From f41db779fcea0ae8493bd3f42c081dc311222346 Mon Sep 17 00:00:00 2001
From: Stewart Allen <stewart.allen@gmail.com>
Date: Sun, 26 Sep 2021 20:11:24 -0400
Subject: [PATCH] allow trace/follow + down to observe zThru when it is on the
 part bottom

---
 src/mode/cam/ops.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/mode/cam/ops.js b/src/mode/cam/ops.js
index 640a333e..4afc41c7 100644
--- a/src/mode/cam/ops.js
+++ b/src/mode/cam/ops.js
@@ -719,7 +719,7 @@
         slice(progress) {
             let { op, state } = this;
             let { tool, rate, down, plunge, offset } = op;
-            let { settings, widget, sliceAll, zMax, zTop, tabs } = state;
+            let { settings, widget, sliceAll, zMax, zTop, zThru, tabs } = state;
             let { updateToolDiams, cutTabs, cutPolys, healPolys } = state;
             let { process, stock } = settings;
             let poly2polyEmit = BASE.util.poly2polyEmit;
@@ -867,7 +867,11 @@
                         }
                         for (let pi of poly)
                         if (down) {
-                            for (let z of BASE.util.lerp(zTop, pi.getZ(), down)) {
+                            let zto = pi.getZ();
+                            if (zThru && similar(zto,0)) {
+                                zto -= zThru;
+                            }
+                            for (let z of BASE.util.lerp(zTop, zto, down)) {
                                 followZ(pi.clone().setZ(z));
                             }
                         } else {