diff --git a/package.json b/package.json
index c04c2fdf..8b49090c 100644
--- a/package.json
+++ b/package.json
@@ -29,7 +29,7 @@
         "connect": "^3.7.0",
         "earcut": "^2.2.3",
         "express-useragent": "^1.0.13",
-        "@jscad/modeling": "^2.9.2",
+        "@jscad/modeling": "^2.9.5",
         "jszip": "^3.7.1",
         "moment": "^2.24.0",
         "pixi.js": "^4.8.9",
diff --git a/src/add/array.js b/src/add/array.js
index a2449742..8530bd99 100644
--- a/src/add/array.js
+++ b/src/add/array.js
@@ -35,6 +35,12 @@ AP.peek = function() {
     return this[this.length - 1];
 };
 
+AP.drop = function(pre = 0, post = 0) {
+    while (pre-- > 0) this.shift();
+    while (post-- > 0) this.pop();
+    return this;
+};
+
 /**
  * allow chaining of push() calls
  */
diff --git a/src/geo/polygon.js b/src/geo/polygon.js
index 11ba8b3c..f4286781 100644
--- a/src/geo/polygon.js
+++ b/src/geo/polygon.js
@@ -1597,18 +1597,17 @@ class Polygon {
      * @param {Polygon} poly clipping mask
      * @returns {?Polygon[]}
      */
-    mask(poly, nullOnEquiv) {
+    mask(poly, nullOnEquiv, minarea) {
         let fillang = this.fillang && this.area() > poly.area() ? this.fillang : poly.fillang,
             clip = new clib.Clipper(),
             ctre = new clib.PolyTree(),
             sp1 = this.toClipper(),
             sp2 = poly.toClipper();
-
         clip.AddPaths(sp1, ptyp.ptSubject, true);
         clip.AddPaths(sp2, ptyp.ptClip, true);
 
         if (clip.Execute(ctyp.ctIntersection, ctre, cfil.pftEvenOdd, cfil.pftEvenOdd)) {
-            poly = POLY.fromClipperTree(ctre, poly.getZ());
+            poly = POLY.fromClipperTree(ctre, this.getZ(), undefined, undefined, minarea);
             poly.forEach(p => {
                 p.fillang = fillang;
             })
@@ -1779,6 +1778,29 @@ class Polygon {
 
         return null;
     }
+
+    annotate(obj = {}) {
+        Object.assign(this, obj);
+        return this;
+    }
+
+    extrude(z = 1) {
+        let poly = this.clone().setClockwise();
+        let faces = [];
+        let points = poly.points;
+        let length = points.length;
+        for (let i=0; i<length; i++) {
+            let p0 = points[i];
+            let p1 = points[(i + 1) % length];
+            faces.push(p0.x, p0.y, p0.z);
+            faces.push(p1.x, p1.y, p0.z);
+            faces.push(p1.x, p1.y, p1.z + z);
+            faces.push(p0.x, p0.y, p0.z);
+            faces.push(p1.x, p1.y, p1.z + z);
+            faces.push(p0.x, p0.y, p0.z + z);
+        }
+        return faces;
+    }
 }
 
 // use Slope.angleDiff() then re-test path mitering / rendering
diff --git a/src/geo/polygons.js b/src/geo/polygons.js
index 15195960..1b064920 100644
--- a/src/geo/polygons.js
+++ b/src/geo/polygons.js
@@ -7,7 +7,7 @@
 // use: ext.clip2
 // use: geo.slope
 // use: geo.polygon
-gapp.register("base.polygons", [], (root, exports) => {
+gapp.register("geo.polygons", [], (root, exports) => {
 
 const { base } = root;
 const { util, config, newPoint } = base;
@@ -388,7 +388,7 @@ function subtract(setA, setB, outA, outB, z, minArea, opt = {}) {
          }
      }
 
-     let out = polys.slice(), i, j, union, uset = [];
+     let out = polys.slice(), i, j, union, uset = [], a, b;
 
      outer: for (i=0; i<out.length; i++) {
          if (!out[i]) continue;
@@ -396,6 +396,10 @@ function subtract(setA, setB, outA, outB, z, minArea, opt = {}) {
              if (!out[j]) continue;
              union = out[i].union(out[j], minarea, all);
              if (union && union.length) {
+                 if (opt.onmerge) {
+                     a = out[i];
+                     b = out[j];
+                 }
                  out[i] = null;
                  out[j] = null;
                  if (all) {
@@ -403,6 +407,9 @@ function subtract(setA, setB, outA, outB, z, minArea, opt = {}) {
                  } else {
                      out.push(union);
                  }
+                 if (opt.onmerge) {
+                     opt.onmerge(a, b, union);
+                 }
                  continue outer;
              }
          }
diff --git a/src/kiri-mode/fdm/slice.js b/src/kiri-mode/fdm/slice.js
index c325edb9..e509bdbb 100644
--- a/src/kiri-mode/fdm/slice.js
+++ b/src/kiri-mode/fdm/slice.js
@@ -283,6 +283,7 @@ FDM.slice = function(settings, widget, onupdate, ondone) {
             for (let i=0; i<zi.length; i++) {
                 zi[i] = (zi[i] - zh[i] / 2).round(3);
             }
+            console.log({zi});
             return zi;
         },
         // slicer function (worker local or minion distributed)
@@ -818,7 +819,7 @@ function doRender(slice, isSynth, params, devel) {
     });
 
     if (slice.xray) {
-        const color = [ 0xff0000, 0x00aa00, 0x0000ff, 0xaaaa00, 0xff00ff ];
+        const color = [ 0xff0000, 0x00aa00, 0x0000ff, 0xaaaa00, 0xff00ff, 0x0 ];
         if (slice.lines) {
             slice.lines.forEach((line, i) => {
                 const group = i % 5;
diff --git a/src/kiri/api.js b/src/kiri/api.js
index 90f60d13..fbb4881d 100644
--- a/src/kiri/api.js
+++ b/src/kiri/api.js
@@ -47,8 +47,9 @@ const devel = {
     xray: (layers, raw) => {
         let proc = api.conf.get().process;
         let size = proc.sliceHeight || proc.slaSlice || 1;
+        let base = (proc.firstSliceHeight || size);
         layers = Array.isArray(layers) ? layers : [ layers ];
-        proc.xray = layers.map(l => raw ? l : l * size + size / 2);
+        proc.xray = layers.map(l => raw ? l : base + l * size - size / 2);
         api.function.slice();
     }
 };
diff --git a/src/load/obj.js b/src/load/obj.js
index 58138b6a..cc3cfd30 100644
--- a/src/load/obj.js
+++ b/src/load/obj.js
@@ -59,7 +59,6 @@ function parse(text) {
                 break;
         }
     }
-
     return objs;
 }
 
diff --git a/src/main/mesh.js b/src/main/mesh.js
index 30a0f375..67eee197 100644
--- a/src/main/mesh.js
+++ b/src/main/mesh.js
@@ -12,6 +12,7 @@
 // dep: mesh.model
 // dep: mesh.build
 // dep: load.file
+// use: geo.polygons
 gapp.main("main.mesh", [], (root) => {
 
 const { Quaternion, Mesh, MeshPhongMaterial, PlaneGeometry, DoubleSide, Vector3 } = THREE;
diff --git a/web/mesh/index.css b/web/mesh/index.css
index 875ef009..00c0cfab 100644
--- a/web/mesh/index.css
+++ b/web/mesh/index.css
@@ -432,6 +432,7 @@ button.selected:hover {
 
 #modes {
     position: absolute;
+    gap: 2px;
     top: 0;
     left: 50%;
     transform: translateX(-50%);