diff --git a/src/main.ts b/src/main.ts
index 509f07e..ebaed73 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -3,7 +3,7 @@ import { vec2, type Vec2 } from "@thi.ng/vectors"
 import { $canvas } from "@thi.ng/rdom-canvas";
 import { reactive, sync } from "@thi.ng/rstream";
 import { $compile, $input, $inputNum } from '@thi.ng/rdom'
-import { cycle, comp, range, iterator, map, mapcat, reverse, zip } from "@thi.ng/transducers"
+import { cycle, comp, range, iterator, map, mapcat, reverse, zip, filter } from "@thi.ng/transducers"
 
 // initial settings
 
@@ -50,10 +50,10 @@ const secondaryColor = getComputedStyle(document.documentElement).getPropertyVal
 
 const stitches = (seed: number, maxCoord: number) =>
   iterator(
-    mapcat((cell) => (cell + seed) % 2 === 0 // start at the beginning or skip it
-      ? [vec2(cell, cell + 1)]
-      : null)
-    ,
+    comp(
+      filter((cell) => (cell + seed) % 2 === 0), // start at the beginning or skip it
+      map((cell) => vec2(cell, cell + 1))
+    ),
     range(maxCoord)
   )
 
@@ -62,18 +62,19 @@ const yLineGen = (coord: number, [p1, p2]: Vec2) => line([coord, p1], [coord, p2
 
 const generateLines = (maxCoordOnAxis: number, maxCoordPerpendicular: number, seeds: Iterable<number>, lineGen: (coord: number, l: Vec2) => Line) =>
   iterator(
-    mapcat(([coord, seed]) => {
+    comp(
+      map(([coord, seed]) => [coord, stitches(seed, maxCoordPerpendicular)] as const),
       // optimization for quicker drawing: when we're in an odd row / col,
       // reverse drawing direction
-      const onEvenCoord = coord % 2 === 0
-      return iterator(
-        comp(
-          map(l => lineGen(coord, l)),
-          map(l => onEvenCoord ? l : flip(l))
-        ),
-        onEvenCoord ? stitches(seed, maxCoordPerpendicular) : reverse(stitches(seed, maxCoordPerpendicular))
+      mapcat(([coord, stitches]) =>
+        map(
+          l => lineGen(coord, l),
+          coord % 2 === 0
+            ? stitches
+            : reverse(map(([p1, p2]) => vec2(p2, p1), stitches))
+        )
       )
-    }),
+    ),
     zip(range(maxCoordOnAxis + 1), seeds)
   )