smooth gyroid poly lines

web/kiri/gyroid-test.html

@@ -192,9 +192,42 @@
                 } while (added);
             } while (cleared < sparse.length);
 
+            // simplify poly
+            polys = polys.map(poly => filter(poly));
+
             return zcache[zkey] = {edge, points, dir, polys};
         }
 
+        function filter(poly) {
+            if (poly.length === 1) {
+                return poly;
+            }
+            let nuchain = [];
+            let e1 = poly[0];
+            let e2 = null;
+            let last = poly.length - 1;
+            for (let i=1; i<poly.length; i++) {
+                let el = poly[i];
+                if (e1.x === el.x || e1.y === el.y) {
+                    e2 = el;
+                    if (i < last) {
+                        continue;
+                    }
+                }
+                if (e2) {
+                    nuchain.push({x:(e1.x + e2.x)/2, y:(e1.y + e2.y)/2});
+                    e2 = null;
+                } else {
+                    nuchain.push(e1);
+                    if (i === last) {
+                        nuchain.push(el);
+                    }
+                }
+                e1 = el;
+            }
+            return nuchain;
+        }
+
         function dist(a, b, dir) {
             let dx = a.x - b.x;
             let dy = a.y - b.y;