fix slice first height with grouped parts

js/kiri-driver-fdm.js

@@ -107,7 +107,17 @@ let gs_kiri_fdm = exports;
         }
 
         function onSliceDone(slices) {
-            slices = slices.filter(slice => slice.tops.length);
+            // slices = slices.filter(slice => slice.tops.length);
+            // remove all empty slices above part but leave below
+            // for multi-part (multi-extruder) setups where the void is ok
+            let found = false;
+            slices = slices.reverse().filter(slice => {
+                if (slice.tops.length) {
+                    return found = true;
+                } else {
+                    return found;
+                }
+            }).reverse();
 
             widget.slices = slices;
 

js/kiri-slicer.js

@@ -103,7 +103,7 @@ let gs_kiri_slicer = exports;
             bounds = btmp;
         }
 
-        let zMin = options.zmin || Math.floor(bounds.min.z),
+        let zMin = options.zmin || options.firstHeight || Math.floor(bounds.min.z),
             zMax = options.zmax || Math.ceil(bounds.max.z),
             zInc = options.height,
             zIncMin = options.minHeight,