len(poly1),
						plen2 = len(poly2),
						i=0, j=0, side=0;

						!finished;

						dang1 = abs(xy_to_polar(poly1[i%plen1]).y - xy_to_polar(poly2[(j+1)%plen2]).y),
						dang2 = abs(xy_to_polar(poly2[j%plen2]).y - xy_to_polar(poly1[(i+1)%plen1]).y),
						dist1 = norm(poly1[i%plen1] - poly2[(j+1)%plen2]),
						dist2 = norm(poly2[j%plen2] - poly1[(i+1)%plen1]),
						side = i>=plen1? 0 :
							j>=plen2? 1 :
							match=="angle"? (dang1>dang2? 1 : 0) :
							match=="distance"? (dist1>dist2? 1 : 0) :
							match=="evenly"? (i/plen1 > j/plen2? 0 : 1) :
							assert(in_list(matching[i],["angle","distance","evenly"]),str("Got `",matching,"'")),
						p1 = lift_plane(poly1[i%plen1], cp1, cp1+perp, cp1+perp1),
						p2 = lift_plane(poly2[j%plen2], cp2, cp2+perp, cp2+perp2),
						p3 = side?
							lift_plane(poly1[(i+1)%plen1], cp1, cp1+perp, cp1+perp1) :
							lift_plane(poly2[(j+1)%plen2], cp2, cp2+perp, cp2+perp2),
						face = [p1, p3, p2],
						i = i + (side? 1 : 0),
						j = j + (side? 0 : 1),
						first = false,
						finished = finishing,
						finishing = i>=plen1 && j>=plen2
					) if (!first) face
				]
			) vnf_add_faces(faces=faces)
		], closed||!caps? [] : let(
			prof1 = profiles[0],
			prof2 = select(profiles,-1),
			ncl1 = sort(find_noncollinear_points(prof1)),
			ncl2 = sort(find_noncollinear_points(prof2)),
			pa1=prof1[ncl1.x], pa2=prof1[ncl1.y], pa3=prof1[ncl1.z],
			pb1=prof2[ncl2.x], pb2=prof2[ncl2.y], pb3=prof2[ncl2.z],
			poly1 = ccw_polygon(project_plane(prof1, pa1, pa2, pa3)),
			poly2 = clockwise_polygon(project_plane(prof2, pb1, pb2, pb3))
		) [
			vnf_add_face(pts=lift_plane(poly1, pa1, pa2, pa3)),
			vnf_add_face(pts=lift_plane(poly2, pb1, pb2, pb3))
		])
	);


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