Added helper function to avoid juggling of indices

README.md

@@ -3,8 +3,7 @@
 ## Highest priority:
 
 - If my `closure_try2` branch seems to be working: start converting
-  other things and cleaning them up.  Modify `twist` to have the
-  things I wrote this for in the first place!
+  other things and cleaning everything up.  (`twist` is still ugly.)
 - See `automata_scratch/examples.py` and implement some of the tougher
   examples.
   - `spiral_nested_2` & `spiral_nested_3` (how to compose
@@ -21,10 +20,12 @@
   - What patterns can I factor out?  I do some things regularly, like:
     the clockwise boundaries, the zigzag connections, the iterating over
     a `Vec<Vertex>` to transform each element and make another vector.
-  - I have seen many of my bugs come from: all this arithmetic on
-    indices.  I generate vertex maps more or less manually.
 - Docs on modules
 - Grep for all TODOs in code, really.
+- Look at performance.  Can I save on copies of geometry by using
+  `Rc<OpenMesh>` or the like?  In many cases I have nothing but copied
+  geometry.  Can I pre-allocate vectors instead of
+  extending/appending?
 - Look at everything in README.md in automata_scratch.
 
 ## If I'm bored:

src/examples.rs

@@ -375,7 +375,6 @@ fn twist(f: f32, subdiv: usize) -> Rule {
         vertex( 0.5,  0.0,  0.5),
         vertex(-0.5,  0.0,  0.5),
     ], &xf);
-    //let seed_sub = util::subdivide_cycle(&seed, subdiv);
     let dx0: f32 = 1.5;
     let dy: f32 = 0.1/f;
     let ang: f32 = 0.05/f;
@@ -434,12 +433,12 @@ fn twist(f: f32, subdiv: usize) -> Rule {
     
     let start = move |self_: Rc<Rule>| -> RuleEval {
         
-        let xform = |dx, i, ang0| -> Mat4 {
-            (geometry::Rotation3::from_axis_angle(&y, ang0 + (qtr * (i as f32))).to_homogeneous() *
+        let xform = |dx, i, ang0, div| -> Mat4 {
+            (geometry::Rotation3::from_axis_angle(&y, ang0 + (qtr / div * (i as f32))).to_homogeneous() *
              geometry::Translation3::new(dx, 0.0, 0.0).to_homogeneous())
         };
 
-        let make_child = |i, dx, incr, ang0| -> (Child, OpenMesh) {
+        let make_child = |i, incr, xform| -> (OpenMesh, Child) {
             
             let seed_orig = transform(&seed, &incr);
             let seed_sub = util::subdivide_cycle(&seed_orig, subdiv);
@@ -447,32 +446,23 @@ fn twist(f: f32, subdiv: usize) -> Rule {
             
             let c = Child {
                 rule: Rc::new(Rule { eval: (recur.clone())(incr) }),
-                xf: xform(dx, i, ang0),
-                vmap: ((n+1)*i..(n+1)*(i+count)).collect(), // N.B.
-                // note n+1, not n. the +1 is for the centroid below
-                // TODO: The above vmap is wrong when I call
-                // 'make_child' twice and then append.
+                xf: xform,
+                vmap: (0..(n+1)).collect(),
+                // N.B. n+1, not n. the +1 is for the centroid below
             };
-            let mut vs = transform(&seed_sub, &c.xf);
+            let mut vs = transform(&seed_sub, &xform);
             // and in the process, generate faces for these seeds:
             let (centroid, f) = util::connect_convex(&vs, false);
             vs.push(centroid);
-            (c, OpenMesh { verts: vs, faces: f })
+            (OpenMesh { verts: vs, faces: f }, c)
         };
         
