diff --git a/src/kiri/export.js b/src/kiri/export.js
index 03b67adf..0585a199 100644
--- a/src/kiri/export.js
+++ b/src/kiri/export.js
@@ -19,24 +19,14 @@
 
     let printSeq = parseInt(SDB['kiri-print-seq'] || SDB['print-seq'] || "0") + 1;
 
-    function isPrepared() {
-        return API.view.get() === API.const.VIEWS.PREVIEW;
-    }
-
     function exportFile(options) {
-        if (isPrepared()) {
-            const mode = API.mode.get();
-            API.event.emit('export', mode);
-            switch (mode) {
-                case 'LASER': return callExportLaser(options);
-                case 'FDM': return callExport(options, mode);
-                case 'CAM': return callExport(options, mode);
-                case 'SLA': return callExportSLA(options);
-            }
-        } else {
-            API.function.prepare(function() {
-                exportFile(options)
-            });
+        const mode = API.mode.get();
+        API.event.emit('export', mode);
+        switch (mode) {
+            case 'LASER': return callExportLaser(options);
+            case 'FDM': return callExport(options, mode);
+            case 'CAM': return callExport(options, mode);
+            case 'SLA': return callExportSLA(options);
         }
     }
 
diff --git a/src/kiri/init.js b/src/kiri/init.js
index 833c79ef..db29e41b 100644
--- a/src/kiri/init.js
+++ b/src/kiri/init.js
@@ -154,7 +154,10 @@
         UI.fps.style.display = on ? 'block' : '';
         if (on) {
             setInterval(() => {
-                UI.fps.innerText = SPACE.view.getFPS().toFixed(2);
+                const nv = SPACE.view.getFPS().toFixed(2);
+                if (nv !== UI.fps.innerText) {
+                    UI.fps.innerText = nv;
+                }
             }, 100);
         }
     }
diff --git a/src/kiri/main.js b/src/kiri/main.js
index 9d02379b..d3904983 100644
--- a/src/kiri/main.js
+++ b/src/kiri/main.js
@@ -42,6 +42,7 @@
         MODE = MODES.FDM,
         STACKS = KIRI.stacks,
         DRIVER = undefined,
+        complete = {},
         onEvent = {},
         selectedMeshes = [],
         localFilterKey ='kiri-gcode-filters',
@@ -239,7 +240,7 @@
             slice: prepareSlices,
             print: preparePreview,
             prepare: preparePreview,
-            export: function() { KIRI.export(...arguments) },
+            export: prepareExport,
             cancel: cancelWorker,
             clear: KIRI.client.clear
         },
@@ -696,6 +697,9 @@
             callback = preparePreview;
         }
 
+        // clear completion marks
+        complete = {};
+
         hideSlider(true);
         platform.deselect();
         setViewMode(VIEWS.SLICE);
@@ -752,6 +756,8 @@
                     API.event.emit('slice.end', getMode());
                     // print stats
                     DBUG.log(segtimes);
+                    // mark slicing complete for prep/preview
+                    complete.slice = true;
                     if (callback && typeof callback === 'function') {
                         callback();
                     }
@@ -783,11 +789,14 @@
     }
 
     function preparePreview(callback) {
-        if (viewMode === VIEWS.PREVIEW) return;
-        if (viewMode === VIEWS.ARRANGE) {
+        if (complete.preview) {
+            return;
+        }
+        if (!complete.slice) {
             prepareSlices(() => {
                 preparePreview(callback);
             });
+            return;
         }
 
         hideSlider(true);
@@ -834,12 +843,27 @@
                 updateSpeeds(maxSpeed);
             }
 
+            // mark preview complete for export
+            complete.preview = true;
+
             if (typeof(callback) === 'function') {
                 callback();
             }
         });
     }
 
+    function prepareExport() {
+        const argsave = arguments;
+        if (!complete.preview) {
+            preparePreview(() => {
+                prepareExport(...argsave);
+            });
+            return;
+        }
+        complete.export = true;
+        KIRI.export(...argsave);
+    }
+
     function loadCode(code, type) {
         setViewMode(VIEWS.PREVIEW);
         setOpacity(0);
diff --git a/src/mode/cam/topo.js b/src/mode/cam/topo.js
index de4b7ee6..9b848568 100644
--- a/src/mode/cam/topo.js
+++ b/src/mode/cam/topo.js
@@ -133,6 +133,7 @@
 
             function push_point(x,y,z) {
                 const newP = newPoint(x,y,z);
+                // todo: merge co-linear, not just co-planar
                 if (lastP && lastP.z === z) {
                     if (curvesOnly) {
                         end_poly();
@@ -189,7 +190,6 @@
                         // eliminate if points "under" other lines
                         for (let j=0; j<len; j++) {
                             // skip self and adjacent
-                            // if (j === i) continue;
                             if (j >= i-1 && j <= i+1) continue;
                             let l2 = lines[j], p3 = l2.p1, p4 = l2.p2;
                             // sort p3,p4 by y for comparison
@@ -211,7 +211,7 @@
                         .addPolys(slice.topPolys());
                 });
 
-                // for each Y slice, find z grid value (x/z swapped)
+                // raster grid: for each Y slice, find z grid value (x/z swapped)
                 for (j=0, jl=slices.length; j<jl; j++) {
                     const slice = slices[j];
                     const points = slice.points;