Added source code

utils/offset.scad

@@ -0,0 +1,63 @@
+//
+// NopSCADlib Copyright Chris Palmer 2018
+// nop.head@gmail.com
+// hydraraptor.blogspot.com
+//
+// This file is part of NopSCADlib.
+//
+// NopSCADlib is free software: you can redistribute it and/or modify it under the terms of the
+// GNU General Public License as published by the Free Software Foundation, either version 3 of
+// the License, or (at your option) any later version.
+//
+// NopSCADlib is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+// without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with NopSCADlib.
+// If not, see <https://www.gnu.org/licenses/>.
+//
+
+//! 3D offset using `minkowski` with a `sphere`, so very slow if `$fn` is not kept small. The offset can be positive or negative.
+//!
+//! Can be used to round corners. Positive offsets will round convex corners, negative offsets round concave corners. To round both use [`round_3D()`](#round).
+//!
+//! If `chamfer_base` is true then the bottom edge is made suitable for 3D printing by chamfering when the angle gets shallower than 45 degrees.
+include <../core.scad>
+
+module offset_3D(r, chamfer_base = false) { //! Offset 3D shape by specified radius ```r```, positive or negative.
+    module ball(r)
+        if(chamfer_base)
+            rotate_extrude()
+                intersection() {
+                    rotate(180)
+                        teardrop(0, r);
+
+                    translate([0, -r])
+                        square([r, 2 * r]);
+                }
+        else
+            sphere(r);
+
+    if(r > 0)
+        minkowski() {
+            children();
+
+            ball(r);
+        }
+    else
+        if(r < 0)
+            render() difference() {
+                cube(inf / 2, center = true);
+
+                minkowski() {
+                    difference() {
+                        cube(inf, center = true);
+
+                        children();
+                    }
+                    ball(-r);
+                }
+            }
+        else
+            children();
+}