add

README.md

@@ -88,6 +88,7 @@ Too many dependencies? Because OpenSCAD doesn't provide namespace management, I
 	- [shape_trapezium](https://openhome.cc/eGossip/OpenSCAD/lib-shape_trapezium.html)
 	- [shape_cyclicpolygon](https://openhome.cc/eGossip/OpenSCAD/lib-shape_cyclicpolygon.html)
     - [shape_pentagram](https://openhome.cc/eGossip/OpenSCAD/lib-shape_pentagram.html)	
+    - [shape_starburst](https://openhome.cc/eGossip/OpenSCAD/lib-shape_starburst.html)	    
 	- [shape_superformula](https://openhome.cc/eGossip/OpenSCAD/lib-shape_superformula.html)
 	- [shape_glued2circles](https://openhome.cc/eGossip/OpenSCAD/lib-shape_glued2circles.html)
 	- [shape_path_extend](https://openhome.cc/eGossip/OpenSCAD/lib-shape_path_extend.html)		

docs/lib-shape_starburst.md

@@ -0,0 +1,39 @@
+# shape_starburst
+
+Returns shape points of a star. They can be used with xxx_extrude modules of dotSCAD. The shape points can be also used with the built-in polygon module. 
+
+## Parameters
+
+- `r1` : The outer radius of the starburst. 
+- `r2` : The inner radius of the starburst.
+- `n`  : The number of vertices. 
+
+
+## Examples
+
+	include <shape_starburst.scad>;
+	
+	polygon(shape_starburst(30, 12, 6));
+
+![shape_starburst](images/lib-shape_starburst-1.JPG)
+
+	include <shape_starburst.scad>;
+	include <circle_path.scad>;
+	include <rotate_p.scad>;
+	include <golden_spiral.scad>;
+	include <cross_sections.scad>;
+	include <polysections.scad>;
+	include <golden_spiral_extrude.scad>;
+	
+	shape_pts = shape_starburst(5, 2, 8);
+	
+	golden_spiral_extrude(
+	    shape_pts, 
+	    from = 5, 
+	    to = 10, 
+	    point_distance = 1,
+	    scale = 10
+	);
+
+![shape_pentagram](images/lib-shape_starburst-2.JPG)
+

src/shape_starburst.scad

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+/**
+* shape_star.scad
+*
+* Returns shape points of a starburst.
+* They can be used with xxx_extrude modules of dotSCAD.
+* The shape points can be also used with the built-in polygon module. 
+*
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-shape_starburst.html
+*
+**/
+
+function __outer_points(r1, r2, n) = 
+    let(
+        a = 360 / n
+    )
+    [for(i = [0:n-1]) [r1 * cos(a * i), r1 * sin(a * i)]];
+function __inner_points(r1, r2, n) = 
+    let (
+        a = 360 / n,
+        half_a = a / 2
+    )
+    [for(i = [0:n-1]) [r2 * cos(a * i + half_a), r2 * sin(a * i + half_a)]];
+    
+function __one_by_one(outer_points, inner_points, i = 0) =
+        len(outer_points) == i ? [] :
+        concat([outer_points[i], inner_points[i]], __one_by_one(outer_points, inner_points, i + 1));    
+
+function shape_starburst(r1, r2, n) = __one_by_one(__outer_points(r1, r2, n), __inner_points(r1, r2, n));