Added some helpers in util.rs

README.md

@@ -2,7 +2,7 @@
 
 ## Highest priority:
 
-- Fix `twist` example.
+- Clean up `twist` - maybe make a struct or trait.
 - Do transforms compose in the *reverse* of automata_scratch? This
   appears to be the case.
 

src/examples.rs

@@ -4,6 +4,7 @@ use nalgebra::*;
 use crate::openmesh::{OpenMesh, Tag, Mat4, Vertex, vertex};
 use crate::rule::{Rule, RuleStep, Child};
 use crate::prim;
+use crate::util;
 
 fn curve_horn_start() -> RuleStep {
     let id = nalgebra::geometry::Transform3::identity().to_homogeneous();
@@ -267,19 +268,19 @@ fn ram_horn_branch() -> RuleStep {
 // Meant to be a copy of twist_from_gen from Python & automata_scratch
 pub fn twist_start() -> RuleStep {
     //let ang=0.1;
-    let dz=0.2;
     let dx0=2.0;
-    let dy=0.1;
     let count=4;
     // TODO: Factor these out (see twist)
 
-    let seed = vec![
+    let seed = util::subdivide_cycle(&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),
-        vertex( 0.5,  0.0, -0.5),        
-    ];
-    // TODO: Subdivide method
+        vertex(-0.5,  0.0,  0.5),
+    ], 2);
+    // TODO: Factor out
+    let n = seed.len();
+    // TODO: Factor out subdiv size
     
     // Quarter-turn in radians:
     let qtr = std::f32::consts::FRAC_PI_2;
@@ -296,7 +297,7 @@ pub fn twist_start() -> RuleStep {
         Child {
             rule: Rule::Recurse(twist),
             xf: xf,
-            vmap: (4*i..4*(i+count)).collect(), // N.B.
+            vmap: (n*i..n*(i+count)).collect(), // N.B.
         }
     }).collect();
 
@@ -320,10 +321,8 @@ pub fn twist_start() -> RuleStep {
 
 pub fn twist() -> RuleStep {
     let ang=0.1;
-    let dz=0.2;
     let dx0=2.0;
     let dy=0.1;
-    let count=4;
     // TODO: Factor these out (see twist_start)
 
     let y = &Vector3::y_axis();
@@ -331,34 +330,28 @@ pub fn twist() -> RuleStep {
         geometry::Rotation3::from_axis_angle(y, ang).to_homogeneous() *
         geometry::Translation3::new(dx0, dy, 0.0).to_homogeneous();
     
-    let seed = vec![
+    let seed_orig = 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),
-        vertex( 0.5,  0.0, -0.5),        
+        vertex(-0.5,  0.0,  0.5),
         // TODO: Likewise factor these out
     ].iter().map(|v| incr * v).collect();
+    let seed = util::subdivide_cycle(&seed_orig, 2);
+    let n = seed.len();
+    // TODO: Factor out subdiv size
     
     RuleStep {
         geom: OpenMesh {
             verts: seed,
-            faces: vec![
-                Tag::Body(1), Tag::Parent(0), Tag::Body(0),
-                Tag::Parent(1), Tag::Parent(0), Tag::Body(1),
-                Tag::Body(2), Tag::Parent(1), Tag::Body(1),
-                Tag::Parent(2), Tag::Parent(1), Tag::Body(2),
-                Tag::Body(3), Tag::Parent(2), Tag::Body(2),
-                Tag::Parent(3), Tag::Parent(2), Tag::Body(3),
-                Tag::Body(0), Tag::Parent(3), Tag::Body(3),
-                Tag::Parent(0), Tag::Parent(3), Tag::Body(0),
-            ],
+            faces: util::parallel_zigzag_faces(n),
         },
         final_geom: prim::empty_mesh(), // TODO: Close properly
         children: vec![
             Child {
                 rule: Rule::Recurse(twist),
                 xf: incr,
-                vmap: vec![0,1,2,3],
+                vmap: (0..n).collect(),
             },
         ],
     }
@@ -366,6 +359,18 @@ pub fn twist() -> RuleStep {
 
 pub fn main() {
 
+    {
+        let vs = 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),
+        ];
+        let vs2 = util::subdivide_cycle(&vs, 2);
+        println!("vs={:?}", vs);
+        println!("vs2={:?}", vs2);
+    }
+    
     let run_test = |r: Rule, iters, name| {
         println!("Running {}...", name);
         let (mesh, nodes) = r.to_mesh(iters);

src/lib.rs

@@ -2,6 +2,7 @@ pub mod examples;
 pub mod openmesh;
 pub mod rule;
 pub mod prim;
+pub mod util;
 
 //pub use crate::examples;
 //pub use crate::openmesh::test_thing;

src/util.rs

@@ -0,0 +1,31 @@
+use crate::openmesh::{OpenMesh, Tag, Mat4, Vertex, vertex};
+use crate::rule::{Rule, RuleStep, Child};
+
+/// Linearly subdivides a list of points that are to be treated as a
+/// cycle.  This produces 'count' points for every element of 'p'
+/// (thus, the returned length will be `count*p.len()`).
+pub fn subdivide_cycle(p: &Vec<Vertex>, count: usize) -> Vec<Vertex> {
+    let n = p.len();
+    (0..n).map(|i| {
+        // The inner loop is interpolating between v1 and v2:
+        let v1 = &p[i];
+        let v2 = &p[(i+1) % n];
+        (0..count).map(move |j| {
+            // This is just lerping in count+1 equally spaced steps:
+            let f = (j as f32) / (count as f32);
+            v1*(1.0-f) + v2*f
+        })
+    }).flatten().collect()
+}
+// TODO: This can be generalized to an iterator or to IntoIterator
+// trait bound
+
+pub fn parallel_zigzag_faces(count: usize) -> Vec<Tag> {
+    (0..count).map(|i0| {
+        let i1 = (i0+1) % count;
+        vec![
+            Tag::Body(i1),   Tag::Parent(i0), Tag::Body(i0),
+            Tag::Parent(i1), Tag::Parent(i0), Tag::Body(i1),
+        ]
+    }).flatten().collect()
+}