added hull_polyline2d

README.md

@@ -28,6 +28,7 @@ Some modules may depend on other modules. For example, the `polyline2d` module d
 	- [rounded_square](https://openhome.cc/eGossip/OpenSCAD/lib-rounded_square.html)
 	- [line2d](https://openhome.cc/eGossip/OpenSCAD/lib-line2d.html)
 	- [polyline2d](https://openhome.cc/eGossip/OpenSCAD/lib-polyline2d.html)
+	- [hull_polyline2d](https://openhome.cc/eGossip/OpenSCAD/lib-hull_polyline2d.html)
 	- [circular_sector](https://openhome.cc/eGossip/OpenSCAD/lib-circular_sector.html)
 	- [arc](https://openhome.cc/eGossip/OpenSCAD/lib-arc.html)
 	- [hexagons](https://openhome.cc/eGossip/OpenSCAD/lib-hexagons.html)

docs/lib-hull_polyline2d.md

@@ -0,0 +1,22 @@
+# hull_polyline2d
+
+Creates a 2D polyline from a list of `[x, y]` coordinates. As the name says, it uses the built-in hull operation for each pair of points (created by the `circle` module). It's slow. However, it can be used to create metallic effects for a small `$fn`, large `$fa` or `$fs`.
+
+## Parameters
+
+- `points` : The list of `[x, y]` points of the polyline. The points are indexed from 0 to n-1.
+- `width` : The line width.
+- `$fa`, `$fs`, `$fn` : Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
+
+## Examples
+
+	include <hull_polyline2d.scad>;
+	
+	$fn = 4;
+	
+	hull_polyline2d(
+	    points = [[1, 2], [-5, -4], [-5, 3], [5, 5]], 
+	    width = 1
+	);
+
+![hull_polyline3d](images/lib-hull_polyline2d-1.JPG)

src/hull_polyline2d.scad

@@ -0,0 +1,36 @@
+/**
+* hull_polyline2d.scad
+*
+* Creates a 2D polyline from a list of `[x, y]` coordinates. 
+* As the name says, it uses the built-in hull operation for each pair of points (created by the circle module). 
+* It's slow. However, it can be used to create metallic effects for a small $fn, large $fa or $fs.
+* 
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/hull_polyline2d.html
+*
+**/
+
+module hull_polyline2d(points, width) {
+    half_width = width / 2;
+    leng = len(points);
+    
+    module hull_line2d(index) {
+        hull() {
+            translate(points[index - 1]) 
+                circle(half_width);
+            translate(points[index]) 
+                circle(half_width);
+        }
+    }
+
+    module polyline2d_inner(index) {
+        if(index < leng) {
+            hull_line2d(index);
+            polyline2d_inner(index + 1);
+        }
+    }
+
+    polyline2d_inner(1);
+}