-        // First generate 'count' children, each one shifted/rotated
-        // differently:
-        let children_inner = (0..count).map(|i| make_child(i, dx0, incr_inner, 0.0));
-        let children_outer = (0..count).map(|i| make_child(i + count, dx0*2.0, incr_outer, qtr/2.0));
-        // TODO: the +count is only to work around vmap kludges
-        
-        let (children, meshes): (Vec<_>, Vec<_>) = children_inner.chain(children_outer).unzip();
+        // Generate 'count' children, shifted/rotated differently:
+        let children_inner = (0..count).map(|i| make_child(i, incr_inner, xform(dx0, i, 0.0, 1.0)));
+        let children_outer = (0..count).map(|i| make_child(i, incr_outer, xform(dx0*2.0, i, qtr/2.0, 2.0)));
 
-        RuleEval {
-            geom: OpenMesh::append(meshes),
-            final_geom: prim::empty_mesh(),
-            children: children,
-        }
+        RuleEval::from_pairs(
+            children_inner.chain(children_outer), prim::empty_mesh())
     };
     
     Rule { eval: Box::new(start) }

src/openmesh.rs

@@ -45,10 +45,16 @@ pub struct OpenMesh {
 
 impl OpenMesh {
 
-    pub fn append<T, U>(meshes: T) -> OpenMesh
+    /// Appends any number of meshes together.  Returns both a single
+    /// mesh, and a vector which gives the offset by which each
+    /// corresponding input mesh was shifted.  That is, for the i'th
+    /// index in `meshes`, all of its triangle indices were shifted by
+    /// the i'th offset in the resultant mesh.
+    pub fn append<T, U>(meshes: T) -> (OpenMesh, Vec<usize>)
     where U: Borrow<OpenMesh>,
           T: IntoIterator<Item = U>
     {
+        let mut offsets: Vec<usize> = vec![];
         let mut v: Vec<Vertex> = vec![];
         let mut f: Vec<Tag> = vec![];
         for mesh_ in meshes {
@@ -57,6 +63,7 @@ impl OpenMesh {
             // Position in 'verts' at which we're appending
             // mesh.verts, which we need to know to shift indices:
             let offset = v.len();
+            offsets.push(offset);
             
             // Copy all vertices:
             v.append(&mut mesh.verts.clone());
@@ -70,7 +77,7 @@ impl OpenMesh {
             }));
         }
            
-        OpenMesh { verts: v, faces: f }
+        (OpenMesh { verts: v, faces: f }, offsets)
     }
     
     /// Returns a new `OpenMesh` whose vertices have been transformed.

src/rule.rs

@@ -1,5 +1,6 @@
 use crate::openmesh::{OpenMesh, Tag, Mat4};
 //use crate::prim;
+use std::borrow::Borrow;
 use std::rc::Rc;
 
 pub type RuleFn = Box<dyn Fn(Rc<Rule>) -> RuleEval>;
@@ -254,3 +255,35 @@ impl Rule {
     }
     
 }
+
+impl RuleEval {
+    /// Turn an iterator of (OpenMesh, Child) into a single RuleEval.
+    /// All meshes are merged, and the `vmap` in each child has the
+    /// correct offsets applied to account for this merge.
+    ///
+    /// (`final_geom` is passed through to the RuleEval unmodified.)
+    pub fn from_pairs<T, U>(m: T, final_geom: OpenMesh) -> RuleEval
+        where U: Borrow<OpenMesh>,
+              T: IntoIterator<Item = (U, Child)>
+    {
+        let (meshes, children): (Vec<_>, Vec<_>) = m.into_iter().unzip();
+        let (mesh, offsets) = OpenMesh::append(meshes);
+
+        // Patch up vmap in each child, and copy everything else:
+        let children2: Vec<Child> = children.iter().zip(offsets.iter()).map(|(c,off)| {
+            Child {
+                rule: c.rule.clone(),
+                xf: c.xf.clone(),
+                // simply add offset:
+                vmap: c.vmap.iter().map(|i| i + off).collect(),
+            }
+        }).collect();
+
+        RuleEval {
+            geom: mesh,
+            final_geom: final_geom,
+            children: children2,
+        }
+    }
+
+}