add CAM Z bottom visualization, make it relative to stock instead of part

src/kiri-mode/cam/slice.js

@@ -34,12 +34,13 @@ CAM.slice = function(settings, widget, onupdate, ondone) {
         camOps = widget.camops = [],
         sliceAll = widget.slices = [],
         bounds = widget.getBoundingBox(),
-        zBottom = proc.camZBottom,
+        wztop = widget.track.top,
+        ztOff = hasStock ? stock.z - wztop : 0,
+        zbOff = hasStock ? wztop - widget.track.box.d : 0,
+        zBottom = proc.camZBottom - zbOff,
         zMin = Math.max(bounds.min.z, zBottom),
         zMax = bounds.max.z,
         zThru = zBottom === 0 ? (proc.camZThru || 0) : 0,
-        wztop = widget.track.top,
-        ztOff = hasStock ? stock.z - wztop : 0,
         zTop = zMax + ztOff,
         minToolDiam = Infinity,
         maxToolDiam = -Infinity,