diff --git a/release.md b/release.md
index 5f04d58d..ffaac0fc 100644
--- a/release.md
+++ b/release.md
@@ -5,6 +5,7 @@ Full docs @ https://docs.grid.space/projects/kiri-moto
 
 # Release 3.6
 
+* improved FDM preview rendering speed and reduced memory usage
 * threaded task and message passing performance improvements
 * refactor FDM supports and synthetic widgets to use more common code
 * allow FDM mixing of automatic and manual / detected supports
diff --git a/src/kiri/codec.js b/src/kiri/codec.js
index c476f8fa..c2a2ae75 100644
--- a/src/kiri/codec.js
+++ b/src/kiri/codec.js
@@ -365,6 +365,16 @@ registerDecoder(TYPE.POLY, function(v, state) {
 
 // ----- Layers Codec -----
 
+function encodeLayerPolys(polys, state) {
+    return polys.map(poly => {
+        return {
+            open: poly.open,
+            color: poly.color,
+            points: codec.encodePointArray(poly.points, state.zeros)
+        }
+    });
+}
+
 kiri.Layers.prototype.encode = function(state) {
     let zeros = state.zeros;
     let enc = {
@@ -377,7 +387,7 @@ kiri.Layers.prototype.encode = function(state) {
                 off: layer.off,
                 color: layer.color,
                 // 1D lines and polylines
-                polys: encode(layer.polys, state),
+                polys: encodeLayerPolys(layer.polys, state),
                 lines: encodePointArray(layer.lines, state),
                 // 2D lines and flat areas
                 faces: codec.allocFloat32Array(layer.faces, zeros),
@@ -409,8 +419,8 @@ registerDecoder(TYPE.LAYERS, function(v, state) {
         const d = render.layers[layers[i]] = {
             off: data.off,
             color: data.color,
-            polys: decode(data.polys, state),
-            lines: decodePointArray(data.lines),
+            polys: data.polys,
+            lines: data.lines,
             faces: codec.allocFloat32Array(data.faces),
             norms: codec.allocFloat32Array(data.norms),
             cface: data.cface,
diff --git a/src/kiri/stack.js b/src/kiri/stack.js
index 9fdf9c45..51bf3955 100644
--- a/src/kiri/stack.js
+++ b/src/kiri/stack.js
@@ -89,15 +89,13 @@ class Stack {
     renderLayer(layer, group) {
         function addPoly(vertices, poly) {
             const points = poly.points, len = points.length;
-            for (let i=1; i<len; i++) {
-                const p1 = points[i-1], p2 = points[i];
-                vertices.push(new THREE.Vector3(p1.x, p1.y, p1.z));
-                vertices.push(new THREE.Vector3(p2.x, p2.y, p2.z));
+            for (let i=3; i<len; i += 3) {
+                vertices.push(new THREE.Vector3(points[i-3], points[i-2], points[i-1]));
+                vertices.push(new THREE.Vector3(points[i+0], points[i+1], points[i+2]));
             }
             if (!poly.open) {
-                const p1 = points[len - 1], p2 = points[0];
-                vertices.push(new THREE.Vector3(p1.x, p1.y, p1.z));
-                vertices.push(new THREE.Vector3(p2.x, p2.y, p2.z));
+                vertices.push(new THREE.Vector3(points[len-3], points[len-2], points[len-1]));
+                vertices.push(new THREE.Vector3(points[0], points[1], points[2]));
             }
         }
 
@@ -134,9 +132,8 @@ class Stack {
                 }
             }
             // for now, line segments inherit the last color
-            for (let i=0, il=lines.length; i<il; i++) {
-                const p = lines[i];
-                vert.push(new THREE.Vector3(p.x, p.y, p.z));
+            for (let i=0, il=lines.length; i<il; i += 3) {
+                vert.push(new THREE.Vector3(lines[i], lines[i+1], lines[i+1]));
             }
             // ensure at least one group using the default color settings
             if (grp.length === 0) {