in cam animation, add red tinting to cuts below z=0

src/mesh/api.js

@@ -1097,9 +1097,11 @@ const tool = {
         if (dup_sel) {
             selection.clear();
         }
+        let nm = [];
         for (let m of models) {
-            m.duplicate({ select: dup_sel, shift: dup_shift });
+            nm.push(m.duplicate({ select: dup_sel, shift: dup_shift }));
         }
+        tool.regroup(nm);
     },
 
     mirror() {

src/mesh/model.js

@@ -80,7 +80,7 @@ let materials = mesh.material = {
         color: 0x0,
         transparent: true,
         opacity: 0.5
-    })
+    }),
 };
 
 /** 3D model rendered on plaform **/