Twist: closed beginning & end properly.

Yes, it checks out as a manifold mesh too.

src/examples.rs

@@ -303,12 +303,13 @@ impl Twist {
 
     pub fn init() -> (Twist, Rule<Twist>) {
         let subdiv = 2;
+        let xf = geometry::Rotation3::from_axis_angle(&Vector3::x_axis(), -0.7).to_homogeneous();
         let seed = vec![
             vertex(-0.5,  0.0, -0.5),
             vertex( 0.5,  0.0, -0.5),
             vertex( 0.5,  0.0,  0.5),
             vertex(-0.5,  0.0,  0.5),
-        ];
+        ].iter().map(|v| xf * v).collect();
         let seed_sub = util::subdivide_cycle(&seed, subdiv);
         let t = Twist {
             dx0: 2.0,
@@ -342,23 +343,23 @@ impl Twist {
             Child {
                 rule: Rule { eval: Self::recur },
                 xf: xf,
-                vmap: (n*i..n*(i+self.count)).collect(), // N.B.
+                vmap: ((n+1)*i..(n+1)*(i+self.count)).collect(), // N.B.
+                // note n+1, not n. the +1 is for the centroid below
             }
         }).collect();
 
         // Use byproducts of this to make 'count' copies of 'seed' with
         // this same transform:
-        let mut verts = vec![];
-        for child in &children {
-            verts.extend(self.seed_sub.iter().map(|v| child.xf * v));
-        }
+        let meshes = children.iter().map(|child| {
+            let mut vs = self.seed_sub.iter().map(|v| child.xf * v).collect();
+            // and in the process, generate faces for these seeds:
+            let (centroid, f) = util::connect_convex(&vs, false);
+            vs.push(centroid);
+            OpenMesh { verts: vs, faces: f }
+        });
         
         RuleEval {
-            geom: OpenMesh {
-                verts: verts,
-                faces: vec![],
-                // TODO: Close these initial faces off
-            },
+            geom: OpenMesh::append(meshes),
             final_geom: prim::empty_mesh(),
             children: children,
         }
@@ -374,12 +375,14 @@ impl Twist {
         let seed_sub = util::subdivide_cycle(&seed_orig, self.subdiv);
         let n = seed_sub.len();
 
+        let (vc, faces) = util::connect_convex(&seed_sub, true);
+        
         RuleEval {
             geom: OpenMesh {
                 verts: seed_sub,
                 faces: util::parallel_zigzag_faces(n),
             },
-            final_geom: prim::empty_mesh(), // TODO: Close properly
+            final_geom: OpenMesh { verts: vec![vc], faces },
             children: vec![
                 Child {
                     rule: Rule { eval: Self::recur },
@@ -439,5 +442,5 @@ pub fn main() {
     // TODO: If I increase the above from 100 to ~150, Blender reports
     // that the very tips are non-manifold.  I am wondering if this is
     // some sort of numerical precision issue.
-    run_test_iter(Twist::init(), 200, "twist2");
+    run_test_iter(Twist::init(), 100, "twist2");
 }

src/openmesh.rs

@@ -39,6 +39,31 @@ pub struct OpenMesh {
 
 impl OpenMesh {
 
+    pub fn append<T>(meshes: T) -> OpenMesh
+    where T: IntoIterator<Item = OpenMesh>
+    {
+        let mut v: Vec<Vertex> = vec![];
+        let mut f: Vec<Tag> = vec![];
+        for mesh in meshes {
+            // Position in 'verts' at which we're appending
+            // mesh.verts, which we need to know to shift indices:
+            let offset = v.len();
+            
+            // Copy all vertices:
+            v.append(&mut mesh.verts.clone());
+            // Append its faces, applying offset:
+            f.extend(mesh.faces.iter().map(|t| {
+                match t {
+                    Tag::Body(n) => Tag::Body(n + offset),
+                    Tag::Parent(_) => panic!("Cannot append() if mesh has parent references!"),
+                    // TODO: Handle the above
+                }
+            }));
+        }
+           
+        OpenMesh { verts: v, faces: f }
+    }
+    
     /// Returns a new `OpenMesh` whose vertices have been transformed.
     pub fn transform(&self, xfm: &Mat4) -> OpenMesh {
         OpenMesh {

src/rule.rs

@@ -151,6 +151,12 @@ impl<A> Rule<A> {
             let s = &mut stack[n-1];
             let depth = s.depth;
 
+            if s.rules.is_empty() {
+                stack.pop();
+                n -= 1;
+                continue;
+            }
+            
             // Evaluate the rule:
             let child = &s.rules[s.next];
             let mut eval = (child.rule.eval)(arg);

src/util.rs

@@ -29,3 +29,29 @@ pub fn parallel_zigzag_faces(count: usize) -> Vec<Tag> {
         ]
     }).flatten().collect()
 }
+
+pub fn connect_convex(verts: &Vec<Vertex>, as_parent: bool) -> (Vertex, Vec<Tag>) {
+    let n = verts.len();
+    let mut centroid = Vertex::new(0.0, 0.0, 0.0, 0.0);
+    for v in verts {
+        centroid += v;
+    }
+    centroid /= n as f32;
+
+    let faces: Vec<Tag> = {
+        if as_parent {
+            (0..n).map(|f1| {
+                let f2 = (f1 + 1) % n;
+                vec![Tag::Parent(f2), Tag::Parent(f1), Tag::Body(0)]
+            }).flatten().collect()
+        } else {
+            (0..n).map(|f1| {
+                let f2 = (f1 + 1) % n;
+                // n is used for new center vertex
+                vec![Tag::Body(f1), Tag::Body(f2), Tag::Body(n)]
+            }).flatten().collect()
+        }
+    };
+
+    (centroid, faces)
+}